Nodes


OpenShift Container Platform 4.12

Configuring and managing nodes in OpenShift Container Platform

Red Hat OpenShift Documentation Team

Abstract

This document provides instructions for configuring and managing the nodes, Pods, and containers in your cluster. It also provides information on configuring Pod scheduling and placement, using jobs and DaemonSets to automate tasks, and other tasks to ensure an efficient cluster.

Chapter 1. Overview of nodes

1.1. About nodes

A node is a virtual or bare-metal machine in a Kubernetes cluster. Worker nodes host your application containers, grouped as pods. The control plane nodes run services that are required to control the Kubernetes cluster. In OpenShift Container Platform, the control plane nodes contain more than just the Kubernetes services for managing the OpenShift Container Platform cluster.

Having stable and healthy nodes in a cluster is fundamental to the smooth functioning of your hosted application. In OpenShift Container Platform, you can access, manage, and monitor a node through the Node object representing the node. Using the OpenShift CLI (oc) or the web console, you can perform the following operations on a node.

The following components of a node are responsible for maintaining the running of pods and providing the Kubernetes runtime environment.

Container runtime
The container runtime is responsible for running containers. Kubernetes offers several runtimes such as containerd, cri-o, rktlet, and Docker.
Kubelet
Kubelet runs on nodes and reads the container manifests. It ensures that the defined containers have started and are running. The kubelet process maintains the state of work and the node server. Kubelet manages network rules and port forwarding. The kubelet manages containers that are created by Kubernetes only.
Kube-proxy
Kube-proxy runs on every node in the cluster and maintains the network traffic between the Kubernetes resources. A Kube-proxy ensures that the networking environment is isolated and accessible.
DNS
Cluster DNS is a DNS server which serves DNS records for Kubernetes services. Containers started by Kubernetes automatically include this DNS server in their DNS searches.
Overview of control plane and worker node
Read operations

The read operations allow an administrator or a developer to get information about nodes in an OpenShift Container Platform cluster.

Management operations

As an administrator, you can easily manage a node in an OpenShift Container Platform cluster through several tasks:

  • Add or update node labels. A label is a key-value pair applied to a Node object. You can control the scheduling of pods using labels.
  • Change node configuration using a custom resource definition (CRD), or the kubeletConfig object.
  • Configure nodes to allow or disallow the scheduling of pods. Healthy worker nodes with a Ready status allow pod placement by default while the control plane nodes do not; you can change this default behavior by configuring the worker nodes to be unschedulable and the control plane nodes to be schedulable.
  • Allocate resources for nodes using the system-reserved setting. You can allow OpenShift Container Platform to automatically determine the optimal system-reserved CPU and memory resources for your nodes, or you can manually determine and set the best resources for your nodes.
  • Configure the number of pods that can run on a node based on the number of processor cores on the node, a hard limit, or both.
  • Reboot a node gracefully using pod anti-affinity.
  • Delete a node from a cluster by scaling down the cluster using a compute machine set. To delete a node from a bare-metal cluster, you must first drain all pods on the node and then manually delete the node.
Enhancement operations

OpenShift Container Platform allows you to do more than just access and manage nodes; as an administrator, you can perform the following tasks on nodes to make the cluster more efficient, application-friendly, and to provide a better environment for your developers.

1.2. About pods

A pod is one or more containers deployed together on a node. As a cluster administrator, you can define a pod, assign it to run on a healthy node that is ready for scheduling, and manage. A pod runs as long as the containers are running. You cannot change a pod once it is defined and is running. Some operations you can perform when working with pods are:

Read operations

As an administrator, you can get information about pods in a project through the following tasks:

Management operations

The following list of tasks provides an overview of how an administrator can manage pods in an OpenShift Container Platform cluster.

Enhancement operations

You can work with pods more easily and efficiently with the help of various tools and features available in OpenShift Container Platform. The following operations involve using those tools and features to better manage pods.

OperationUserMore information

Create and use a horizontal pod autoscaler.

Developer

You can use a horizontal pod autoscaler to specify the minimum and the maximum number of pods you want to run, as well as the CPU utilization or memory utilization your pods should target. Using a horizontal pod autoscaler, you can automatically scale pods.

Install and use a vertical pod autoscaler.

Administrator and developer

As an administrator, use a vertical pod autoscaler to better use cluster resources by monitoring the resources and the resource requirements of workloads.

As a developer, use a vertical pod autoscaler to ensure your pods stay up during periods of high demand by scheduling pods to nodes that have enough resources for each pod.

Provide access to external resources using device plugins.

Administrator

A device plugin is a gRPC service running on nodes (external to the kubelet), which manages specific hardware resources. You can deploy a device plugin to provide a consistent and portable solution to consume hardware devices across clusters.

Provide sensitive data to pods using the Secret object.

Administrator

Some applications need sensitive information, such as passwords and usernames. You can use the Secret object to provide such information to an application pod.

1.3. About containers

A container is the basic unit of an OpenShift Container Platform application, which comprises the application code packaged along with its dependencies, libraries, and binaries. Containers provide consistency across environments and multiple deployment targets: physical servers, virtual machines (VMs), and private or public cloud.

Linux container technologies are lightweight mechanisms for isolating running processes and limiting access to only designated resources. As an administrator, You can perform various tasks on a Linux container, such as:

OpenShift Container Platform provides specialized containers called Init containers. Init containers run before application containers and can contain utilities or setup scripts not present in an application image. You can use an Init container to perform tasks before the rest of a pod is deployed.

Apart from performing specific tasks on nodes, pods, and containers, you can work with the overall OpenShift Container Platform cluster to keep the cluster efficient and the application pods highly available.

1.4. About autoscaling pods on a node

OpenShift Container Platform offers three tools that you can use to automatically scale the number of pods on your nodes and the resources allocated to pods.

Horizontal Pod Autoscaler

The Horizontal Pod Autoscaler (HPA) can automatically increase or decrease the scale of a replication controller or deployment configuration, based on metrics collected from the pods that belong to that replication controller or deployment configuration.

For more information, see Automatically scaling pods with the horizontal pod autoscaler.

Custom Metrics Autoscaler

The Custom Metrics Autoscaler can automatically increase or decrease the number of pods for a deployment, stateful set, custom resource, or job based on custom metrics that are not based only on CPU or memory.

For more information, see Custom Metrics Autoscaler Operator overview.

Vertical Pod Autoscaler

The Vertical Pod Autoscaler (VPA) can automatically review the historic and current CPU and memory resources for containers in pods and can update the resource limits and requests based on the usage values it learns.

For more information, see Automatically adjust pod resource levels with the vertical pod autoscaler.

1.5. Glossary of common terms for OpenShift Container Platform nodes

This glossary defines common terms that are used in the node content.

Container
It is a lightweight and executable image that comprises software and all its dependencies. Containers virtualize the operating system, as a result, you can run containers anywhere from a data center to a public or private cloud to even a developer’s laptop.
Daemon set
Ensures that a replica of the pod runs on eligible nodes in an OpenShift Container Platform cluster.
egress
The process of data sharing externally through a network’s outbound traffic from a pod.
garbage collection
The process of cleaning up cluster resources, such as terminated containers and images that are not referenced by any running pods.
Horizontal Pod Autoscaler(HPA)
Implemented as a Kubernetes API resource and a controller. You can use the HPA to specify the minimum and maximum number of pods that you want to run. You can also specify the CPU or memory utilization that your pods should target. The HPA scales out and scales in pods when a given CPU or memory threshold is crossed.
Ingress
Incoming traffic to a pod.
Job
A process that runs to completion. A job creates one or more pod objects and ensures that the specified pods are successfully completed.
Labels
You can use labels, which are key-value pairs, to organise and select subsets of objects, such as a pod.
Node
A worker machine in the OpenShift Container Platform cluster. A node can be either be a virtual machine (VM) or a physical machine.
Node Tuning Operator
You can use the Node Tuning Operator to manage node-level tuning by using the TuneD daemon. It ensures custom tuning specifications are passed to all containerized TuneD daemons running in the cluster in the format that the daemons understand. The daemons run on all nodes in the cluster, one per node.
Self Node Remediation Operator
The Operator runs on the cluster nodes and identifies and reboots nodes that are unhealthy.
Pod
One or more containers with shared resources, such as volume and IP addresses, running in your OpenShift Container Platform cluster. A pod is the smallest compute unit defined, deployed, and managed.
Toleration
Indicates that the pod is allowed (but not required) to be scheduled on nodes or node groups with matching taints. You can use tolerations to enable the scheduler to schedule pods with matching taints.
Taint
A core object that comprises a key,value, and effect. Taints and tolerations work together to ensure that pods are not scheduled on irrelevant nodes.

Chapter 2. Working with pods

2.1. Using pods

A pod is one or more containers deployed together on one host, and the smallest compute unit that can be defined, deployed, and managed.

2.1.1. Understanding pods

Pods are the rough equivalent of a machine instance (physical or virtual) to a Container. Each pod is allocated its own internal IP address, therefore owning its entire port space, and containers within pods can share their local storage and networking.

Pods have a lifecycle; they are defined, then they are assigned to run on a node, then they run until their container(s) exit or they are removed for some other reason. Pods, depending on policy and exit code, might be removed after exiting, or can be retained to enable access to the logs of their containers.

OpenShift Container Platform treats pods as largely immutable; changes cannot be made to a pod definition while it is running. OpenShift Container Platform implements changes by terminating an existing pod and recreating it with modified configuration, base image(s), or both. Pods are also treated as expendable, and do not maintain state when recreated. Therefore pods should usually be managed by higher-level controllers, rather than directly by users.

Note

For the maximum number of pods per OpenShift Container Platform node host, see the Cluster Limits.

Warning

Bare pods that are not managed by a replication controller will be not rescheduled upon node disruption.

2.1.2. Example pod configurations

OpenShift Container Platform leverages the Kubernetes concept of a pod, which is one or more containers deployed together on one host, and the smallest compute unit that can be defined, deployed, and managed.

The following is an example definition of a pod from a Rails application. It demonstrates many features of pods, most of which are discussed in other topics and thus only briefly mentioned here:

Pod object definition (YAML)

kind: Pod
apiVersion: v1
metadata:
  name: example
  namespace: default
  selfLink: /api/v1/namespaces/default/pods/example
  uid: 5cc30063-0265780783bc
  resourceVersion: '165032'
  creationTimestamp: '2019-02-13T20:31:37Z'
  labels:
    app: hello-openshift 1
  annotations:
    openshift.io/scc: anyuid
spec:
  restartPolicy: Always 2
  serviceAccountName: default
  imagePullSecrets:
    - name: default-dockercfg-5zrhb
  priority: 0
  schedulerName: default-scheduler
  terminationGracePeriodSeconds: 30
  nodeName: ip-10-0-140-16.us-east-2.compute.internal
  securityContext: 3
    seLinuxOptions:
      level: 's0:c11,c10'
  containers: 4
    - resources: {}
      terminationMessagePath: /dev/termination-log
      name: hello-openshift
      securityContext:
        capabilities:
          drop:
            - MKNOD
        procMount: Default
      ports:
        - containerPort: 8080
          protocol: TCP
      imagePullPolicy: Always
      volumeMounts: 5
        - name: default-token-wbqsl
          readOnly: true
          mountPath: /var/run/secrets/kubernetes.io/serviceaccount 6
      terminationMessagePolicy: File
      image: registry.redhat.io/openshift4/ose-ogging-eventrouter:v4.3 7
  serviceAccount: default 8
  volumes: 9
    - name: default-token-wbqsl
      secret:
        secretName: default-token-wbqsl
        defaultMode: 420
  dnsPolicy: ClusterFirst
status:
  phase: Pending
  conditions:
    - type: Initialized
      status: 'True'
      lastProbeTime: null
      lastTransitionTime: '2019-02-13T20:31:37Z'
    - type: Ready
      status: 'False'
      lastProbeTime: null
      lastTransitionTime: '2019-02-13T20:31:37Z'
      reason: ContainersNotReady
      message: 'containers with unready status: [hello-openshift]'
    - type: ContainersReady
      status: 'False'
      lastProbeTime: null
      lastTransitionTime: '2019-02-13T20:31:37Z'
      reason: ContainersNotReady
      message: 'containers with unready status: [hello-openshift]'
    - type: PodScheduled
      status: 'True'
      lastProbeTime: null
      lastTransitionTime: '2019-02-13T20:31:37Z'
  hostIP: 10.0.140.16
  startTime: '2019-02-13T20:31:37Z'
  containerStatuses:
    - name: hello-openshift
      state:
        waiting:
          reason: ContainerCreating
      lastState: {}
      ready: false
      restartCount: 0
      image: openshift/hello-openshift
      imageID: ''
  qosClass: BestEffort

1
Pods can be "tagged" with one or more labels, which can then be used to select and manage groups of pods in a single operation. The labels are stored in key/value format in the metadata hash.
2
The pod restart policy with possible values Always, OnFailure, and Never. The default value is Always.
3
OpenShift Container Platform defines a security context for containers which specifies whether they are allowed to run as privileged containers, run as a user of their choice, and more. The default context is very restrictive but administrators can modify this as needed.
4
containers specifies an array of one or more container definitions.
5
The container specifies where external storage volumes are mounted within the container. In this case, there is a volume for storing access to credentials the registry needs for making requests against the OpenShift Container Platform API.
6
Specify the volumes to provide for the pod. Volumes mount at the specified path. Do not mount to the container root, /, or any path that is the same in the host and the container. This can corrupt your host system if the container is sufficiently privileged, such as the host /dev/pts files. It is safe to mount the host by using /host.
7
Each container in the pod is instantiated from its own container image.
8
Pods making requests against the OpenShift Container Platform API is a common enough pattern that there is a serviceAccount field for specifying which service account user the pod should authenticate as when making the requests. This enables fine-grained access control for custom infrastructure components.
9
The pod defines storage volumes that are available to its container(s) to use. In this case, it provides an ephemeral volume for a secret volume containing the default service account tokens.

If you attach persistent volumes that have high file counts to pods, those pods can fail or can take a long time to start. For more information, see When using Persistent Volumes with high file counts in OpenShift, why do pods fail to start or take an excessive amount of time to achieve "Ready" state?.

Note

This pod definition does not include attributes that are filled by OpenShift Container Platform automatically after the pod is created and its lifecycle begins. The Kubernetes pod documentation has details about the functionality and purpose of pods.

2.1.3. Additional resources

2.2. Viewing pods

As an administrator, you can view the pods in your cluster and to determine the health of those pods and the cluster as a whole.

2.2.1. About pods

OpenShift Container Platform leverages the Kubernetes concept of a pod, which is one or more containers deployed together on one host, and the smallest compute unit that can be defined, deployed, and managed. Pods are the rough equivalent of a machine instance (physical or virtual) to a container.

You can view a list of pods associated with a specific project or view usage statistics about pods.

2.2.2. Viewing pods in a project

You can view a list of pods associated with the current project, including the number of replica, the current status, number or restarts and the age of the pod.

Procedure

To view the pods in a project:

  1. Change to the project:

    $ oc project <project-name>
  2. Run the following command:

    $ oc get pods

    For example:

    $ oc get pods

    Example output

    NAME                       READY   STATUS    RESTARTS   AGE
    console-698d866b78-bnshf   1/1     Running   2          165m
    console-698d866b78-m87pm   1/1     Running   2          165m

    Add the -o wide flags to view the pod IP address and the node where the pod is located.

    $ oc get pods -o wide

    Example output

    NAME                       READY   STATUS    RESTARTS   AGE    IP            NODE                           NOMINATED NODE
    console-698d866b78-bnshf   1/1     Running   2          166m   10.128.0.24   ip-10-0-152-71.ec2.internal    <none>
    console-698d866b78-m87pm   1/1     Running   2          166m   10.129.0.23   ip-10-0-173-237.ec2.internal   <none>

2.2.3. Viewing pod usage statistics

You can display usage statistics about pods, which provide the runtime environments for containers. These usage statistics include CPU, memory, and storage consumption.

Prerequisites

  • You must have cluster-reader permission to view the usage statistics.
  • Metrics must be installed to view the usage statistics.

Procedure

To view the usage statistics:

  1. Run the following command:

    $ oc adm top pods

    For example:

    $ oc adm top pods -n openshift-console

    Example output

    NAME                         CPU(cores)   MEMORY(bytes)
    console-7f58c69899-q8c8k     0m           22Mi
    console-7f58c69899-xhbgg     0m           25Mi
    downloads-594fcccf94-bcxk8   3m           18Mi
    downloads-594fcccf94-kv4p6   2m           15Mi

  2. Run the following command to view the usage statistics for pods with labels:

    $ oc adm top pod --selector=''

    You must choose the selector (label query) to filter on. Supports =, ==, and !=.

    For example:

    $ oc adm top pod --selector='name=my-pod'

2.2.4. Viewing resource logs

You can view the log for various resources in the OpenShift CLI (oc) and web console. Logs read from the tail, or end, of the log.

Prerequisites

  • Access to the OpenShift CLI (oc).

Procedure (UI)

  1. In the OpenShift Container Platform console, navigate to WorkloadsPods or navigate to the pod through the resource you want to investigate.

    Note

    Some resources, such as builds, do not have pods to query directly. In such instances, you can locate the Logs link on the Details page for the resource.

  2. Select a project from the drop-down menu.
  3. Click the name of the pod you want to investigate.
  4. Click Logs.

Procedure (CLI)

  • View the log for a specific pod:

    $ oc logs -f <pod_name> -c <container_name>

    where:

    -f
    Optional: Specifies that the output follows what is being written into the logs.
    <pod_name>
    Specifies the name of the pod.
    <container_name>
    Optional: Specifies the name of a container. When a pod has more than one container, you must specify the container name.

    For example:

    $ oc logs ruby-58cd97df55-mww7r
    $ oc logs -f ruby-57f7f4855b-znl92 -c ruby

    The contents of log files are printed out.

  • View the log for a specific resource:

    $ oc logs <object_type>/<resource_name> 1
    1
    Specifies the resource type and name.

    For example:

    $ oc logs deployment/ruby

    The contents of log files are printed out.

2.3. Configuring an OpenShift Container Platform cluster for pods

As an administrator, you can create and maintain an efficient cluster for pods.

By keeping your cluster efficient, you can provide a better environment for your developers using such tools as what a pod does when it exits, ensuring that the required number of pods is always running, when to restart pods designed to run only once, limit the bandwidth available to pods, and how to keep pods running during disruptions.

2.3.1. Configuring how pods behave after restart

A pod restart policy determines how OpenShift Container Platform responds when Containers in that pod exit. The policy applies to all Containers in that pod.

The possible values are:

  • Always - Tries restarting a successfully exited Container on the pod continuously, with an exponential back-off delay (10s, 20s, 40s) capped at 5 minutes. The default is Always.
  • OnFailure - Tries restarting a failed Container on the pod with an exponential back-off delay (10s, 20s, 40s) capped at 5 minutes.
  • Never - Does not try to restart exited or failed Containers on the pod. Pods immediately fail and exit.

After the pod is bound to a node, the pod will never be bound to another node. This means that a controller is necessary in order for a pod to survive node failure:

ConditionController TypeRestart Policy

Pods that are expected to terminate (such as batch computations)

Job

OnFailure or Never

Pods that are expected to not terminate (such as web servers)

Replication controller

Always.

Pods that must run one-per-machine

Daemon set

Any

If a Container on a pod fails and the restart policy is set to OnFailure, the pod stays on the node and the Container is restarted. If you do not want the Container to restart, use a restart policy of Never.

If an entire pod fails, OpenShift Container Platform starts a new pod. Developers must address the possibility that applications might be restarted in a new pod. In particular, applications must handle temporary files, locks, incomplete output, and so forth caused by previous runs.

Note

Kubernetes architecture expects reliable endpoints from cloud providers. When a cloud provider is down, the kubelet prevents OpenShift Container Platform from restarting.

If the underlying cloud provider endpoints are not reliable, do not install a cluster using cloud provider integration. Install the cluster as if it was in a no-cloud environment. It is not recommended to toggle cloud provider integration on or off in an installed cluster.

For details on how OpenShift Container Platform uses restart policy with failed Containers, see the Example States in the Kubernetes documentation.

2.3.2. Limiting the bandwidth available to pods

You can apply quality-of-service traffic shaping to a pod and effectively limit its available bandwidth. Egress traffic (from the pod) is handled by policing, which simply drops packets in excess of the configured rate. Ingress traffic (to the pod) is handled by shaping queued packets to effectively handle data. The limits you place on a pod do not affect the bandwidth of other pods.

Procedure

To limit the bandwidth on a pod:

  1. Write an object definition JSON file, and specify the data traffic speed using kubernetes.io/ingress-bandwidth and kubernetes.io/egress-bandwidth annotations. For example, to limit both pod egress and ingress bandwidth to 10M/s:

    Limited Pod object definition

    {
        "kind": "Pod",
        "spec": {
            "containers": [
                {
                    "image": "openshift/hello-openshift",
                    "name": "hello-openshift"
                }
            ]
        },
        "apiVersion": "v1",
        "metadata": {
            "name": "iperf-slow",
            "annotations": {
                "kubernetes.io/ingress-bandwidth": "10M",
                "kubernetes.io/egress-bandwidth": "10M"
            }
        }
    }

  2. Create the pod using the object definition:

    $ oc create -f <file_or_dir_path>

2.3.3. Understanding how to use pod disruption budgets to specify the number of pods that must be up

A pod disruption budget allows the specification of safety constraints on pods during operations, such as draining a node for maintenance.

PodDisruptionBudget is an API object that specifies the minimum number or percentage of replicas that must be up at a time. Setting these in projects can be helpful during node maintenance (such as scaling a cluster down or a cluster upgrade) and is only honored on voluntary evictions (not on node failures).

A PodDisruptionBudget object’s configuration consists of the following key parts:

  • A label selector, which is a label query over a set of pods.
  • An availability level, which specifies the minimum number of pods that must be available simultaneously, either:

    • minAvailable is the number of pods must always be available, even during a disruption.
    • maxUnavailable is the number of pods can be unavailable during a disruption.
Note

Available refers to the number of pods that has condition Ready=True. Ready=True refers to the pod that is able to serve requests and should be added to the load balancing pools of all matching services.

A maxUnavailable of 0% or 0 or a minAvailable of 100% or equal to the number of replicas is permitted but can block nodes from being drained.

You can check for pod disruption budgets across all projects with the following:

$ oc get poddisruptionbudget --all-namespaces

Example output

NAMESPACE                              NAME                                    MIN AVAILABLE   MAX UNAVAILABLE   ALLOWED DISRUPTIONS   AGE
openshift-apiserver                    openshift-apiserver-pdb                 N/A             1                 1                     121m
openshift-cloud-controller-manager     aws-cloud-controller-manager            1               N/A               1                     125m
openshift-cloud-credential-operator    pod-identity-webhook                    1               N/A               1                     117m
openshift-cluster-csi-drivers          aws-ebs-csi-driver-controller-pdb       N/A             1                 1                     121m
openshift-cluster-storage-operator     csi-snapshot-controller-pdb             N/A             1                 1                     122m
openshift-cluster-storage-operator     csi-snapshot-webhook-pdb                N/A             1                 1                     122m
openshift-console                      console                                 N/A             1                 1                     116m
#...

The PodDisruptionBudget is considered healthy when there are at least minAvailable pods running in the system. Every pod above that limit can be evicted.

Note

Depending on your pod priority and preemption settings, lower-priority pods might be removed despite their pod disruption budget requirements.

2.3.3.1. Specifying the number of pods that must be up with pod disruption budgets

You can use a PodDisruptionBudget object to specify the minimum number or percentage of replicas that must be up at a time.

Procedure

To configure a pod disruption budget:

  1. Create a YAML file with the an object definition similar to the following:

    apiVersion: policy/v1 1
    kind: PodDisruptionBudget
    metadata:
      name: my-pdb
    spec:
      minAvailable: 2  2
      selector:  3
        matchLabels:
          name: my-pod
    1
    PodDisruptionBudget is part of the policy/v1 API group.
    2
    The minimum number of pods that must be available simultaneously. This can be either an integer or a string specifying a percentage, for example, 20%.
    3
    A label query over a set of resources. The result of matchLabels and matchExpressions are logically conjoined. Leave this paramter blank, for example selector {}, to select all pods in the project.

    Or:

    apiVersion: policy/v1 1
    kind: PodDisruptionBudget
    metadata:
      name: my-pdb
    spec:
      maxUnavailable: 25% 2
      selector: 3
        matchLabels:
          name: my-pod
    1
    PodDisruptionBudget is part of the policy/v1 API group.
    2
    The maximum number of pods that can be unavailable simultaneously. This can be either an integer or a string specifying a percentage, for example, 20%.
    3
    A label query over a set of resources. The result of matchLabels and matchExpressions are logically conjoined. Leave this paramter blank, for example selector {}, to select all pods in the project.
  2. Run the following command to add the object to project:

    $ oc create -f </path/to/file> -n <project_name>

2.3.4. Preventing pod removal using critical pods

There are a number of core components that are critical to a fully functional cluster, but, run on a regular cluster node rather than the master. A cluster might stop working properly if a critical add-on is evicted.

Pods marked as critical are not allowed to be evicted.

Procedure

To make a pod critical:

  1. Create a Pod spec or edit existing pods to include the system-cluster-critical priority class:

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pdb
    spec:
      template:
        metadata:
          name: critical-pod
        priorityClassName: system-cluster-critical 1
    1
    Default priority class for pods that should never be evicted from a node.

    Alternatively, you can specify system-node-critical for pods that are important to the cluster but can be removed if necessary.

  2. Create the pod:

    $ oc create -f <file-name>.yaml

2.3.5. Reducing pod timeouts when using persistent volumes with high file counts

If a storage volume contains many files (~1,000,000 or greater), you might experience pod timeouts.

This can occur because, when volumes are mounted, OpenShift Container Platform recursively changes the ownership and permissions of the contents of each volume in order to match the fsGroup specified in a pod’s securityContext. For large volumes, checking and changing the ownership and permissions can be time consuming, resulting in a very slow pod startup.

You can reduce this delay by applying one of the following workarounds:

  • Use a security context constraint (SCC) to skip the SELinux relabeling for a volume.
  • Use the fsGroupChangePolicy field inside an SCC to control the way that OpenShift Container Platform checks and manages ownership and permissions for a volume.
  • Use a runtime class to skip the SELinux relabeling for a volume.

For information, see When using Persistent Volumes with high file counts in OpenShift, why do pods fail to start or take an excessive amount of time to achieve "Ready" state?.

2.4. Automatically scaling pods with the horizontal pod autoscaler

As a developer, you can use a horizontal pod autoscaler (HPA) to specify how OpenShift Container Platform should automatically increase or decrease the scale of a replication controller or deployment configuration, based on metrics collected from the pods that belong to that replication controller or deployment configuration. You can create an HPA for any deployment, deployment config, replica set, replication controller, or stateful set.

For information on scaling pods based on custom metrics, see Automatically scaling pods based on custom metrics.

Note

It is recommended to use a Deployment object or ReplicaSet object unless you need a specific feature or behavior provided by other objects. For more information on these objects, see Understanding Deployment and DeploymentConfig objects.

2.4.1. Understanding horizontal pod autoscalers

You can create a horizontal pod autoscaler to specify the minimum and maximum number of pods you want to run, as well as the CPU utilization or memory utilization your pods should target.

After you create a horizontal pod autoscaler, OpenShift Container Platform begins to query the CPU and/or memory resource metrics on the pods. When these metrics are available, the horizontal pod autoscaler computes the ratio of the current metric utilization with the desired metric utilization, and scales up or down accordingly. The query and scaling occurs at a regular interval, but can take one to two minutes before metrics become available.

For replication controllers, this scaling corresponds directly to the replicas of the replication controller. For deployment configurations, scaling corresponds directly to the replica count of the deployment configuration. Note that autoscaling applies only to the latest deployment in the Complete phase.

OpenShift Container Platform automatically accounts for resources and prevents unnecessary autoscaling during resource spikes, such as during start up. Pods in the unready state have 0 CPU usage when scaling up and the autoscaler ignores the pods when scaling down. Pods without known metrics have 0% CPU usage when scaling up and 100% CPU when scaling down. This allows for more stability during the HPA decision. To use this feature, you must configure readiness checks to determine if a new pod is ready for use.

To use horizontal pod autoscalers, your cluster administrator must have properly configured cluster metrics.

2.4.1.1. Supported metrics

The following metrics are supported by horizontal pod autoscalers:

Table 2.1. Metrics
MetricDescriptionAPI version

CPU utilization

Number of CPU cores used. Can be used to calculate a percentage of the pod’s requested CPU.

autoscaling/v1, autoscaling/v2

Memory utilization

Amount of memory used. Can be used to calculate a percentage of the pod’s requested memory.

autoscaling/v2

Important

For memory-based autoscaling, memory usage must increase and decrease proportionally to the replica count. On average:

  • An increase in replica count must lead to an overall decrease in memory (working set) usage per-pod.
  • A decrease in replica count must lead to an overall increase in per-pod memory usage.

Use the OpenShift Container Platform web console to check the memory behavior of your application and ensure that your application meets these requirements before using memory-based autoscaling.

The following example shows autoscaling for the image-registry Deployment object. The initial deployment requires 3 pods. The HPA object increases the minimum to 5. If CPU usage on the pods reaches 75%, the pods increase to 7:

$ oc autoscale deployment/image-registry --min=5 --max=7 --cpu-percent=75

Example output

horizontalpodautoscaler.autoscaling/image-registry autoscaled

Sample HPA for the image-registry Deployment object with minReplicas set to 3

apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
  name: image-registry
  namespace: default
spec:
  maxReplicas: 7
  minReplicas: 3
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: image-registry
  targetCPUUtilizationPercentage: 75
status:
  currentReplicas: 5
  desiredReplicas: 0

  1. View the new state of the deployment:

    $ oc get deployment image-registry

    There are now 5 pods in the deployment:

    Example output

    NAME             REVISION   DESIRED   CURRENT   TRIGGERED BY
    image-registry   1          5         5         config

2.4.2. How does the HPA work?

The horizontal pod autoscaler (HPA) extends the concept of pod auto-scaling. The HPA lets you create and manage a group of load-balanced nodes. The HPA automatically increases or decreases the number of pods when a given CPU or memory threshold is crossed.

Figure 2.1. High level workflow of the HPA

workflow

The HPA is an API resource in the Kubernetes autoscaling API group. The autoscaler works as a control loop with a default of 15 seconds for the sync period. During this period, the controller manager queries the CPU, memory utilization, or both, against what is defined in the YAML file for the HPA. The controller manager obtains the utilization metrics from the resource metrics API for per-pod resource metrics like CPU or memory, for each pod that is targeted by the HPA.

If a utilization value target is set, the controller calculates the utilization value as a percentage of the equivalent resource request on the containers in each pod. The controller then takes the average of utilization across all targeted pods and produces a ratio that is used to scale the number of desired replicas. The HPA is configured to fetch metrics from metrics.k8s.io, which is provided by the metrics server. Because of the dynamic nature of metrics evaluation, the number of replicas can fluctuate during scaling for a group of replicas.

Note

To implement the HPA, all targeted pods must have a resource request set on their containers.

2.4.3. About requests and limits

The scheduler uses the resource request that you specify for containers in a pod, to decide which node to place the pod on. The kubelet enforces the resource limit that you specify for a container to ensure that the container is not allowed to use more than the specified limit. The kubelet also reserves the request amount of that system resource specifically for that container to use.

How to use resource metrics?

In the pod specifications, you must specify the resource requests, such as CPU and memory. The HPA uses this specification to determine the resource utilization and then scales the target up or down.

For example, the HPA object uses the following metric source:

type: Resource
resource:
  name: cpu
  target:
    type: Utilization
    averageUtilization: 60

In this example, the HPA keeps the average utilization of the pods in the scaling target at 60%. Utilization is the ratio between the current resource usage to the requested resource of the pod.

2.4.4. Best practices

All pods must have resource requests configured

The HPA makes a scaling decision based on the observed CPU or memory utilization values of pods in an OpenShift Container Platform cluster. Utilization values are calculated as a percentage of the resource requests of each pod. Missing resource request values can affect the optimal performance of the HPA.

Configure the cool down period

During horizontal pod autoscaling, there might be a rapid scaling of events without a time gap. Configure the cool down period to prevent frequent replica fluctuations. You can specify a cool down period by configuring the stabilizationWindowSeconds field. The stabilization window is used to restrict the fluctuation of replicas count when the metrics used for scaling keep fluctuating. The autoscaling algorithm uses this window to infer a previous desired state and avoid unwanted changes to workload scale.

For example, a stabilization window is specified for the scaleDown field:

behavior:
  scaleDown:
    stabilizationWindowSeconds: 300

In the above example, all desired states for the past 5 minutes are considered. This approximates a rolling maximum, and avoids having the scaling algorithm frequently remove pods only to trigger recreating an equivalent pod just moments later.

2.4.4.1. Scaling policies

The autoscaling/v2 API allows you to add scaling policies to a horizontal pod autoscaler. A scaling policy controls how the OpenShift Container Platform horizontal pod autoscaler (HPA) scales pods. Scaling policies allow you to restrict the rate that HPAs scale pods up or down by setting a specific number or specific percentage to scale in a specified period of time. You can also define a stabilization window, which uses previously computed desired states to control scaling if the metrics are fluctuating. You can create multiple policies for the same scaling direction, and determine which policy is used, based on the amount of change. You can also restrict the scaling by timed iterations. The HPA scales pods during an iteration, then performs scaling, as needed, in further iterations.

Sample HPA object with a scaling policy

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: hpa-resource-metrics-memory
  namespace: default
spec:
  behavior:
    scaleDown: 1
      policies: 2
      - type: Pods 3
        value: 4 4
        periodSeconds: 60 5
      - type: Percent
        value: 10 6
        periodSeconds: 60
      selectPolicy: Min 7
      stabilizationWindowSeconds: 300 8
    scaleUp: 9
      policies:
      - type: Pods
        value: 5 10
        periodSeconds: 70
      - type: Percent
        value: 12 11
        periodSeconds: 80
      selectPolicy: Max
      stabilizationWindowSeconds: 0
...

1
Specifies the direction for the scaling policy, either scaleDown or scaleUp. This example creates a policy for scaling down.
2
Defines the scaling policy.
3
Determines if the policy scales by a specific number of pods or a percentage of pods during each iteration. The default value is pods.
4
Limits the amount of scaling, either the number of pods or percentage of pods, during each iteration. There is no default value for scaling down by number of pods.
5
Determines the length of a scaling iteration. The default value is 15 seconds.
6
The default value for scaling down by percentage is 100%.
7
Determines which policy to use first, if multiple policies are defined. Specify Max to use the policy that allows the highest amount of change, Min to use the policy that allows the lowest amount of change, or Disabled to prevent the HPA from scaling in that policy direction. The default value is Max.
8
Determines the time period the HPA should look back at desired states. The default value is 0.
9
This example creates a policy for scaling up.
10
Limits the amount of scaling up by the number of pods. The default value for scaling up the number of pods is 4%.
11
Limits the amount of scaling up by the percentage of pods. The default value for scaling up by percentage is 100%.

Example policy for scaling down

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: hpa-resource-metrics-memory
  namespace: default
spec:
...
  minReplicas: 20
...
  behavior:
    scaleDown:
      stabilizationWindowSeconds: 300
      policies:
      - type: Pods
        value: 4
        periodSeconds: 30
      - type: Percent
        value: 10
        periodSeconds: 60
      selectPolicy: Max
    scaleUp:
      selectPolicy: Disabled

In this example, when the number of pods is greater than 40, the percent-based policy is used for scaling down, as that policy results in a larger change, as required by the selectPolicy.

If there are 80 pod replicas, in the first iteration the HPA reduces the pods by 8, which is 10% of the 80 pods (based on the type: Percent and value: 10 parameters), over one minute (periodSeconds: 60). For the next iteration, the number of pods is 72. The HPA calculates that 10% of the remaining pods is 7.2, which it rounds up to 8 and scales down 8 pods. On each subsequent iteration, the number of pods to be scaled is re-calculated based on the number of remaining pods. When the number of pods falls below 40, the pods-based policy is applied, because the pod-based number is greater than the percent-based number. The HPA reduces 4 pods at a time (type: Pods and value: 4), over 30 seconds (periodSeconds: 30), until there are 20 replicas remaining (minReplicas).

The selectPolicy: Disabled parameter prevents the HPA from scaling up the pods. You can manually scale up by adjusting the number of replicas in the replica set or deployment set, if needed.

If set, you can view the scaling policy by using the oc edit command:

$ oc edit hpa hpa-resource-metrics-memory

Example output

apiVersion: autoscaling/v1
kind: HorizontalPodAutoscaler
metadata:
  annotations:
    autoscaling.alpha.kubernetes.io/behavior:\
'{"ScaleUp":{"StabilizationWindowSeconds":0,"SelectPolicy":"Max","Policies":[{"Type":"Pods","Value":4,"PeriodSeconds":15},{"Type":"Percent","Value":100,"PeriodSeconds":15}]},\
"ScaleDown":{"StabilizationWindowSeconds":300,"SelectPolicy":"Min","Policies":[{"Type":"Pods","Value":4,"PeriodSeconds":60},{"Type":"Percent","Value":10,"PeriodSeconds":60}]}}'
...

2.4.5. Creating a horizontal pod autoscaler by using the web console

From the web console, you can create a horizontal pod autoscaler (HPA) that specifies the minimum and maximum number of pods you want to run on a Deployment or DeploymentConfig object. You can also define the amount of CPU or memory usage that your pods should target.

Note

An HPA cannot be added to deployments that are part of an Operator-backed service, Knative service, or Helm chart.

Procedure

To create an HPA in the web console:

  1. In the Topology view, click the node to reveal the side pane.
  2. From the Actions drop-down list, select Add HorizontalPodAutoscaler to open the Add HorizontalPodAutoscaler form.

    Figure 2.2. Add HorizontalPodAutoscaler

    Add HorizontalPodAutoscaler form
  3. From the Add HorizontalPodAutoscaler form, define the name, minimum and maximum pod limits, the CPU and memory usage, and click Save.

    Note

    If any of the values for CPU and memory usage are missing, a warning is displayed.

To edit an HPA in the web console:

  1. In the Topology view, click the node to reveal the side pane.
  2. From the Actions drop-down list, select Edit HorizontalPodAutoscaler to open the Edit Horizontal Pod Autoscaler form.
  3. From the Edit Horizontal Pod Autoscaler form, edit the minimum and maximum pod limits and the CPU and memory usage, and click Save.
Note

While creating or editing the horizontal pod autoscaler in the web console, you can switch from Form view to YAML view.

To remove an HPA in the web console:

  1. In the Topology view, click the node to reveal the side panel.
  2. From the Actions drop-down list, select Remove HorizontalPodAutoscaler.
  3. In the confirmation pop-up window, click Remove to remove the HPA.

2.4.6. Creating a horizontal pod autoscaler for CPU utilization by using the CLI

Using the OpenShift Container Platform CLI, you can create a horizontal pod autoscaler (HPA) to automatically scale an existing Deployment, DeploymentConfig, ReplicaSet, ReplicationController, or StatefulSet object. The HPA scales the pods associated with that object to maintain the CPU usage you specify.

Note

It is recommended to use a Deployment object or ReplicaSet object unless you need a specific feature or behavior provided by other objects.

The HPA increases and decreases the number of replicas between the minimum and maximum numbers to maintain the specified CPU utilization across all pods.

When autoscaling for CPU utilization, you can use the oc autoscale command and specify the minimum and maximum number of pods you want to run at any given time and the average CPU utilization your pods should target. If you do not specify a minimum, the pods are given default values from the OpenShift Container Platform server.

To autoscale for a specific CPU value, create a HorizontalPodAutoscaler object with the target CPU and pod limits.

Prerequisites

To use horizontal pod autoscalers, your cluster administrator must have properly configured cluster metrics. You can use the oc describe PodMetrics <pod-name> command to determine if metrics are configured. If metrics are configured, the output appears similar to the following, with Cpu and Memory displayed under Usage.

$ oc describe PodMetrics openshift-kube-scheduler-ip-10-0-135-131.ec2.internal

Example output

Name:         openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Namespace:    openshift-kube-scheduler
Labels:       <none>
Annotations:  <none>
API Version:  metrics.k8s.io/v1beta1
Containers:
  Name:  wait-for-host-port
  Usage:
    Memory:  0
  Name:      scheduler
  Usage:
    Cpu:     8m
    Memory:  45440Ki
Kind:        PodMetrics
Metadata:
  Creation Timestamp:  2019-05-23T18:47:56Z
  Self Link:           /apis/metrics.k8s.io/v1beta1/namespaces/openshift-kube-scheduler/pods/openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Timestamp:             2019-05-23T18:47:56Z
Window:                1m0s
Events:                <none>

Procedure

To create a horizontal pod autoscaler for CPU utilization:

  1. Perform one of the following:

    • To scale based on the percent of CPU utilization, create a HorizontalPodAutoscaler object for an existing object:

      $ oc autoscale <object_type>/<name> \1
        --min <number> \2
        --max <number> \3
        --cpu-percent=<percent> 4
      1
      Specify the type and name of the object to autoscale. The object must exist and be a Deployment, DeploymentConfig/dc, ReplicaSet/rs, ReplicationController/rc, or StatefulSet.
      2
      Optionally, specify the minimum number of replicas when scaling down.
      3
      Specify the maximum number of replicas when scaling up.
      4
      Specify the target average CPU utilization over all the pods, represented as a percent of requested CPU. If not specified or negative, a default autoscaling policy is used.

      For example, the following command shows autoscaling for the image-registry Deployment object. The initial deployment requires 3 pods. The HPA object increases the minimum to 5. If CPU usage on the pods reaches 75%, the pods will increase to 7:

      $ oc autoscale deployment/image-registry --min=5 --max=7 --cpu-percent=75
    • To scale for a specific CPU value, create a YAML file similar to the following for an existing object:

      1. Create a YAML file similar to the following:

        apiVersion: autoscaling/v2 1
        kind: HorizontalPodAutoscaler
        metadata:
          name: cpu-autoscale 2
          namespace: default
        spec:
          scaleTargetRef:
            apiVersion: apps/v1 3
            kind: Deployment 4
            name: example 5
          minReplicas: 1 6
          maxReplicas: 10 7
          metrics: 8
          - type: Resource
            resource:
              name: cpu 9
              target:
                type: AverageValue 10
                averageValue: 500m 11
        1
        Use the autoscaling/v2 API.
        2
        Specify a name for this horizontal pod autoscaler object.
        3
        Specify the API version of the object to scale:
        • For a Deployment, ReplicaSet, Statefulset object, use apps/v1.
        • For a ReplicationController, use v1.
        • For a DeploymentConfig, use apps.openshift.io/v1.
        4
        Specify the type of object. The object must be a Deployment, DeploymentConfig/dc, ReplicaSet/rs, ReplicationController/rc, or StatefulSet.
        5
        Specify the name of the object to scale. The object must exist.
        6
        Specify the minimum number of replicas when scaling down.
        7
        Specify the maximum number of replicas when scaling up.
        8
        Use the metrics parameter for memory utilization.
        9
        Specify cpu for CPU utilization.
        10
        Set to AverageValue.
        11
        Set to averageValue with the targeted CPU value.
      2. Create the horizontal pod autoscaler:

        $ oc create -f <file-name>.yaml
  2. Verify that the horizontal pod autoscaler was created:

    $ oc get hpa cpu-autoscale

    Example output

    NAME            REFERENCE            TARGETS         MINPODS   MAXPODS   REPLICAS   AGE
    cpu-autoscale   Deployment/example   173m/500m       1         10        1          20m

2.4.7. Creating a horizontal pod autoscaler object for memory utilization by using the CLI

Using the OpenShift Container Platform CLI, you can create a horizontal pod autoscaler (HPA) to automatically scale an existing Deployment, DeploymentConfig, ReplicaSet, ReplicationController, or StatefulSet object. The HPA scales the pods associated with that object to maintain the average memory utilization you specify, either a direct value or a percentage of requested memory.

Note

It is recommended to use a Deployment object or ReplicaSet object unless you need a specific feature or behavior provided by other objects.

The HPA increases and decreases the number of replicas between the minimum and maximum numbers to maintain the specified memory utilization across all pods.

For memory utilization, you can specify the minimum and maximum number of pods and the average memory utilization your pods should target. If you do not specify a minimum, the pods are given default values from the OpenShift Container Platform server.

Prerequisites

To use horizontal pod autoscalers, your cluster administrator must have properly configured cluster metrics. You can use the oc describe PodMetrics <pod-name> command to determine if metrics are configured. If metrics are configured, the output appears similar to the following, with Cpu and Memory displayed under Usage.

$ oc describe PodMetrics openshift-kube-scheduler-ip-10-0-129-223.compute.internal -n openshift-kube-scheduler

Example output

Name:         openshift-kube-scheduler-ip-10-0-129-223.compute.internal
Namespace:    openshift-kube-scheduler
Labels:       <none>
Annotations:  <none>
API Version:  metrics.k8s.io/v1beta1
Containers:
  Name:  wait-for-host-port
  Usage:
    Cpu:     0
    Memory:  0
  Name:      scheduler
  Usage:
    Cpu:     8m
    Memory:  45440Ki
Kind:        PodMetrics
Metadata:
  Creation Timestamp:  2020-02-14T22:21:14Z
  Self Link:           /apis/metrics.k8s.io/v1beta1/namespaces/openshift-kube-scheduler/pods/openshift-kube-scheduler-ip-10-0-129-223.compute.internal
Timestamp:             2020-02-14T22:21:14Z
Window:                5m0s
Events:                <none>

Procedure

To create a horizontal pod autoscaler for memory utilization:

  1. Create a YAML file for one of the following:

    • To scale for a specific memory value, create a HorizontalPodAutoscaler object similar to the following for an existing object:

      apiVersion: autoscaling/v2 1
      kind: HorizontalPodAutoscaler
      metadata:
        name: hpa-resource-metrics-memory 2
        namespace: default
      spec:
        scaleTargetRef:
          apiVersion: apps/v1 3
          kind: Deployment 4
          name: example 5
        minReplicas: 1 6
        maxReplicas: 10 7
        metrics: 8
        - type: Resource
          resource:
            name: memory 9
            target:
              type: AverageValue 10
              averageValue: 500Mi 11
        behavior: 12
          scaleDown:
            stabilizationWindowSeconds: 300
            policies:
            - type: Pods
              value: 4
              periodSeconds: 60
            - type: Percent
              value: 10
              periodSeconds: 60
            selectPolicy: Max
      1
      Use the autoscaling/v2 API.
      2
      Specify a name for this horizontal pod autoscaler object.
      3
      Specify the API version of the object to scale:
      • For a Deployment, ReplicaSet, or Statefulset object, use apps/v1.
      • For a ReplicationController, use v1.
      • For a DeploymentConfig, use apps.openshift.io/v1.
      4
      Specify the type of object. The object must be a Deployment, DeploymentConfig, ReplicaSet, ReplicationController, or StatefulSet.
      5
      Specify the name of the object to scale. The object must exist.
      6
      Specify the minimum number of replicas when scaling down.
      7
      Specify the maximum number of replicas when scaling up.
      8
      Use the metrics parameter for memory utilization.
      9
      Specify memory for memory utilization.
      10
      Set the type to AverageValue.
      11
      Specify averageValue and a specific memory value.
      12
      Optional: Specify a scaling policy to control the rate of scaling up or down.
    • To scale for a percentage, create a HorizontalPodAutoscaler object similar to the following for an existing object:

      apiVersion: autoscaling/v2 1
      kind: HorizontalPodAutoscaler
      metadata:
        name: memory-autoscale 2
        namespace: default
      spec:
        scaleTargetRef:
          apiVersion: apps/v1 3
          kind: Deployment 4
          name: example 5
        minReplicas: 1 6
        maxReplicas: 10 7
        metrics: 8
        - type: Resource
          resource:
            name: memory 9
            target:
              type: Utilization 10
              averageUtilization: 50 11
        behavior: 12
          scaleUp:
            stabilizationWindowSeconds: 180
            policies:
            - type: Pods
              value: 6
              periodSeconds: 120
            - type: Percent
              value: 10
              periodSeconds: 120
            selectPolicy: Max
      1
      Use the autoscaling/v2 API.
      2
      Specify a name for this horizontal pod autoscaler object.
      3
      Specify the API version of the object to scale:
      • For a ReplicationController, use v1.
      • For a DeploymentConfig, use apps.openshift.io/v1.
      • For a Deployment, ReplicaSet, Statefulset object, use apps/v1.
      4
      Specify the type of object. The object must be a Deployment, DeploymentConfig, ReplicaSet, ReplicationController, or StatefulSet.
      5
      Specify the name of the object to scale. The object must exist.
      6
      Specify the minimum number of replicas when scaling down.
      7
      Specify the maximum number of replicas when scaling up.
      8
      Use the metrics parameter for memory utilization.
      9
      Specify memory for memory utilization.
      10
      Set to Utilization.
      11
      Specify averageUtilization and a target average memory utilization over all the pods, represented as a percent of requested memory. The target pods must have memory requests configured.
      12
      Optional: Specify a scaling policy to control the rate of scaling up or down.
  2. Create the horizontal pod autoscaler:

    $ oc create -f <file-name>.yaml

    For example:

    $ oc create -f hpa.yaml

    Example output

    horizontalpodautoscaler.autoscaling/hpa-resource-metrics-memory created

  3. Verify that the horizontal pod autoscaler was created:

    $ oc get hpa hpa-resource-metrics-memory

    Example output

    NAME                          REFERENCE            TARGETS         MINPODS   MAXPODS   REPLICAS   AGE
    hpa-resource-metrics-memory   Deployment/example   2441216/500Mi   1         10        1          20m

    $ oc describe hpa hpa-resource-metrics-memory

    Example output

    Name:                        hpa-resource-metrics-memory
    Namespace:                   default
    Labels:                      <none>
    Annotations:                 <none>
    CreationTimestamp:           Wed, 04 Mar 2020 16:31:37 +0530
    Reference:                   Deployment/example
    Metrics:                     ( current / target )
      resource memory on pods:   2441216 / 500Mi
    Min replicas:                1
    Max replicas:                10
    ReplicationController pods:  1 current / 1 desired
    Conditions:
      Type            Status  Reason              Message
      ----            ------  ------              -------
      AbleToScale     True    ReadyForNewScale    recommended size matches current size
      ScalingActive   True    ValidMetricFound    the HPA was able to successfully calculate a replica count from memory resource
      ScalingLimited  False   DesiredWithinRange  the desired count is within the acceptable range
    Events:
      Type     Reason                   Age                 From                       Message
      ----     ------                   ----                ----                       -------
      Normal   SuccessfulRescale        6m34s               horizontal-pod-autoscaler  New size: 1; reason: All metrics below target

2.4.8. Understanding horizontal pod autoscaler status conditions by using the CLI

You can use the status conditions set to determine whether or not the horizontal pod autoscaler (HPA) is able to scale and whether or not it is currently restricted in any way.

The HPA status conditions are available with the v2 version of the autoscaling API.

The HPA responds with the following status conditions:

  • The AbleToScale condition indicates whether HPA is able to fetch and update metrics, as well as whether any backoff-related conditions could prevent scaling.

    • A True condition indicates scaling is allowed.
    • A False condition indicates scaling is not allowed for the reason specified.
  • The ScalingActive condition indicates whether the HPA is enabled (for example, the replica count of the target is not zero) and is able to calculate desired metrics.

    • A True condition indicates metrics is working properly.
    • A False condition generally indicates a problem with fetching metrics.
  • The ScalingLimited condition indicates that the desired scale was capped by the maximum or minimum of the horizontal pod autoscaler.

    • A True condition indicates that you need to raise or lower the minimum or maximum replica count in order to scale.
    • A False condition indicates that the requested scaling is allowed.

      $ oc describe hpa cm-test

      Example output

      Name:                           cm-test
      Namespace:                      prom
      Labels:                         <none>
      Annotations:                    <none>
      CreationTimestamp:              Fri, 16 Jun 2017 18:09:22 +0000
      Reference:                      ReplicationController/cm-test
      Metrics:                        ( current / target )
        "http_requests" on pods:      66m / 500m
      Min replicas:                   1
      Max replicas:                   4
      ReplicationController pods:     1 current / 1 desired
      Conditions: 1
        Type              Status    Reason              Message
        ----              ------    ------              -------
        AbleToScale       True      ReadyForNewScale    the last scale time was sufficiently old as to warrant a new scale
        ScalingActive     True      ValidMetricFound    the HPA was able to successfully calculate a replica count from pods metric http_request
        ScalingLimited    False     DesiredWithinRange  the desired replica count is within the acceptable range
      Events:

      1
      The horizontal pod autoscaler status messages.

The following is an example of a pod that is unable to scale:

Example output

Conditions:
  Type         Status  Reason          Message
  ----         ------  ------          -------
  AbleToScale  False   FailedGetScale  the HPA controller was unable to get the target's current scale: no matches for kind "ReplicationController" in group "apps"
Events:
  Type     Reason          Age               From                       Message
  ----     ------          ----              ----                       -------
  Warning  FailedGetScale  6s (x3 over 36s)  horizontal-pod-autoscaler  no matches for kind "ReplicationController" in group "apps"

The following is an example of a pod that could not obtain the needed metrics for scaling:

Example output

Conditions:
  Type                  Status    Reason                    Message
  ----                  ------    ------                    -------
  AbleToScale           True     SucceededGetScale          the HPA controller was able to get the target's current scale
  ScalingActive         False    FailedGetResourceMetric    the HPA was unable to compute the replica count: failed to get cpu utilization: unable to get metrics for resource cpu: no metrics returned from resource metrics API

The following is an example of a pod where the requested autoscaling was less than the required minimums:

Example output

Conditions:
  Type              Status    Reason              Message
  ----              ------    ------              -------
  AbleToScale       True      ReadyForNewScale    the last scale time was sufficiently old as to warrant a new scale
  ScalingActive     True      ValidMetricFound    the HPA was able to successfully calculate a replica count from pods metric http_request
  ScalingLimited    False     DesiredWithinRange  the desired replica count is within the acceptable range

2.4.8.1. Viewing horizontal pod autoscaler status conditions by using the CLI

You can view the status conditions set on a pod by the horizontal pod autoscaler (HPA).

Note

The horizontal pod autoscaler status conditions are available with the v2 version of the autoscaling API.

Prerequisites

To use horizontal pod autoscalers, your cluster administrator must have properly configured cluster metrics. You can use the oc describe PodMetrics <pod-name> command to determine if metrics are configured. If metrics are configured, the output appears similar to the following, with Cpu and Memory displayed under Usage.

$ oc describe PodMetrics openshift-kube-scheduler-ip-10-0-135-131.ec2.internal

Example output

Name:         openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Namespace:    openshift-kube-scheduler
Labels:       <none>
Annotations:  <none>
API Version:  metrics.k8s.io/v1beta1
Containers:
  Name:  wait-for-host-port
  Usage:
    Memory:  0
  Name:      scheduler
  Usage:
    Cpu:     8m
    Memory:  45440Ki
Kind:        PodMetrics
Metadata:
  Creation Timestamp:  2019-05-23T18:47:56Z
  Self Link:           /apis/metrics.k8s.io/v1beta1/namespaces/openshift-kube-scheduler/pods/openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
Timestamp:             2019-05-23T18:47:56Z
Window:                1m0s
Events:                <none>

Procedure

To view the status conditions on a pod, use the following command with the name of the pod:

$ oc describe hpa <pod-name>

For example:

$ oc describe hpa cm-test

The conditions appear in the Conditions field in the output.

Example output

Name:                           cm-test
Namespace:                      prom
Labels:                         <none>
Annotations:                    <none>
CreationTimestamp:              Fri, 16 Jun 2017 18:09:22 +0000
Reference:                      ReplicationController/cm-test
Metrics:                        ( current / target )
  "http_requests" on pods:      66m / 500m
Min replicas:                   1
Max replicas:                   4
ReplicationController pods:     1 current / 1 desired
Conditions: 1
  Type              Status    Reason              Message
  ----              ------    ------              -------
  AbleToScale       True      ReadyForNewScale    the last scale time was sufficiently old as to warrant a new scale
  ScalingActive     True      ValidMetricFound    the HPA was able to successfully calculate a replica count from pods metric http_request
  ScalingLimited    False     DesiredWithinRange  the desired replica count is within the acceptable range

2.4.9. Additional resources

2.5. Automatically adjust pod resource levels with the vertical pod autoscaler

The OpenShift Container Platform Vertical Pod Autoscaler Operator (VPA) automatically reviews the historic and current CPU and memory resources for containers in pods and can update the resource limits and requests based on the usage values it learns. The VPA uses individual custom resources (CR) to update all of the pods associated with a workload object, such as a Deployment, DeploymentConfig, StatefulSet, Job, DaemonSet, ReplicaSet, or ReplicationController, in a project.

The VPA helps you to understand the optimal CPU and memory usage for your pods and can automatically maintain pod resources through the pod lifecycle.

2.5.1. About the Vertical Pod Autoscaler Operator

The Vertical Pod Autoscaler Operator (VPA) is implemented as an API resource and a custom resource (CR). The CR determines the actions the Vertical Pod Autoscaler Operator should take with the pods associated with a specific workload object, such as a daemon set, replication controller, and so forth, in a project.

You can use the default recommender or use your own alternative recommender to autoscale based on your own algorithms.

The default recommender automatically computes historic and current CPU and memory usage for the containers in those pods and uses this data to determine optimized resource limits and requests to ensure that these pods are operating efficiently at all times. For example, the default recommender suggests reduced resources for pods that are requesting more resources than they are using and increased resources for pods that are not requesting enough.

The VPA then automatically deletes any pods that are out of alignment with these recommendations one at a time, so that your applications can continue to serve requests with no downtime. The workload objects then re-deploy the pods with the original resource limits and requests. The VPA uses a mutating admission webhook to update the pods with optimized resource limits and requests before the pods are admitted to a node. If you do not want the VPA to delete pods, you can view the VPA resource limits and requests and manually update the pods as needed.

Note

By default, workload objects must specify a minimum of two replicas in order for the VPA to automatically delete their pods. Workload objects that specify fewer replicas than this minimum are not deleted. If you manually delete these pods, when the workload object redeploys the pods, the VPA does update the new pods with its recommendations. You can change this minimum by modifying the VerticalPodAutoscalerController object as shown shown in Changing the VPA minimum value.

For example, if you have a pod that uses 50% of the CPU but only requests 10%, the VPA determines that the pod is consuming more CPU than requested and deletes the pod. The workload object, such as replica set, restarts the pods and the VPA updates the new pod with its recommended resources.

For developers, you can use the VPA to help ensure your pods stay up during periods of high demand by scheduling pods onto nodes that have appropriate resources for each pod.

Administrators can use the VPA to better utilize cluster resources, such as preventing pods from reserving more CPU resources than needed. The VPA monitors the resources that workloads are actually using and adjusts the resource requirements so capacity is available to other workloads. The VPA also maintains the ratios between limits and requests that are specified in initial container configuration.

Note

If you stop running the VPA or delete a specific VPA CR in your cluster, the resource requests for the pods already modified by the VPA do not change. Any new pods get the resources defined in the workload object, not the previous recommendations made by the VPA.

2.5.2. Installing the Vertical Pod Autoscaler Operator

You can use the OpenShift Container Platform web console to install the Vertical Pod Autoscaler Operator (VPA).

Procedure

  1. In the OpenShift Container Platform web console, click OperatorsOperatorHub.
  2. Choose VerticalPodAutoscaler from the list of available Operators, and click Install.
  3. On the Install Operator page, ensure that the Operator recommended namespace option is selected. This installs the Operator in the mandatory openshift-vertical-pod-autoscaler namespace, which is automatically created if it does not exist.
  4. Click Install.

Verifiction

  1. Verify the installation by listing the VPA Operator components:

    1. Navigate to WorkloadsPods.
    2. Select the openshift-vertical-pod-autoscaler project from the drop-down menu and verify that there are four pods running.
    3. Navigate to WorkloadsDeployments to verify that there are four deployments running.
  2. Optional: Verify the installation in the OpenShift Container Platform CLI using the following command:

    $ oc get all -n openshift-vertical-pod-autoscaler

    The output shows four pods and four deplyoments:

    Example output

    NAME                                                    READY   STATUS    RESTARTS   AGE
    pod/vertical-pod-autoscaler-operator-85b4569c47-2gmhc   1/1     Running   0          3m13s
    pod/vpa-admission-plugin-default-67644fc87f-xq7k9       1/1     Running   0          2m56s
    pod/vpa-recommender-default-7c54764b59-8gckt            1/1     Running   0          2m56s
    pod/vpa-updater-default-7f6cc87858-47vw9                1/1     Running   0          2m56s
    
    NAME                  TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)   AGE
    service/vpa-webhook   ClusterIP   172.30.53.206   <none>        443/TCP   2m56s
    
    NAME                                               READY   UP-TO-DATE   AVAILABLE   AGE
    deployment.apps/vertical-pod-autoscaler-operator   1/1     1            1           3m13s
    deployment.apps/vpa-admission-plugin-default       1/1     1            1           2m56s
    deployment.apps/vpa-recommender-default            1/1     1            1           2m56s
    deployment.apps/vpa-updater-default                1/1     1            1           2m56s
    
    NAME                                                          DESIRED   CURRENT   READY   AGE
    replicaset.apps/vertical-pod-autoscaler-operator-85b4569c47   1         1         1       3m13s
    replicaset.apps/vpa-admission-plugin-default-67644fc87f       1         1         1       2m56s
    replicaset.apps/vpa-recommender-default-7c54764b59            1         1         1       2m56s
    replicaset.apps/vpa-updater-default-7f6cc87858                1         1         1       2m56s

2.5.3. About Using the Vertical Pod Autoscaler Operator

To use the Vertical Pod Autoscaler Operator (VPA), you create a VPA custom resource (CR) for a workload object in your cluster. The VPA learns and applies the optimal CPU and memory resources for the pods associated with that workload object. You can use a VPA with a deployment, stateful set, job, daemon set, replica set, or replication controller workload object. The VPA CR must be in the same project as the pods you want to monitor.

You use the VPA CR to associate a workload object and specify which mode the VPA operates in:

  • The Auto and Recreate modes automatically apply the VPA CPU and memory recommendations throughout the pod lifetime. The VPA deletes any pods in the project that are out of alignment with its recommendations. When redeployed by the workload object, the VPA updates the new pods with its recommendations.
  • The Initial mode automatically applies VPA recommendations only at pod creation.
  • The Off mode only provides recommended resource limits and requests, allowing you to manually apply the recommendations. The off mode does not update pods.

You can also use the CR to opt-out certain containers from VPA evaluation and updates.

For example, a pod has the following limits and requests:

resources:
  limits:
    cpu: 1
    memory: 500Mi
  requests:
    cpu: 500m
    memory: 100Mi

After creating a VPA that is set to auto, the VPA learns the resource usage and deletes the pod. When redeployed, the pod uses the new resource limits and requests:

resources:
  limits:
    cpu: 50m
    memory: 1250Mi
  requests:
    cpu: 25m
    memory: 262144k

You can view the VPA recommendations using the following command:

$ oc get vpa <vpa-name> --output yaml

After a few minutes, the output shows the recommendations for CPU and memory requests, similar to the following:

Example output

...
status:
...
  recommendation:
    containerRecommendations:
    - containerName: frontend
      lowerBound:
        cpu: 25m
        memory: 262144k
      target:
        cpu: 25m
        memory: 262144k
      uncappedTarget:
        cpu: 25m
        memory: 262144k
      upperBound:
        cpu: 262m
        memory: "274357142"
    - containerName: backend
      lowerBound:
        cpu: 12m
        memory: 131072k
      target:
        cpu: 12m
        memory: 131072k
      uncappedTarget:
        cpu: 12m
        memory: 131072k
      upperBound:
        cpu: 476m
        memory: "498558823"
...

The output shows the recommended resources, target, the minimum recommended resources, lowerBound, the highest recommended resources, upperBound, and the most recent resource recommendations, uncappedTarget.

The VPA uses the lowerBound and upperBound values to determine if a pod needs to be updated. If a pod has resource requests below the lowerBound values or above the upperBound values, the VPA terminates and recreates the pod with the target values.

2.5.3.1. Changing the VPA minimum value

By default, workload objects must specify a minimum of two replicas in order for the VPA to automatically delete and update their pods. As a result, workload objects that specify fewer than two replicas are not automatically acted upon by the VPA. The VPA does update new pods from these workload objects if the pods are restarted by some process external to the VPA. You can change this cluster-wide minimum value by modifying the minReplicas parameter in the VerticalPodAutoscalerController custom resource (CR).

For example, if you set minReplicas to 3, the VPA does not delete and update pods for workload objects that specify fewer than three replicas.

Note

If you set minReplicas to 1, the VPA can delete the only pod for a workload object that specifies only one replica. You should use this setting with one-replica objects only if your workload can tolerate downtime whenever the VPA deletes a pod to adjust its resources. To avoid unwanted downtime with one-replica objects, configure the VPA CRs with the podUpdatePolicy set to Initial, which automatically updates the pod only when it is restarted by some process external to the VPA, or Off, which allows you to update the pod manually at an appropriate time for your application.

Example VerticalPodAutoscalerController object

apiVersion: autoscaling.openshift.io/v1
kind: VerticalPodAutoscalerController
metadata:
  creationTimestamp: "2021-04-21T19:29:49Z"
  generation: 2
  name: default
  namespace: openshift-vertical-pod-autoscaler
  resourceVersion: "142172"
  uid: 180e17e9-03cc-427f-9955-3b4d7aeb2d59
spec:
  minReplicas: 3 1
  podMinCPUMillicores: 25
  podMinMemoryMb: 250
  recommendationOnly: false
  safetyMarginFraction: 0.15

1 1
Specify the minimum number of replicas in a workload object for the VPA to act on. Any objects with replicas fewer than the minimum are not automatically deleted by the VPA.
2.5.3.2. Automatically applying VPA recommendations

To use the VPA to automatically update pods, create a VPA CR for a specific workload object with updateMode set to Auto or Recreate.

When the pods are created for the workload object, the VPA constantly monitors the containers to analyze their CPU and memory needs. The VPA deletes any pods that do not meet the VPA recommendations for CPU and memory. When redeployed, the pods use the new resource limits and requests based on the VPA recommendations, honoring any pod disruption budget set for your applications. The recommendations are added to the status field of the VPA CR for reference.

Note

By default, workload objects must specify a minimum of two replicas in order for the VPA to automatically delete their pods. Workload objects that specify fewer replicas than this minimum are not deleted. If you manually delete these pods, when the workload object redeploys the pods, the VPA does update the new pods with its recommendations. You can change this minimum by modifying the VerticalPodAutoscalerController object as shown shown in Changing the VPA minimum value.

Example VPA CR for the Auto mode

apiVersion: autoscaling.k8s.io/v1
kind: VerticalPodAutoscaler
metadata:
  name: vpa-recommender
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind:       Deployment 1
    name:       frontend 2
  updatePolicy:
    updateMode: "Auto" 3

1
The type of workload object you want this VPA CR to manage.
2
The name of the workload object you want this VPA CR to manage.
3
Set the mode to Auto or Recreate:
  • Auto. The VPA assigns resource requests on pod creation and updates the existing pods by terminating them when the requested resources differ significantly from the new recommendation.
  • Recreate. The VPA assigns resource requests on pod creation and updates the existing pods by terminating them when the requested resources differ significantly from the new recommendation. This mode should be used rarely, only if you need to ensure that the pods are restarted whenever the resource request changes.
Note

Before a VPA can determine recommendations for resources and apply the recommended resources to new pods, operating pods must exist and be running in the project.

If a workload’s resource usage, such as CPU and memory, is consistent, the VPA can determine recommendations for resources in a few minutes. If a workload’s resource usage is inconsistent, the VPA must collect metrics at various resource usage intervals for the VPA to make an accurate recommendation.

2.5.3.3. Automatically applying VPA recommendations on pod creation

To use the VPA to apply the recommended resources only when a pod is first deployed, create a VPA CR for a specific workload object with updateMode set to Initial.

Then, manually delete any pods associated with the workload object that you want to use the VPA recommendations. In the Initial mode, the VPA does not delete pods and does not update the pods as it learns new resource recommendations.

Example VPA CR for the Initial mode

apiVersion: autoscaling.k8s.io/v1
kind: VerticalPodAutoscaler
metadata:
  name: vpa-recommender
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind:       Deployment 1
    name:       frontend 2
  updatePolicy:
    updateMode: "Initial" 3

1
The type of workload object you want this VPA CR to manage.
2
The name of the workload object you want this VPA CR to manage.
3
Set the mode to Initial. The VPA assigns resources when pods are created and does not change the resources during the lifetime of the pod.
Note

Before a VPA can determine recommended resources and apply the recommendations to new pods, operating pods must exist and be running in the project.

To obtain the most accurate recommendations from the VPA, wait at least 8 days for the pods to run and for the VPA to stabilize.

2.5.3.4. Manually applying VPA recommendations

To use the VPA to only determine the recommended CPU and memory values, create a VPA CR for a specific workload object with updateMode set to off.

When the pods are created for that workload object, the VPA analyzes the CPU and memory needs of the containers and records those recommendations in the status field of the VPA CR. The VPA does not update the pods as it determines new resource recommendations.

Example VPA CR for the Off mode

apiVersion: autoscaling.k8s.io/v1
kind: VerticalPodAutoscaler
metadata:
  name: vpa-recommender
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind:       Deployment 1
    name:       frontend 2
  updatePolicy:
    updateMode: "Off" 3

1
The type of workload object you want this VPA CR to manage.
2
The name of the workload object you want this VPA CR to manage.
3
Set the mode to Off.

You can view the recommendations using the following command.

$ oc get vpa <vpa-name> --output yaml

With the recommendations, you can edit the workload object to add CPU and memory requests, then delete and redeploy the pods using the recommended resources.

Note

Before a VPA can determine recommended resources and apply the recommendations to new pods, operating pods must exist and be running in the project.

To obtain the most accurate recommendations from the VPA, wait at least 8 days for the pods to run and for the VPA to stabilize.

2.5.3.5. Exempting containers from applying VPA recommendations

If your workload object has multiple containers and you do not want the VPA to evaluate and act on all of the containers, create a VPA CR for a specific workload object and add a resourcePolicy to opt-out specific containers.

When the VPA updates the pods with recommended resources, any containers with a resourcePolicy are not updated and the VPA does not present recommendations for those containers in the pod.

apiVersion: autoscaling.k8s.io/v1
kind: VerticalPodAutoscaler
metadata:
  name: vpa-recommender
spec:
  targetRef:
    apiVersion: "apps/v1"
    kind:       Deployment 1
    name:       frontend 2
  updatePolicy:
    updateMode: "Auto" 3
  resourcePolicy: 4
    containerPolicies:
    - containerName: my-opt-sidecar
      mode: "Off"
1
The type of workload object you want this VPA CR to manage.
2
The name of the workload object you want this VPA CR to manage.
3
Set the mode to Auto, Recreate, or Off. The Recreate mode should be used rarely, only if you need to ensure that the pods are restarted whenever the resource request changes.
4
Specify the containers you want to opt-out and set mode to Off.

For example, a pod has two containers, the same resource requests and limits:

# ...
spec:
  containers:
  - name: frontend
    resources:
      limits:
        cpu: 1
        memory: 500Mi
      requests:
        cpu: 500m
        memory: 100Mi
  - name: backend
    resources:
      limits:
        cpu: "1"
        memory: 500Mi
      requests:
        cpu: 500m
        memory: 100Mi
# ...

After launching a VPA CR with the backend container set to opt-out, the VPA terminates and recreates the pod with the recommended resources applied only to the frontend container:

...
spec:
  containers:
    name: frontend
    resources:
      limits:
        cpu: 50m
        memory: 1250Mi
      requests:
        cpu: 25m
        memory: 262144k
...
    name: backend
    resources:
      limits:
        cpu: "1"
        memory: 500Mi
      requests:
        cpu: 500m
        memory: 100Mi
...
2.5.3.6. Using an alternative recommender

You can use your own recommender to autoscale based on your own algorithms. If you do not specify an alternative recommender, OpenShift Container Platform uses the default recommender, which suggests CPU and memory requests based on historical usage. Because there is no universal recommendation policy that applies to all types of workloads, you might want to create and deploy different recommenders for specific workloads.

For example, the default recommender might not accurately predict future resource usage when containers exhibit certain resource behaviors, such as cyclical patterns that alternate between usage spikes and idling as used by monitoring applications, or recurring and repeating patterns used with deep learning applications. Using the default recommender with these usage behaviors might result in significant over-provisioning and Out of Memory (OOM) kills for your applications.

Note

Instructions for how to create a recommender are beyond the scope of this documentation,

Procedure

To use an alternative recommender for your pods:

  1. Create a service account for the alternative recommender and bind that service account to the required cluster role:

    apiVersion: v1 1
    kind: ServiceAccount
    metadata:
      name: alt-vpa-recommender-sa
      namespace: <namespace_name>
    ---
    apiVersion: rbac.authorization.k8s.io/v1 2
    kind: ClusterRoleBinding
    metadata:
      name: system:example-metrics-reader
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: system:metrics-reader
    subjects:
    - kind: ServiceAccount
      name: alt-vpa-recommender-sa
      namespace: <namespace_name>
    ---
    apiVersion: rbac.authorization.k8s.io/v1 3
    kind: ClusterRoleBinding
    metadata:
      name: system:example-vpa-actor
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: system:vpa-actor
    subjects:
    - kind: ServiceAccount
      name: alt-vpa-recommender-sa
      namespace: <namespace_name>
    ---
    apiVersion: rbac.authorization.k8s.io/v1 4
    kind: ClusterRoleBinding
    metadata:
      name: system:example-vpa-target-reader-binding
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: system:vpa-target-reader
    subjects:
    - kind: ServiceAccount
      name: alt-vpa-recommender-sa
      namespace: <namespace_name>
    1
    Creates a service accocunt for the recommender in the namespace where the recommender is deployed.
    2
    Binds the recommender service account to the metrics-reader role. Specify the namespace where the recommender is to be deployed.
    3
    Binds the recommender service account to the vpa-actor role. Specify the namespace where the recommender is to be deployed.
    4
    Binds the recommender service account to the vpa-target-reader role. Specify the namespace where the recommender is to be deployed.
  2. To add the alternative recommender to the cluster, create a Deployment object similar to the following:

    apiVersion: apps/v1
    kind: Deployment
    metadata:
      name: alt-vpa-recommender
      namespace: <namespace_name>
    spec:
      replicas: 1
      selector:
        matchLabels:
          app: alt-vpa-recommender
      template:
        metadata:
          labels:
            app: alt-vpa-recommender
        spec:
          containers: 1
          - name: recommender
            image: quay.io/example/alt-recommender:latest 2
            imagePullPolicy: Always
            resources:
              limits:
                cpu: 200m
                memory: 1000Mi
              requests:
                cpu: 50m
                memory: 500Mi
            ports:
            - name: prometheus
              containerPort: 8942
            securityContext:
              allowPrivilegeEscalation: false
              capabilities:
                drop:
                  - ALL
              seccompProfile:
                type: RuntimeDefault
          serviceAccountName: alt-vpa-recommender-sa 3
          securityContext:
            runAsNonRoot: true
    1
    Creates a container for your alternative recommender.
    2
    Specifies your recommender image.
    3
    Associates the service account that you created for the recommender.

    A new pod is created for the alternative recommender in the same namespace.

    $ oc get pods

    Example output

    NAME                                        READY   STATUS    RESTARTS   AGE
    frontend-845d5478d-558zf                    1/1     Running   0          4m25s
    frontend-845d5478d-7z9gx                    1/1     Running   0          4m25s
    frontend-845d5478d-b7l4j                    1/1     Running   0          4m25s
    vpa-alt-recommender-55878867f9-6tp5v        1/1     Running   0          9s

  3. Configure a VPA CR that includes the name of the alternative recommender Deployment object.

    Example VPA CR to include the alternative recommender

    apiVersion: autoscaling.k8s.io/v1
    kind: VerticalPodAutoscaler
    metadata:
      name: vpa-recommender
      namespace: <namespace_name>
    spec:
      recommenders:
        - name: alt-vpa-recommender 1
      targetRef:
        apiVersion: "apps/v1"
        kind:       Deployment 2
        name:       frontend

    1
    Specifies the name of the alternative recommender deployment.
    2
    Specifies the name of an existing workload object you want this VPA to manage.

2.5.4. Using the Vertical Pod Autoscaler Operator

You can use the Vertical Pod Autoscaler Operator (VPA) by creating a VPA custom resource (CR). The CR indicates which pods it should analyze and determines the actions the VPA should take with those pods.

Prerequisites

  • The workload object that you want to autoscale must exist.
  • If you want to use an alternative recommender, a deployment including that recommender must exist.

Procedure

To create a VPA CR for a specific workload object:

  1. Change to the project where the workload object you want to scale is located.

    1. Create a VPA CR YAML file:

      apiVersion: autoscaling.k8s.io/v1
      kind: VerticalPodAutoscaler
      metadata:
        name: vpa-recommender
      spec:
        targetRef:
          apiVersion: "apps/v1"
          kind:       Deployment 1
          name:       frontend 2
        updatePolicy:
          updateMode: "Auto" 3
        resourcePolicy: 4
          containerPolicies:
          - containerName: my-opt-sidecar
            mode: "Off"
        recommenders: 5
          - name: my-recommender
      1
      Specify the type of workload object you want this VPA to manage: Deployment, StatefulSet, Job, DaemonSet, ReplicaSet, or ReplicationController.
      2
      Specify the name of an existing workload object you want this VPA to manage.
      3
      Specify the VPA mode:
      • auto to automatically apply the recommended resources on pods associated with the controller. The VPA terminates existing pods and creates new pods with the recommended resource limits and requests.
      • recreate to automatically apply the recommended resources on pods associated with the workload object. The VPA terminates existing pods and creates new pods with the recommended resource limits and requests. The recreate mode should be used rarely, only if you need to ensure that the pods are restarted whenever the resource request changes.
      • initial to automatically apply the recommended resources when pods associated with the workload object are created. The VPA does not update the pods as it learns new resource recommendations.
      • off to only generate resource recommendations for the pods associated with the workload object. The VPA does not update the pods as it learns new resource recommendations and does not apply the recommendations to new pods.
      4
      Optional. Specify the containers you want to opt-out and set the mode to Off.
      5
      Optional. Specify an alternative recommender.
    2. Create the VPA CR:

      $ oc create -f <file-name>.yaml

      After a few moments, the VPA learns the resource usage of the containers in the pods associated with the workload object.

      You can view the VPA recommendations using the following command:

      $ oc get vpa <vpa-name> --output yaml

      The output shows the recommendations for CPU and memory requests, similar to the following:

      Example output

      ...
      status:
      
      ...
      
        recommendation:
          containerRecommendations:
          - containerName: frontend
            lowerBound: 1
              cpu: 25m
              memory: 262144k
            target: 2
              cpu: 25m
              memory: 262144k
            uncappedTarget: 3
              cpu: 25m
              memory: 262144k
            upperBound: 4
              cpu: 262m
              memory: "274357142"
          - containerName: backend
            lowerBound:
              cpu: 12m
              memory: 131072k
            target:
              cpu: 12m
              memory: 131072k
            uncappedTarget:
              cpu: 12m
              memory: 131072k
            upperBound:
              cpu: 476m
              memory: "498558823"
      
      ...

      1
      lowerBound is the minimum recommended resource levels.
      2
      target is the recommended resource levels.
      3
      upperBound is the highest recommended resource levels.
      4
      uncappedTarget is the most recent resource recommendations.

2.5.5. Uninstalling the Vertical Pod Autoscaler Operator

You can remove the Vertical Pod Autoscaler Operator (VPA) from your OpenShift Container Platform cluster. After uninstalling, the resource requests for the pods already modified by an existing VPA CR do not change. Any new pods get the resources defined in the workload object, not the previous recommendations made by the Vertical Pod Autoscaler Operator.

Note

You can remove a specific VPA CR by using the oc delete vpa <vpa-name> command. The same actions apply for resource requests as uninstalling the vertical pod autoscaler.

After removing the VPA Operator, it is recommended that you remove the other components associated with the Operator to avoid potential issues.

Prerequisites

  • The Vertical Pod Autoscaler Operator must be installed.

Procedure

  1. In the OpenShift Container Platform web console, click OperatorsInstalled Operators.
  2. Switch to the openshift-vertical-pod-autoscaler project.
  3. For the VerticalPodAutoscaler Operator, click the Options menu kebab and select Uninstall Operator.
  4. Optional: To remove all operands associated with the Operator, in the dialog box, select Delete all operand instances for this operator checkbox.
  5. Click Uninstall.
  6. Optional: Use the OpenShift CLI to remove the VPA components:

    1. Delete the VPA namespace:

      $ oc delete namespace openshift-vertical-pod-autoscaler
    2. Delete the VPA custom resource definition (CRD) objects:

      $ oc delete crd verticalpodautoscalercheckpoints.autoscaling.k8s.io
      $ oc delete crd verticalpodautoscalercontrollers.autoscaling.openshift.io
      $ oc delete crd verticalpodautoscalers.autoscaling.k8s.io

      Deleting the CRDs removes the associated roles, cluster roles, and role bindings.

      Note

      This action removes from the cluster all user-created VPA CRs. If you re-install the VPA, you must create these objects again.

    3. Delete the MutatingWebhookConfiguration object by running the following command:

      $ oc delete MutatingWebhookConfiguration vpa-webhook-config
    4. Delete the VPA Operator:

      $ oc delete operator/vertical-pod-autoscaler.openshift-vertical-pod-autoscaler

2.6. Providing sensitive data to pods

Some applications need sensitive information, such as passwords and user names, that you do not want developers to have.

As an administrator, you can use Secret objects to provide this information without exposing that information in clear text.

2.6.1. Understanding secrets

The Secret object type provides a mechanism to hold sensitive information such as passwords, OpenShift Container Platform client configuration files, private source repository credentials, and so on. Secrets decouple sensitive content from the pods. You can mount secrets into containers using a volume plugin or the system can use secrets to perform actions on behalf of a pod.

Key properties include:

  • Secret data can be referenced independently from its definition.
  • Secret data volumes are backed by temporary file-storage facilities (tmpfs) and never come to rest on a node.
  • Secret data can be shared within a namespace.

YAML Secret object definition

apiVersion: v1
kind: Secret
metadata:
  name: test-secret
  namespace: my-namespace
type: Opaque 1
data: 2
  username: <username> 3
  password: <password>
stringData: 4
  hostname: myapp.mydomain.com 5

1
Indicates the structure of the secret’s key names and values.
2
The allowable format for the keys in the data field must meet the guidelines in the DNS_SUBDOMAIN value in the Kubernetes identifiers glossary.
3
The value associated with keys in the data map must be base64 encoded.
4
Entries in the stringData map are converted to base64 and the entry will then be moved to the data map automatically. This field is write-only; the value will only be returned via the data field.
5
The value associated with keys in the stringData map is made up of plain text strings.

You must create a secret before creating the pods that depend on that secret.

When creating secrets:

  • Create a secret object with secret data.
  • Update the pod’s service account to allow the reference to the secret.
  • Create a pod, which consumes the secret as an environment variable or as a file (using a secret volume).
2.6.1.1. Types of secrets

The value in the type field indicates the structure of the secret’s key names and values. The type can be used to enforce the presence of user names and keys in the secret object. If you do not want validation, use the opaque type, which is the default.

Specify one of the following types to trigger minimal server-side validation to ensure the presence of specific key names in the secret data:

  • kubernetes.io/basic-auth: Use with Basic authentication
  • kubernetes.io/dockercfg: Use as an image pull secret
  • kubernetes.io/dockerconfigjson: Use as an image pull secret
  • kubernetes.io/service-account-token: Use to obtain a legacy service account API token
  • kubernetes.io/ssh-auth: Use with SSH key authentication
  • kubernetes.io/tls: Use with TLS certificate authorities

Specify type: Opaque if you do not want validation, which means the secret does not claim to conform to any convention for key names or values. An opaque secret, allows for unstructured key:value pairs that can contain arbitrary values.

Note

You can specify other arbitrary types, such as example.com/my-secret-type. These types are not enforced server-side, but indicate that the creator of the secret intended to conform to the key/value requirements of that type.

For examples of creating different types of secrets, see Understanding how to create secrets.

2.6.1.2. Secret data keys

Secret keys must be in a DNS subdomain.

2.6.1.3. About automatically generated service account token secrets

When a service account is created, a service account token secret is automatically generated for it. This service account token secret, along with an automatically generated docker configuration secret, is used to authenticate to the internal OpenShift Container Platform registry. Do not rely on these automatically generated secrets for your own use; they might be removed in a future OpenShift Container Platform release.

Note

Prior to OpenShift Container Platform 4.11, a second service account token secret was generated when a service account was created. This service account token secret was used to access the Kubernetes API.

Starting with OpenShift Container Platform 4.11, this second service account token secret is no longer created. This is because the LegacyServiceAccountTokenNoAutoGeneration upstream Kubernetes feature gate was enabled, which stops the automatic generation of secret-based service account tokens to access the Kubernetes API.

After upgrading to 4.12, any existing service account token secrets are not deleted and continue to function.

Workloads are automatically injected with a projected volume to obtain a bound service account token. If your workload needs an additional service account token, add an additional projected volume in your workload manifest. Bound service account tokens are more secure than service account token secrets for the following reasons:

  • Bound service account tokens have a bounded lifetime.
  • Bound service account tokens contain audiences.
  • Bound service account tokens can be bound to pods or secrets and the bound tokens are invalidated when the bound object is removed.

For more information, see Configuring bound service account tokens using volume projection.

You can also manually create a service account token secret to obtain a token, if the security exposure of a non-expiring token in a readable API object is acceptable to you. For more information, see Creating a service account token secret.

Additional resources

2.6.2. Understanding how to create secrets

As an administrator you must create a secret before developers can create the pods that depend on that secret.

When creating secrets:

  1. Create a secret object that contains the data you want to keep secret. The specific data required for each secret type is descibed in the following sections.

    Example YAML object that creates an opaque secret

    apiVersion: v1
    kind: Secret
    metadata:
      name: test-secret
    type: Opaque 1
    data: 2
      username: <username>
      password: <password>
    stringData: 3
      hostname: myapp.mydomain.com
      secret.properties: |
        property1=valueA
        property2=valueB

    1
    Specifies the type of secret.
    2
    Specifies encoded string and data.
    3
    Specifies decoded string and data.

    Use either the data or stringdata fields, not both.

  2. Update the pod’s service account to reference the secret:

    YAML of a service account that uses a secret

    apiVersion: v1
    kind: ServiceAccount
     ...
    secrets:
    - name: test-secret

  3. Create a pod, which consumes the secret as an environment variable or as a file (using a secret volume):

    YAML of a pod populating files in a volume with secret data

    apiVersion: v1
    kind: Pod
    metadata:
      name: secret-example-pod
    spec:
      containers:
        - name: secret-test-container
          image: busybox
          command: [ "/bin/sh", "-c", "cat /etc/secret-volume/*" ]
          volumeMounts: 1
              - name: secret-volume
                mountPath: /etc/secret-volume 2
                readOnly: true 3
      volumes:
        - name: secret-volume
          secret:
            secretName: test-secret 4
      restartPolicy: Never

    1
    Add a volumeMounts field to each container that needs the secret.
    2
    Specifies an unused directory name where you would like the secret to appear. Each key in the secret data map becomes the filename under mountPath.
    3
    Set to true. If true, this instructs the driver to provide a read-only volume.
    4
    Specifies the name of the secret.

    YAML of a pod populating environment variables with secret data

    apiVersion: v1
    kind: Pod
    metadata:
      name: secret-example-pod
    spec:
      containers:
        - name: secret-test-container
          image: busybox
          command: [ "/bin/sh", "-c", "export" ]
          env:
            - name: TEST_SECRET_USERNAME_ENV_VAR
              valueFrom:
                secretKeyRef: 1
                  name: test-secret
                  key: username
      restartPolicy: Never

    1
    Specifies the environment variable that consumes the secret key.

    YAML of a build config populating environment variables with secret data

    apiVersion: build.openshift.io/v1
    kind: BuildConfig
    metadata:
      name: secret-example-bc
    spec:
      strategy:
        sourceStrategy:
          env:
          - name: TEST_SECRET_USERNAME_ENV_VAR
            valueFrom:
              secretKeyRef: 1
                name: test-secret
                key: username
          from:
            kind: ImageStreamTag
            namespace: openshift
            name: 'cli:latest'

    1
    Specifies the environment variable that consumes the secret key.
2.6.2.1. Secret creation restrictions

To use a secret, a pod needs to reference the secret. A secret can be used with a pod in three ways:

  • To populate environment variables for containers.
  • As files in a volume mounted on one or more of its containers.
  • By kubelet when pulling images for the pod.

Volume type secrets write data into the container as a file using the volume mechanism. Image pull secrets use service accounts for the automatic injection of the secret into all pods in a namespace.

When a template contains a secret definition, the only way for the template to use the provided secret is to ensure that the secret volume sources are validated and that the specified object reference actually points to a Secret object. Therefore, a secret needs to be created before any pods that depend on it. The most effective way to ensure this is to have it get injected automatically through the use of a service account.

Secret API objects reside in a namespace. They can only be referenced by pods in that same namespace.

Individual secrets are limited to 1MB in size. This is to discourage the creation of large secrets that could exhaust apiserver and kubelet memory. However, creation of a number of smaller secrets could also exhaust memory.

2.6.2.2. Creating an opaque secret

As an administrator, you can create an opaque secret, which allows you to store unstructured key:value pairs that can contain arbitrary values.

Procedure

  1. Create a Secret object in a YAML file on a control plane node.

    For example:

    apiVersion: v1
    kind: Secret
    metadata:
      name: mysecret
    type: Opaque 1
    data:
      username: <username>
      password: <password>
    1
    Specifies an opaque secret.
  2. Use the following command to create a Secret object:

    $ oc create -f <filename>.yaml
  3. To use the secret in a pod:

    1. Update the pod’s service account to reference the secret, as shown in the "Understanding how to create secrets" section.
    2. Create the pod, which consumes the secret as an environment variable or as a file (using a secret volume), as shown in the "Understanding how to create secrets" section.

Additional resources

2.6.2.3. Creating a service account token secret

As an administrator, you can create a service account token secret, which allows you to distribute a service account token to applications that must authenticate to the API.

Note

It is recommended to obtain bound service account tokens using the TokenRequest API instead of using service account token secrets. The tokens obtained from the TokenRequest API are more secure than the tokens stored in secrets, because they have a bounded lifetime and are not readable by other API clients.

You should create a service account token secret only if you cannot use the TokenRequest API and if the security exposure of a non-expiring token in a readable API object is acceptable to you.

See the Additional resources section that follows for information on creating bound service account tokens.

Procedure

  1. Create a Secret object in a YAML file on a control plane node:

    Example secret object:

    apiVersion: v1
    kind: Secret
    metadata:
      name: secret-sa-sample
      annotations:
        kubernetes.io/service-account.name: "sa-name" 1
    type: kubernetes.io/service-account-token 2

    1
    Specifies an existing service account name. If you are creating both the ServiceAccount and the Secret objects, create the ServiceAccount object first.
    2
    Specifies a service account token secret.
  2. Use the following command to create the Secret object:

    $ oc create -f <filename>.yaml
  3. To use the secret in a pod:

    1. Update the pod’s service account to reference the secret, as shown in the "Understanding how to create secrets" section.
    2. Create the pod, which consumes the secret as an environment variable or as a file (using a secret volume), as shown in the "Understanding how to create secrets" section.

Additional resources

2.6.2.4. Creating a basic authentication secret

As an administrator, you can create a basic authentication secret, which allows you to store the credentials needed for basic authentication. When using this secret type, the data parameter of the Secret object must contain the following keys encoded in the base64 format:

  • username: the user name for authentication
  • password: the password or token for authentication
Note

You can use the stringData parameter to use clear text content.

Procedure

  1. Create a Secret object in a YAML file on a control plane node:

    Example secret object

    apiVersion: v1
    kind: Secret
    metadata:
      name: secret-basic-auth
    type: kubernetes.io/basic-auth 1
    data:
    stringData: 2
      username: admin
      password: <password>

    1
    Specifies a basic authentication secret.
    2
    Specifies the basic authentication values to use.
  2. Use the following command to create the Secret object:

    $ oc create -f <filename>.yaml
  3. To use the secret in a pod:

    1. Update the pod’s service account to reference the secret, as shown in the "Understanding how to create secrets" section.
    2. Create the pod, which consumes the secret as an environment variable or as a file (using a secret volume), as shown in the "Understanding how to create secrets" section.

Additional resources

2.6.2.5. Creating an SSH authentication secret

As an administrator, you can create an SSH authentication secret, which allows you to store data used for SSH authentication. When using this secret type, the data parameter of the Secret object must contain the SSH credential to use.

Procedure

  1. Create a Secret object in a YAML file on a control plane node:

    Example secret object:

    apiVersion: v1
    kind: Secret
    metadata:
      name: secret-ssh-auth
    type: kubernetes.io/ssh-auth 1
    data:
      ssh-privatekey: | 2
              MIIEpQIBAAKCAQEAulqb/Y ...

    1
    Specifies an SSH authentication secret.
    2
    Specifies the SSH key/value pair as the SSH credentials to use.
  2. Use the following command to create the Secret object:

    $ oc create -f <filename>.yaml
  3. To use the secret in a pod:

    1. Update the pod’s service account to reference the secret, as shown in the "Understanding how to create secrets" section.
    2. Create the pod, which consumes the secret as an environment variable or as a file (using a secret volume), as shown in the "Understanding how to create secrets" section.
2.6.2.6. Creating a Docker configuration secret

As an administrator, you can create a Docker configuration secret, which allows you to store the credentials for accessing a container image registry.

  • kubernetes.io/dockercfg. Use this secret type to store your local Docker configuration file. The data parameter of the secret object must contain the contents of a .dockercfg file encoded in the base64 format.
  • kubernetes.io/dockerconfigjson. Use this secret type to store your local Docker configuration JSON file. The data parameter of the secret object must contain the contents of a .docker/config.json file encoded in the base64 format.

Procedure

  1. Create a Secret object in a YAML file on a control plane node.

    Example Docker configuration secret object

    apiVersion: v1
    kind: Secret
    metadata:
      name: secret-docker-cfg
      namespace: my-project
    type: kubernetes.io/dockerconfig 1
    data:
      .dockerconfig:bm5ubm5ubm5ubm5ubm5ubm5ubm5ubmdnZ2dnZ2dnZ2dnZ2dnZ2dnZ2cgYXV0aCBrZXlzCg== 2

    1
    Specifies that the secret is using a Docker configuration file.
    2
    The output of a base64-encoded Docker configuration file

    Example Docker configuration JSON secret object

    apiVersion: v1
    kind: Secret
    metadata:
      name: secret-docker-json
      namespace: my-project
    type: kubernetes.io/dockerconfig 1
    data:
      .dockerconfigjson:bm5ubm5ubm5ubm5ubm5ubm5ubm5ubmdnZ2dnZ2dnZ2dnZ2dnZ2dnZ2cgYXV0aCBrZXlzCg== 2

    1
    Specifies that the secret is using a Docker configuration JSONfile.
    2
    The output of a base64-encoded Docker configuration JSON file
  2. Use the following command to create the Secret object

    $ oc create -f <filename>.yaml
  3. To use the secret in a pod:

    1. Update the pod’s service account to reference the secret, as shown in the "Understanding how to create secrets" section.
    2. Create the pod, which consumes the secret as an environment variable or as a file (using a secret volume), as shown in the "Understanding how to create secrets" section.

Additional resources

2.6.2.7. Creating a secret using the web console

You can create secrets using the web console.

Procedure

  1. Navigate to WorkloadsSecrets.
  2. Click CreateFrom YAML.

    1. Edit the YAML manually to your specifications, or drag and drop a file into the YAML editor. For example:

      apiVersion: v1
      kind: Secret
      metadata:
        name: example
        namespace: <namespace>
      type: Opaque 1
      data:
        username: <base64 encoded username>
        password: <base64 encoded password>
      stringData: 2
        hostname: myapp.mydomain.com
      1
      This example specifies an opaque secret; however, you may see other secret types such as service account token secret, basic authentication secret, SSH authentication secret, or a secret that uses Docker configuration.
      2
      Entries in the stringData map are converted to base64 and the entry will then be moved to the data map automatically. This field is write-only; the value will only be returned via the data field.
  3. Click Create.
  4. Click Add Secret to workload.

    1. From the drop-down menu, select the workload to add.
    2. Click Save.

2.6.3. Understanding how to update secrets

When you modify the value of a secret, the value (used by an already running pod) will not dynamically change. To change a secret, you must delete the original pod and create a new pod (perhaps with an identical PodSpec).

Updating a secret follows the same workflow as deploying a new Container image. You can use the kubectl rolling-update command.

The resourceVersion value in a secret is not specified when it is referenced. Therefore, if a secret is updated at the same time as pods are starting, the version of the secret that is used for the pod is not defined.

Note

Currently, it is not possible to check the resource version of a secret object that was used when a pod was created. It is planned that pods will report this information, so that a controller could restart ones using an old resourceVersion. In the interim, do not update the data of existing secrets, but create new ones with distinct names.

2.6.4. Creating and using secrets

As an administrator, you can create a service account token secret. This allows you to distribute a service account token to applications that must authenticate to the API.

Procedure

  1. Create a service account in your namespace by running the following command:

    $ oc create sa <service_account_name> -n <your_namespace>
  2. Save the following YAML example to a file named service-account-token-secret.yaml. The example includes a Secret object configuration that you can use to generate a service account token:

    apiVersion: v1
    kind: Secret
    metadata:
      name: <secret_name> 1
      annotations:
        kubernetes.io/service-account.name: "sa-name" 2
    type: kubernetes.io/service-account-token 3
    1
    Replace <secret_name> with the name of your service token secret.
    2
    Specifies an existing service account name. If you are creating both the ServiceAccount and the Secret objects, create the ServiceAccount object first.
    3
    Specifies a service account token secret type.
  3. Generate the service account token by applying the file:

    $ oc apply -f service-account-token-secret.yaml
  4. Get the service account token from the secret by running the following command:

    $ oc get secret <sa_token_secret> -o jsonpath='{.data.token}' | base64 --decode 1

    Example output

    ayJhbGciOiJSUzI1NiIsImtpZCI6IklOb2dtck1qZ3hCSWpoNnh5YnZhSE9QMkk3YnRZMVZoclFfQTZfRFp1YlUifQ.eyJpc3MiOiJrdWJlcm5ldGVzL3NlcnZpY2VhY2NvdW50Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9uYW1lc3BhY2UiOiJkZWZhdWx0Iiwia3ViZXJuZXRlcy5pby9zZXJ2aWNlYWNjb3VudC9zZWNyZXQubmFtZSI6ImJ1aWxkZXItdG9rZW4tdHZrbnIiLCJrdWJlcm5ldGVzLmlvL3NlcnZpY2VhY2NvdW50L3NlcnZpY2UtYWNjb3VudC5uYW1lIjoiYnVpbGRlciIsImt1YmVybmV0ZXMuaW8vc2VydmljZWFjY291bnQvc2VydmljZS1hY2NvdW50LnVpZCI6IjNmZGU2MGZmLTA1NGYtNDkyZi04YzhjLTNlZjE0NDk3MmFmNyIsInN1YiI6InN5c3RlbTpzZXJ2aWNlYWNjb3VudDpkZWZhdWx0OmJ1aWxkZXIifQ.OmqFTDuMHC_lYvvEUrjr1x453hlEEHYcxS9VKSzmRkP1SiVZWPNPkTWlfNRp6bIUZD3U6aN3N7dMSN0eI5hu36xPgpKTdvuckKLTCnelMx6cxOdAbrcw1mCmOClNscwjS1KO1kzMtYnnq8rXHiMJELsNlhnRyyIXRTtNBsy4t64T3283s3SLsancyx0gy0ujx-Ch3uKAKdZi5iT-I8jnnQ-ds5THDs2h65RJhgglQEmSxpHrLGZFmyHAQI-_SjvmHZPXEc482x3SkaQHNLqpmrpJorNqh1M8ZHKzlujhZgVooMvJmWPXTb2vnvi3DGn2XI-hZxl1yD2yGH1RBpYUHA

    1
    Replace <sa_token_secret> with the name of your service token secret.
  5. Use your service account token to authenticate with the API of your cluster:

    $ curl -X GET <openshift_cluster_api> --header "Authorization: Bearer <token>" 1 2
    1
    Replace <openshift_cluster_api> with the OpenShift cluster API.
    2
    Replace <token> with the service account token that is output in the preceding command.

2.6.5. About using signed certificates with secrets

To secure communication to your service, you can configure OpenShift Container Platform to generate a signed serving certificate/key pair that you can add into a secret in a project.

A service serving certificate secret is intended to support complex middleware applications that need out-of-the-box certificates. It has the same settings as the server certificates generated by the administrator tooling for nodes and masters.

Service Pod spec configured for a service serving certificates secret.

apiVersion: v1
kind: Service
metadata:
  name: registry
  annotations:
    service.beta.openshift.io/serving-cert-secret-name: registry-cert1
# ...

1
Specify the name for the certificate

Other pods can trust cluster-created certificates (which are only signed for internal DNS names), by using the CA bundle in the /var/run/secrets/kubernetes.io/serviceaccount/service-ca.crt file that is automatically mounted in their pod.

The signature algorithm for this feature is x509.SHA256WithRSA. To manually rotate, delete the generated secret. A new certificate is created.

2.6.5.1. Generating signed certificates for use with secrets

To use a signed serving certificate/key pair with a pod, create or edit the service to add the service.beta.openshift.io/serving-cert-secret-name annotation, then add the secret to the pod.

Procedure

To create a service serving certificate secret:

  1. Edit the Pod spec for your service.
  2. Add the service.beta.openshift.io/serving-cert-secret-name annotation with the name you want to use for your secret.

    kind: Service
    apiVersion: v1
    metadata:
      name: my-service
      annotations:
          service.beta.openshift.io/serving-cert-secret-name: my-cert 1
    spec:
      selector:
        app: MyApp
      ports:
      - protocol: TCP
        port: 80
        targetPort: 9376

    The certificate and key are in PEM format, stored in tls.crt and tls.key respectively.

  3. Create the service:

    $ oc create -f <file-name>.yaml
  4. View the secret to make sure it was created:

    1. View a list of all secrets:

      $ oc get secrets

      Example output

      NAME                     TYPE                                  DATA      AGE
      my-cert                  kubernetes.io/tls                     2         9m

    2. View details on your secret:

      $ oc describe secret my-cert

      Example output

      Name:         my-cert
      Namespace:    openshift-console
      Labels:       <none>
      Annotations:  service.beta.openshift.io/expiry: 2023-03-08T23:22:40Z
                    service.beta.openshift.io/originating-service-name: my-service
                    service.beta.openshift.io/originating-service-uid: 640f0ec3-afc2-4380-bf31-a8c784846a11
                    service.beta.openshift.io/expiry: 2023-03-08T23:22:40Z
      
      Type:  kubernetes.io/tls
      
      Data
      ====
      tls.key:  1679 bytes
      tls.crt:  2595 bytes

  5. Edit your Pod spec with that secret.

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-service-pod
    spec:
      containers:
      - name: mypod
        image: redis
        volumeMounts:
        - name: my-container
          mountPath: "/etc/my-path"
      volumes:
      - name: my-volume
        secret:
          secretName: my-cert
          items:
          - key: username
            path: my-group/my-username
            mode: 511

    When it is available, your pod will run. The certificate will be good for the internal service DNS name, <service.name>.<service.namespace>.svc.

    The certificate/key pair is automatically replaced when it gets close to expiration. View the expiration date in the service.beta.openshift.io/expiry annotation on the secret, which is in RFC3339 format.

    Note

    In most cases, the service DNS name <service.name>.<service.namespace>.svc is not externally routable. The primary use of <service.name>.<service.namespace>.svc is for intracluster or intraservice communication, and with re-encrypt routes.

2.6.6. Troubleshooting secrets

If a service certificate generation fails with (service’s service.beta.openshift.io/serving-cert-generation-error annotation contains):

secret/ssl-key references serviceUID 62ad25ca-d703-11e6-9d6f-0e9c0057b608, which does not match 77b6dd80-d716-11e6-9d6f-0e9c0057b60

The service that generated the certificate no longer exists, or has a different serviceUID. You must force certificates regeneration by removing the old secret, and clearing the following annotations on the service service.beta.openshift.io/serving-cert-generation-error, service.beta.openshift.io/serving-cert-generation-error-num:

  1. Delete the secret:

    $ oc delete secret <secret_name>
  2. Clear the annotations:

    $ oc annotate service <service_name> service.beta.openshift.io/serving-cert-generation-error-
    $ oc annotate service <service_name> service.beta.openshift.io/serving-cert-generation-error-num-
Note

The command removing annotation has a - after the annotation name to be removed.

2.7. Creating and using config maps

The following sections define config maps and how to create and use them.

2.7.1. Understanding config maps

Many applications require configuration by using some combination of configuration files, command line arguments, and environment variables. In OpenShift Container Platform, these configuration artifacts are decoupled from image content to keep containerized applications portable.

The ConfigMap object provides mechanisms to inject containers with configuration data while keeping containers agnostic of OpenShift Container Platform. A config map can be used to store fine-grained information like individual properties or coarse-grained information like entire configuration files or JSON blobs.

The ConfigMap object holds key-value pairs of configuration data that can be consumed in pods or used to store configuration data for system components such as controllers. For example:

ConfigMap Object Definition

kind: ConfigMap
apiVersion: v1
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: example-config
  namespace: my-namespace
data: 1
  example.property.1: hello
  example.property.2: world
  example.property.file: |-
    property.1=value-1
    property.2=value-2
    property.3=value-3
binaryData:
  bar: L3Jvb3QvMTAw 2

1 1
Contains the configuration data.
2
Points to a file that contains non-UTF8 data, for example, a binary Java keystore file. Enter the file data in Base 64.
Note

You can use the binaryData field when you create a config map from a binary file, such as an image.

Configuration data can be consumed in pods in a variety of ways. A config map can be used to:

  • Populate environment variable values in containers
  • Set command-line arguments in a container
  • Populate configuration files in a volume

Users and system components can store configuration data in a config map.

A config map is similar to a secret, but designed to more conveniently support working with strings that do not contain sensitive information.

Config map restrictions

A config map must be created before its contents can be consumed in pods.

Controllers can be written to tolerate missing configuration data. Consult individual components configured by using config maps on a case-by-case basis.

ConfigMap objects reside in a project.

They can only be referenced by pods in the same project.

The Kubelet only supports the use of a config map for pods it gets from the API server.

This includes any pods created by using the CLI, or indirectly from a replication controller. It does not include pods created by using the OpenShift Container Platform node’s --manifest-url flag, its --config flag, or its REST API because these are not common ways to create pods.

2.7.2. Creating a config map in the OpenShift Container Platform web console

You can create a config map in the OpenShift Container Platform web console.

Procedure

  • To create a config map as a cluster administrator:

    1. In the Administrator perspective, select WorkloadsConfig Maps.
    2. At the top right side of the page, select Create Config Map.
    3. Enter the contents of your config map.
    4. Select Create.
  • To create a config map as a developer:

    1. In the Developer perspective, select Config Maps.
    2. At the top right side of the page, select Create Config Map.
    3. Enter the contents of your config map.
    4. Select Create.

2.7.3. Creating a config map by using the CLI

You can use the following command to create a config map from directories, specific files, or literal values.

Procedure

  • Create a config map:

    $ oc create configmap <configmap_name> [options]
2.7.3.1. Creating a config map from a directory

You can create a config map from a directory by using the --from-file flag. This method allows you to use multiple files within a directory to create a config map.

Each file in the directory is used to populate a key in the config map, where the name of the key is the file name, and the value of the key is the content of the file.

For example, the following command creates a config map with the contents of the example-files directory:

$ oc create configmap game-config --from-file=example-files/

View the keys in the config map:

$ oc describe configmaps game-config

Example output

Name:           game-config
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data

game.properties:        158 bytes
ui.properties:          83 bytes

You can see that the two keys in the map are created from the file names in the directory specified in the command. The content of those keys might be large, so the output of oc describe only shows the names of the keys and their sizes.

Prerequisite

  • You must have a directory with files that contain the data you want to populate a config map with.

    The following procedure uses these example files: game.properties and ui.properties:

    $ cat example-files/game.properties

    Example output

    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30

    $ cat example-files/ui.properties

    Example output

    color.good=purple
    color.bad=yellow
    allow.textmode=true
    how.nice.to.look=fairlyNice

Procedure

  • Create a config map holding the content of each file in this directory by entering the following command:

    $ oc create configmap game-config \
        --from-file=example-files/

Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys:

    $ oc get configmaps game-config -o yaml

    Example output

    apiVersion: v1
    data:
      game.properties: |-
        enemies=aliens
        lives=3
        enemies.cheat=true
        enemies.cheat.level=noGoodRotten
        secret.code.passphrase=UUDDLRLRBABAS
        secret.code.allowed=true
        secret.code.lives=30
      ui.properties: |
        color.good=purple
        color.bad=yellow
        allow.textmode=true
        how.nice.to.look=fairlyNice
    kind: ConfigMap
    metadata:
      creationTimestamp: 2016-02-18T18:34:05Z
      name: game-config
      namespace: default
      resourceVersion: "407"
      selflink: /api/v1/namespaces/default/configmaps/game-config
      uid: 30944725-d66e-11e5-8cd0-68f728db1985

2.7.3.2. Creating a config map from a file

You can create a config map from a file by using the --from-file flag. You can pass the --from-file option multiple times to the CLI.

You can also specify the key to set in a config map for content imported from a file by passing a key=value expression to the --from-file option. For example:

$ oc create configmap game-config-3 --from-file=game-special-key=example-files/game.properties
Note

If you create a config map from a file, you can include files containing non-UTF8 data that are placed in this field without corrupting the non-UTF8 data. OpenShift Container Platform detects binary files and transparently encodes the file as MIME. On the server, the MIME payload is decoded and stored without corrupting the data.

Prerequisite

  • You must have a directory with files that contain the data you want to populate a config map with.

    The following procedure uses these example files: game.properties and ui.properties:

    $ cat example-files/game.properties

    Example output

    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30

    $ cat example-files/ui.properties

    Example output

    color.good=purple
    color.bad=yellow
    allow.textmode=true
    how.nice.to.look=fairlyNice

Procedure

  • Create a config map by specifying a specific file:

    $ oc create configmap game-config-2 \
        --from-file=example-files/game.properties \
        --from-file=example-files/ui.properties
  • Create a config map by specifying a key-value pair:

    $ oc create configmap game-config-3 \
        --from-file=game-special-key=example-files/game.properties

Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys from the file:

    $ oc get configmaps game-config-2 -o yaml

    Example output

    apiVersion: v1
    data:
      game.properties: |-
        enemies=aliens
        lives=3
        enemies.cheat=true
        enemies.cheat.level=noGoodRotten
        secret.code.passphrase=UUDDLRLRBABAS
        secret.code.allowed=true
        secret.code.lives=30
      ui.properties: |
        color.good=purple
        color.bad=yellow
        allow.textmode=true
        how.nice.to.look=fairlyNice
    kind: ConfigMap
    metadata:
      creationTimestamp: 2016-02-18T18:52:05Z
      name: game-config-2
      namespace: default
      resourceVersion: "516"
      selflink: /api/v1/namespaces/default/configmaps/game-config-2
      uid: b4952dc3-d670-11e5-8cd0-68f728db1985

  • Enter the oc get command for the object with the -o option to see the values of the keys from the key-value pair:

    $ oc get configmaps game-config-3 -o yaml

    Example output

    apiVersion: v1
    data:
      game-special-key: |- 1
        enemies=aliens
        lives=3
        enemies.cheat=true
        enemies.cheat.level=noGoodRotten
        secret.code.passphrase=UUDDLRLRBABAS
        secret.code.allowed=true
        secret.code.lives=30
    kind: ConfigMap
    metadata:
      creationTimestamp: 2016-02-18T18:54:22Z
      name: game-config-3
      namespace: default
      resourceVersion: "530"
      selflink: /api/v1/namespaces/default/configmaps/game-config-3
      uid: 05f8da22-d671-11e5-8cd0-68f728db1985

    1
    This is the key that you set in the preceding step.
2.7.3.3. Creating a config map from literal values

You can supply literal values for a config map.

The --from-literal option takes a key=value syntax, which allows literal values to be supplied directly on the command line.

Procedure

  • Create a config map by specifying a literal value:

    $ oc create configmap special-config \
        --from-literal=special.how=very \
        --from-literal=special.type=charm

Verification

  • Enter the oc get command for the object with the -o option to see the values of the keys:

    $ oc get configmaps special-config -o yaml

    Example output

    apiVersion: v1
    data:
      special.how: very
      special.type: charm
    kind: ConfigMap
    metadata:
      creationTimestamp: 2016-02-18T19:14:38Z
      name: special-config
      namespace: default
      resourceVersion: "651"
      selflink: /api/v1/namespaces/default/configmaps/special-config
      uid: dadce046-d673-11e5-8cd0-68f728db1985

2.7.4. Use cases: Consuming config maps in pods

The following sections describe some uses cases when consuming ConfigMap objects in pods.

2.7.4.1. Populating environment variables in containers by using config maps

You can use config maps to populate individual environment variables in containers or to populate environment variables in containers from all keys that form valid environment variable names.

As an example, consider the following config map:

ConfigMap with two environment variables

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config 1
  namespace: default 2
data:
  special.how: very 3
  special.type: charm 4

1
Name of the config map.
2
The project in which the config map resides. Config maps can only be referenced by pods in the same project.
3 4
Environment variables to inject.

ConfigMap with one environment variable

apiVersion: v1
kind: ConfigMap
metadata:
  name: env-config 1
  namespace: default
data:
  log_level: INFO 2

1
Name of the config map.
2
Environment variable to inject.

Procedure

  • You can consume the keys of this ConfigMap in a pod using configMapKeyRef sections.

    Sample Pod specification configured to inject specific environment variables

    apiVersion: v1
    kind: Pod
    metadata:
      name: dapi-test-pod
    spec:
      containers:
        - name: test-container
          image: gcr.io/google_containers/busybox
          command: [ "/bin/sh", "-c", "env" ]
          env: 1
            - name: SPECIAL_LEVEL_KEY 2
              valueFrom:
                configMapKeyRef:
                  name: special-config 3
                  key: special.how 4
            - name: SPECIAL_TYPE_KEY
              valueFrom:
                configMapKeyRef:
                  name: special-config 5
                  key: special.type 6
                  optional: true 7
          envFrom: 8
            - configMapRef:
                name: env-config 9
      restartPolicy: Never

    1
    Stanza to pull the specified environment variables from a ConfigMap.
    2
    Name of a pod environment variable that you are injecting a key’s value into.
    3 5
    Name of the ConfigMap to pull specific environment variables from.
    4 6
    Environment variable to pull from the ConfigMap.
    7
    Makes the environment variable optional. As optional, the pod will be started even if the specified ConfigMap and keys do not exist.
    8
    Stanza to pull all environment variables from a ConfigMap.
    9
    Name of the ConfigMap to pull all environment variables from.

    When this pod is run, the pod logs will include the following output:

    SPECIAL_LEVEL_KEY=very
    log_level=INFO
Note

SPECIAL_TYPE_KEY=charm is not listed in the example output because optional: true is set.

2.7.4.2. Setting command-line arguments for container commands with config maps

You can use a config map to set the value of the commands or arguments in a container by using the Kubernetes substitution syntax $(VAR_NAME).

As an example, consider the following config map:

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  special.how: very
  special.type: charm

Procedure

  • To inject values into a command in a container, you must consume the keys you want to use as environment variables. Then you can refer to them in a container’s command using the $(VAR_NAME) syntax.

    Sample pod specification configured to inject specific environment variables

    apiVersion: v1
    kind: Pod
    metadata:
      name: dapi-test-pod
    spec:
      containers:
        - name: test-container
          image: gcr.io/google_containers/busybox
          command: [ "/bin/sh", "-c", "echo $(SPECIAL_LEVEL_KEY) $(SPECIAL_TYPE_KEY)" ] 1
          env:
            - name: SPECIAL_LEVEL_KEY
              valueFrom:
                configMapKeyRef:
                  name: special-config
                  key: special.how
            - name: SPECIAL_TYPE_KEY
              valueFrom:
                configMapKeyRef:
                  name: special-config
                  key: special.type
      restartPolicy: Never

    1
    Inject the values into a command in a container using the keys you want to use as environment variables.

    When this pod is run, the output from the echo command run in the test-container container is as follows:

    very charm
2.7.4.3. Injecting content into a volume by using config maps

You can inject content into a volume by using config maps.

Example ConfigMap custom resource (CR)

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  special.how: very
  special.type: charm

Procedure

You have a couple different options for injecting content into a volume by using config maps.

  • The most basic way to inject content into a volume by using a config map is to populate the volume with files where the key is the file name and the content of the file is the value of the key:

    apiVersion: v1
    kind: Pod
    metadata:
      name: dapi-test-pod
    spec:
      containers:
        - name: test-container
          image: gcr.io/google_containers/busybox
          command: [ "/bin/sh", "-c", "cat", "/etc/config/special.how" ]
          volumeMounts:
          - name: config-volume
            mountPath: /etc/config
      volumes:
        - name: config-volume
          configMap:
            name: special-config 1
      restartPolicy: Never
    1
    File containing key.

    When this pod is run, the output of the cat command will be:

    very
  • You can also control the paths within the volume where config map keys are projected:

    apiVersion: v1
    kind: Pod
    metadata:
      name: dapi-test-pod
    spec:
      containers:
        - name: test-container
          image: gcr.io/google_containers/busybox
          command: [ "/bin/sh", "-c", "cat", "/etc/config/path/to/special-key" ]
          volumeMounts:
          - name: config-volume
            mountPath: /etc/config
      volumes:
        - name: config-volume
          configMap:
            name: special-config
            items:
            - key: special.how
              path: path/to/special-key 1
      restartPolicy: Never
    1
    Path to config map key.

    When this pod is run, the output of the cat command will be:

    very

2.8. Using device plugins to access external resources with pods

Device plugins allow you to use a particular device type (GPU, InfiniBand, or other similar computing resources that require vendor-specific initialization and setup) in your OpenShift Container Platform pod without needing to write custom code.

2.8.1. Understanding device plugins

The device plugin provides a consistent and portable solution to consume hardware devices across clusters. The device plugin provides support for these devices through an extension mechanism, which makes these devices available to Containers, provides health checks of these devices, and securely shares them.

Important

OpenShift Container Platform supports the device plugin API, but the device plugin Containers are supported by individual vendors.

A device plugin is a gRPC service running on the nodes (external to the kubelet) that is responsible for managing specific hardware resources. Any device plugin must support following remote procedure calls (RPCs):

service DevicePlugin {
      // GetDevicePluginOptions returns options to be communicated with Device
      // Manager
      rpc GetDevicePluginOptions(Empty) returns (DevicePluginOptions) {}

      // ListAndWatch returns a stream of List of Devices
      // Whenever a Device state change or a Device disappears, ListAndWatch
      // returns the new list
      rpc ListAndWatch(Empty) returns (stream ListAndWatchResponse) {}

      // Allocate is called during container creation so that the Device
      // Plug-in can run device specific operations and instruct Kubelet
      // of the steps to make the Device available in the container
      rpc Allocate(AllocateRequest) returns (AllocateResponse) {}

      // PreStartcontainer is called, if indicated by Device Plug-in during
      // registration phase, before each container start. Device plug-in
      // can run device specific operations such as resetting the device
      // before making devices available to the container
      rpc PreStartcontainer(PreStartcontainerRequest) returns (PreStartcontainerResponse) {}
}
Example device plugins
Note

For easy device plugin reference implementation, there is a stub device plugin in the Device Manager code: vendor/k8s.io/kubernetes/pkg/kubelet/cm/deviceplugin/device_plugin_stub.go.

2.8.1.1. Methods for deploying a device plugin
  • Daemon sets are the recommended approach for device plugin deployments.
  • Upon start, the device plugin will try to create a UNIX domain socket at /var/lib/kubelet/device-plugin/ on the node to serve RPCs from Device Manager.
  • Since device plugins must manage hardware resources, access to the host file system, as well as socket creation, they must be run in a privileged security context.
  • More specific details regarding deployment steps can be found with each device plugin implementation.

2.8.2. Understanding the Device Manager

Device Manager provides a mechanism for advertising specialized node hardware resources with the help of plugins known as device plugins.

You can advertise specialized hardware without requiring any upstream code changes.

Important

OpenShift Container Platform supports the device plugin API, but the device plugin Containers are supported by individual vendors.

Device Manager advertises devices as Extended Resources. User pods can consume devices, advertised by Device Manager, using the same Limit/Request mechanism, which is used for requesting any other Extended Resource.

Upon start, the device plugin registers itself with Device Manager invoking Register on the /var/lib/kubelet/device-plugins/kubelet.sock and starts a gRPC service at /var/lib/kubelet/device-plugins/<plugin>.sock for serving Device Manager requests.

Device Manager, while processing a new registration request, invokes ListAndWatch remote procedure call (RPC) at the device plugin service. In response, Device Manager gets a list of Device objects from the plugin over a gRPC stream. Device Manager will keep watching on the stream for new updates from the plugin. On the plugin side, the plugin will also keep the stream open and whenever there is a change in the state of any of the devices, a new device list is sent to the Device Manager over the same streaming connection.

While handling a new pod admission request, Kubelet passes requested Extended Resources to the Device Manager for device allocation. Device Manager checks in its database to verify if a corresponding plugin exists or not. If the plugin exists and there are free allocatable devices as well as per local cache, Allocate RPC is invoked at that particular device plugin.

Additionally, device plugins can also perform several other device-specific operations, such as driver installation, device initialization, and device resets. These functionalities vary from implementation to implementation.

2.8.3. Enabling Device Manager

Enable Device Manager to implement a device plugin to advertise specialized hardware without any upstream code changes.

Device Manager provides a mechanism for advertising specialized node hardware resources with the help of plugins known as device plugins.

  1. Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command. Perform one of the following steps:

    1. View the machine config:

      # oc describe machineconfig <name>

      For example:

      # oc describe machineconfig 00-worker

      Example output

      Name:         00-worker
      Namespace:
      Labels:       machineconfiguration.openshift.io/role=worker 1

      1
      Label required for the Device Manager.

Procedure

  1. Create a custom resource (CR) for your configuration change.

    Sample configuration for a Device Manager CR

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: devicemgr 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
           machineconfiguration.openshift.io: devicemgr 2
      kubeletConfig:
        feature-gates:
          - DevicePlugins=true 3

    1
    Assign a name to CR.
    2
    Enter the label from the Machine Config Pool.
    3
    Set DevicePlugins to 'true`.
  2. Create the Device Manager:

    $ oc create -f devicemgr.yaml

    Example output

    kubeletconfig.machineconfiguration.openshift.io/devicemgr created

  3. Ensure that Device Manager was actually enabled by confirming that /var/lib/kubelet/device-plugins/kubelet.sock is created on the node. This is the UNIX domain socket on which the Device Manager gRPC server listens for new plugin registrations. This sock file is created when the Kubelet is started only if Device Manager is enabled.

2.9. Including pod priority in pod scheduling decisions

You can enable pod priority and preemption in your cluster. Pod priority indicates the importance of a pod relative to other pods and queues the pods based on that priority. pod preemption allows the cluster to evict, or preempt, lower-priority pods so that higher-priority pods can be scheduled if there is no available space on a suitable node pod priority also affects the scheduling order of pods and out-of-resource eviction ordering on the node.

To use priority and preemption, you create priority classes that define the relative weight of your pods. Then, reference a priority class in the pod specification to apply that weight for scheduling.

2.9.1. Understanding pod priority

When you use the Pod Priority and Preemption feature, the scheduler orders pending pods by their priority, and a pending pod is placed ahead of other pending pods with lower priority in the scheduling queue. As a result, the higher priority pod might be scheduled sooner than pods with lower priority if its scheduling requirements are met. If a pod cannot be scheduled, scheduler continues to schedule other lower priority pods.

2.9.1.1. Pod priority classes

You can assign pods a priority class, which is a non-namespaced object that defines a mapping from a name to the integer value of the priority. The higher the value, the higher the priority.

A priority class object can take any 32-bit integer value smaller than or equal to 1000000000 (one billion). Reserve numbers larger than or equal to one billion for critical pods that must not be preempted or evicted. By default, OpenShift Container Platform has two reserved priority classes for critical system pods to have guaranteed scheduling.

$ oc get priorityclasses

Example output

NAME                      VALUE        GLOBAL-DEFAULT   AGE
system-node-critical      2000001000   false            72m
system-cluster-critical   2000000000   false            72m
openshift-user-critical   1000000000   false            3d13h
cluster-logging           1000000      false            29s

  • system-node-critical - This priority class has a value of 2000001000 and is used for all pods that should never be evicted from a node. Examples of pods that have this priority class are sdn-ovs, sdn, and so forth. A number of critical components include the system-node-critical priority class by default, for example:

    • master-api
    • master-controller
    • master-etcd
    • sdn
    • sdn-ovs
    • sync
  • system-cluster-critical - This priority class has a value of 2000000000 (two billion) and is used with pods that are important for the cluster. Pods with this priority class can be evicted from a node in certain circumstances. For example, pods configured with the system-node-critical priority class can take priority. However, this priority class does ensure guaranteed scheduling. Examples of pods that can have this priority class are fluentd, add-on components like descheduler, and so forth. A number of critical components include the system-cluster-critical priority class by default, for example:

    • fluentd
    • metrics-server
    • descheduler
  • openshift-user-critical - You can use the priorityClassName field with important pods that cannot bind their resource consumption and do not have predictable resource consumption behavior. Prometheus pods under the openshift-monitoring and openshift-user-workload-monitoring namespaces use the openshift-user-critical priorityClassName. Monitoring workloads use system-critical as their first priorityClass, but this causes problems when monitoring uses excessive memory and the nodes cannot evict them. As a result, monitoring drops priority to give the scheduler flexibility, moving heavy workloads around to keep critical nodes operating.
  • cluster-logging - This priority is used by Fluentd to make sure Fluentd pods are scheduled to nodes over other apps.
2.9.1.2. Pod priority names

After you have one or more priority classes, you can create pods that specify a priority class name in a Pod spec. The priority admission controller uses the priority class name field to populate the integer value of the priority. If the named priority class is not found, the pod is rejected.

2.9.2. Understanding pod preemption

When a developer creates a pod, the pod goes into a queue. If the developer configured the pod for pod priority or preemption, the scheduler picks a pod from the queue and tries to schedule the pod on a node. If the scheduler cannot find space on an appropriate node that satisfies all the specified requirements of the pod, preemption logic is triggered for the pending pod.

When the scheduler preempts one or more pods on a node, the nominatedNodeName field of higher-priority Pod spec is set to the name of the node, along with the nodename field. The scheduler uses the nominatedNodeName field to keep track of the resources reserved for pods and also provides information to the user about preemptions in the clusters.

After the scheduler preempts a lower-priority pod, the scheduler honors the graceful termination period of the pod. If another node becomes available while scheduler is waiting for the lower-priority pod to terminate, the scheduler can schedule the higher-priority pod on that node. As a result, the nominatedNodeName field and nodeName field of the Pod spec might be different.

Also, if the scheduler preempts pods on a node and is waiting for termination, and a pod with a higher-priority pod than the pending pod needs to be scheduled, the scheduler can schedule the higher-priority pod instead. In such a case, the scheduler clears the nominatedNodeName of the pending pod, making the pod eligible for another node.

Preemption does not necessarily remove all lower-priority pods from a node. The scheduler can schedule a pending pod by removing a portion of the lower-priority pods.

The scheduler considers a node for pod preemption only if the pending pod can be scheduled on the node.

2.9.2.1. Non-preempting priority classes

Pods with the preemption policy set to Never are placed in the scheduling queue ahead of lower-priority pods, but they cannot preempt other pods. A non-preempting pod waiting to be scheduled stays in the scheduling queue until sufficient resources are free and it can be scheduled. Non-preempting pods, like other pods, are subject to scheduler back-off. This means that if the scheduler tries unsuccessfully to schedule these pods, they are retried with lower frequency, allowing other pods with lower priority to be scheduled before them.

Non-preempting pods can still be preempted by other, high-priority pods.

2.9.2.2. Pod preemption and other scheduler settings

If you enable pod priority and preemption, consider your other scheduler settings:

Pod priority and pod disruption budget
A pod disruption budget specifies the minimum number or percentage of replicas that must be up at a time. If you specify pod disruption budgets, OpenShift Container Platform respects them when preempting pods at a best effort level. The scheduler attempts to preempt pods without violating the pod disruption budget. If no such pods are found, lower-priority pods might be preempted despite their pod disruption budget requirements.
Pod priority and pod affinity
Pod affinity requires a new pod to be scheduled on the same node as other pods with the same label.

If a pending pod has inter-pod affinity with one or more of the lower-priority pods on a node, the scheduler cannot preempt the lower-priority pods without violating the affinity requirements. In this case, the scheduler looks for another node to schedule the pending pod. However, there is no guarantee that the scheduler can find an appropriate node and pending pod might not be scheduled.

To prevent this situation, carefully configure pod affinity with equal-priority pods.

2.9.2.3. Graceful termination of preempted pods

When preempting a pod, the scheduler waits for the pod graceful termination period to expire, allowing the pod to finish working and exit. If the pod does not exit after the period, the scheduler kills the pod. This graceful termination period creates a time gap between the point that the scheduler preempts the pod and the time when the pending pod can be scheduled on the node.

To minimize this gap, configure a small graceful termination period for lower-priority pods.

2.9.3. Configuring priority and preemption

You apply pod priority and preemption by creating a priority class object and associating pods to the priority by using the priorityClassName in your pod specs.

Note

You cannot add a priority class directly to an existing scheduled pod.

Procedure

To configure your cluster to use priority and preemption:

  1. Create one or more priority classes:

    1. Create a YAML file similar to the following:

      apiVersion: scheduling.k8s.io/v1
      kind: PriorityClass
      metadata:
        name: high-priority 1
      value: 1000000 2
      preemptionPolicy: PreemptLowerPriority 3
      globalDefault: false 4
      description: "This priority class should be used for XYZ service pods only." 5
      1
      The name of the priority class object.
      2
      The priority value of the object.
      3
      Optional. Specifies whether this priority class is preempting or non-preempting. The preemption policy defaults to PreemptLowerPriority, which allows pods of that priority class to preempt lower-priority pods. If the preemption policy is set to Never, pods in that priority class are non-preempting.
      4
      Optional. Specifies whether this priority class should be used for pods without a priority class name specified. This field is false by default. Only one priority class with globalDefault set to true can exist in the cluster. If there is no priority class with globalDefault:true, the priority of pods with no priority class name is zero. Adding a priority class with globalDefault:true affects only pods created after the priority class is added and does not change the priorities of existing pods.
      5
      Optional. Describes which pods developers should use with this priority class. Enter an arbitrary text string.
    2. Create the priority class:

      $ oc create -f <file-name>.yaml
  2. Create a pod spec to include the name of a priority class:

    1. Create a YAML file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: nginx
        labels:
          env: test
      spec:
        containers:
        - name: nginx
          image: nginx
          imagePullPolicy: IfNotPresent
        priorityClassName: high-priority 1
      1
      Specify the priority class to use with this pod.
    2. Create the pod:

      $ oc create -f <file-name>.yaml

      You can add the priority name directly to the pod configuration or to a pod template.

2.10. Placing pods on specific nodes using node selectors

A node selector specifies a map of key-value pairs. The rules are defined using custom labels on nodes and selectors specified in pods.

For the pod to be eligible to run on a node, the pod must have the indicated key-value pairs as the label on the node.

If you are using node affinity and node selectors in the same pod configuration, see the important considerations below.

2.10.1. Using node selectors to control pod placement

You can use node selectors on pods and labels on nodes to control where the pod is scheduled. With node selectors, OpenShift Container Platform schedules the pods on nodes that contain matching labels.

You add labels to a node, a compute machine set, or a machine config. Adding the label to the compute machine set ensures that if the node or machine goes down, new nodes have the label. Labels added to a node or machine config do not persist if the node or machine goes down.

To add node selectors to an existing pod, add a node selector to the controlling object for that pod, such as a ReplicaSet object, DaemonSet object, StatefulSet object, Deployment object, or DeploymentConfig object. Any existing pods under that controlling object are recreated on a node with a matching label. If you are creating a new pod, you can add the node selector directly to the pod spec. If the pod does not have a controlling object, you must delete the pod, edit the pod spec, and recreate the pod.

Note

You cannot add a node selector directly to an existing scheduled pod.

Prerequisites

To add a node selector to existing pods, determine the controlling object for that pod. For example, the router-default-66d5cf9464-m2g75 pod is controlled by the router-default-66d5cf9464 replica set:

$ oc describe pod router-default-66d5cf9464-7pwkc

Example output

kind: Pod
apiVersion: v1
metadata:
#...
Name:               router-default-66d5cf9464-7pwkc
Namespace:          openshift-ingress
# ...
Controlled By:      ReplicaSet/router-default-66d5cf9464
# ...

The web console lists the controlling object under ownerReferences in the pod YAML:

apiVersion: v1
kind: Pod
metadata:
  name: router-default-66d5cf9464-7pwkc
# ...
  ownerReferences:
    - apiVersion: apps/v1
      kind: ReplicaSet
      name: router-default-66d5cf9464
      uid: d81dd094-da26-11e9-a48a-128e7edf0312
      controller: true
      blockOwnerDeletion: true
# ...

Procedure

  1. Add labels to a node by using a compute machine set or editing the node directly:

    • Use a MachineSet object to add labels to nodes managed by the compute machine set when a node is created:

      1. Run the following command to add labels to a MachineSet object:

        $ oc patch MachineSet <name> --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"<key>"="<value>","<key>"="<value>"}}]'  -n openshift-machine-api

        For example:

        $ oc patch MachineSet abc612-msrtw-worker-us-east-1c  --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"type":"user-node","region":"east"}}]'  -n openshift-machine-api
        Tip

        You can alternatively apply the following YAML to add labels to a compute machine set:

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        metadata:
          name: xf2bd-infra-us-east-2a
          namespace: openshift-machine-api
        spec:
          template:
            spec:
              metadata:
                labels:
                  region: "east"
                  type: "user-node"
        #...
      2. Verify that the labels are added to the MachineSet object by using the oc edit command:

        For example:

        $ oc edit MachineSet abc612-msrtw-worker-us-east-1c -n openshift-machine-api

        Example MachineSet object

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        
        # ...
        
        spec:
        # ...
          template:
            metadata:
        # ...
            spec:
              metadata:
                labels:
                  region: east
                  type: user-node
        # ...

    • Add labels directly to a node:

      1. Edit the Node object for the node:

        $ oc label nodes <name> <key>=<value>

        For example, to label a node:

        $ oc label nodes ip-10-0-142-25.ec2.internal type=user-node region=east
        Tip

        You can alternatively apply the following YAML to add labels to a node:

        kind: Node
        apiVersion: v1
        metadata:
          name: hello-node-6fbccf8d9
          labels:
            type: "user-node"
            region: "east"
        #...
      2. Verify that the labels are added to the node:

        $ oc get nodes -l type=user-node,region=east

        Example output

        NAME                          STATUS   ROLES    AGE   VERSION
        ip-10-0-142-25.ec2.internal   Ready    worker   17m   v1.25.0

  2. Add the matching node selector to a pod:

    • To add a node selector to existing and future pods, add a node selector to the controlling object for the pods:

      Example ReplicaSet object with labels

      kind: ReplicaSet
      apiVersion: apps/v1
      metadata:
        name: hello-node-6fbccf8d9
      # ...
      spec:
      # ...
        template:
          metadata:
            creationTimestamp: null
            labels:
              ingresscontroller.operator.openshift.io/deployment-ingresscontroller: default
              pod-template-hash: 66d5cf9464
          spec:
            nodeSelector:
              kubernetes.io/os: linux
              node-role.kubernetes.io/worker: ''
              type: user-node 1
      #...

      1
      Add the node selector.
    • To add a node selector to a specific, new pod, add the selector to the Pod object directly:

      Example Pod object with a node selector

      apiVersion: v1
      kind: Pod
      metadata:
        name: hello-node-6fbccf8d9
      #...
      spec:
        nodeSelector:
          region: east
          type: user-node
      #...

      Note

      You cannot add a node selector directly to an existing scheduled pod.

Chapter 3. Automatically scaling pods with the Custom Metrics Autoscaler Operator

3.1. Release notes

3.1.1. Custom Metrics Autoscaler Operator release notes

The release notes for the Custom Metrics Autoscaler Operator for Red Hat OpenShift describe new features and enhancements, deprecated features, and known issues.

The Custom Metrics Autoscaler Operator uses the Kubernetes-based Event Driven Autoscaler (KEDA) and is built on top of the OpenShift Container Platform horizontal pod autoscaler (HPA).

Note

The Custom Metrics Autoscaler Operator for Red Hat OpenShift is provided as an installable component, with a distinct release cycle from the core OpenShift Container Platform. The Red Hat OpenShift Container Platform Life Cycle Policy outlines release compatibility.

3.1.1.1. Supported versions

The following table defines the Custom Metrics Autoscaler Operator versions for each OpenShift Container Platform version.

VersionOpenShift Container Platform versionGeneral availability

2.14.1

4.16

General availability

2.14.1

4.15

General availability

2.14.1

4.14

General availability

2.14.1

4.13

General availability

2.14.1

4.12

General availability

3.1.1.2. Custom Metrics Autoscaler Operator 2.14.1-467 release notes

This release of the Custom Metrics Autoscaler Operator 2.14.1-467 provides a CVE and a bug fix for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHSA-2024:7348.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of Kubernetes-based Event Driven Autoscaler (KEDA).

3.1.1.2.1. Bug fixes
  • Previously, the root file system of the Custom Metrics Autoscaler Operator pod was writable, which is unnecessary and could present security issues. This update makes the pod root file system read-only, which addresses the potential security issue. (OCPBUGS-37989)

3.1.2. Release notes for past releases of the Custom Metrics Autoscaler Operator

The following release notes are for previous versions of the Custom Metrics Autoscaler Operator.

For the current version, see Custom Metrics Autoscaler Operator release notes.

3.1.2.1. Custom Metrics Autoscaler Operator 2.14.1-454 release notes

This release of the Custom Metrics Autoscaler Operator 2.14.1-454 provides a CVE, a new feature, and bug fixes for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHBA-2024:5865.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of Kubernetes-based Event Driven Autoscaler (KEDA).

3.1.2.1.1. New features and enhancements
3.1.2.1.1.1. Support for the Cron trigger with the Custom Metrics Autoscaler Operator

The Custom Metrics Autoscaler Operator can now use the Cron trigger to scale pods based on an hourly schedule. When your specified time frame starts, the Custom Metrics Autoscaler Operator scales pods to your desired amount. When the time frame ends, the Operator scales back down to the previous level.

For more information, see Understanding the Cron trigger.

3.1.2.1.2. Bug fixes
  • Previously, if you made changes to audit configuration parameters in the KedaController custom resource, the keda-metrics-server-audit-policy config map would not get updated. As a consequence, you could not change the audit configuration parameters after the initial deployment of the Custom Metrics Autoscaler. With this fix, changes to the audit configuration now render properly in the config map, allowing you to change the audit configuration any time after installation. (OCPBUGS-32521)
3.1.2.2. Custom Metrics Autoscaler Operator 2.13.1 release notes

This release of the Custom Metrics Autoscaler Operator 2.13.1-421 provides a new feature and a bug fix for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHBA-2024:4837.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of Kubernetes-based Event Driven Autoscaler (KEDA).

3.1.2.2.1. New features and enhancements
3.1.2.2.1.1. Support for custom certificates with the Custom Metrics Autoscaler Operator

The Custom Metrics Autoscaler Operator can now use custom service CA certificates to connect securely to TLS-enabled metrics sources, such as an external Kafka cluster or an external Prometheus service. By default, the Operator uses automatically-generated service certificates to connect to on-cluster services only. There is a new field in the KedaController object that allows you to load custom server CA certificates for connecting to external services by using config maps.

For more information, see Custom CA certificates for the Custom Metrics Autoscaler.

3.1.2.2.2. Bug fixes
  • Previously, the custom-metrics-autoscaler and custom-metrics-autoscaler-adapter images were missing time zone information. As a consequence, scaled objects with cron triggers failed to work because the controllers were unable to find time zone information. With this fix, the image builds are updated to include time zone information. As a result, scaled objects containing cron triggers now function properly. Scaled objects containing cron triggers are currently not supported for the custom metrics autoscaler. (OCPBUGS-34018)
3.1.2.3. Custom Metrics Autoscaler Operator 2.12.1-394 release notes

This release of the Custom Metrics Autoscaler Operator 2.12.1-394 provides a bug fix for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHSA-2024:2901.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of Kubernetes-based Event Driven Autoscaler (KEDA).

3.1.2.3.1. Bug fixes
  • Previously, the protojson.Unmarshal function entered into an infinite loop when unmarshaling certain forms of invalid JSON. This condition could occur when unmarshaling into a message that contains a google.protobuf.Any value or when the UnmarshalOptions.DiscardUnknown option is set. This release fixes this issue. (OCPBUGS-30305)
  • Previously, when parsing a multipart form, either explicitly with the Request.ParseMultipartForm method or implicitly with the Request.FormValue, Request.PostFormValue, or Request.FormFile method, the limits on the total size of the parsed form were not applied to the memory consumed. This could cause memory exhaustion. With this fix, the parsing process now correctly limits the maximum size of form lines while reading a single form line. (OCPBUGS-30360)
  • Previously, when following an HTTP redirect to a domain that is not on a matching subdomain or on an exact match of the initial domain, an HTTP client would not forward sensitive headers, such as Authorization or Cookie. For example, a redirect from example.com to www.example.com would forward the Authorization header, but a redirect to www.example.org would not forward the header. This release fixes this issue. (OCPBUGS-30365)
  • Previously, verifying a certificate chain that contains a certificate with an unknown public key algorithm caused the certificate verification process to panic. This condition affected all crypto and Transport Layer Security (TLS) clients and servers that set the Config.ClientAuth parameter to the VerifyClientCertIfGiven or RequireAndVerifyClientCert value. The default behavior is for TLS servers to not verify client certificates. This release fixes this issue. (OCPBUGS-30370)
  • Previously, if errors returned from the MarshalJSON method contained user-controlled data, an attacker could have used the data to break the contextual auto-escaping behavior of the HTML template package. This condition would allow for subsequent actions to inject unexpected content into the templates. This release fixes this issue. (OCPBUGS-30397)
  • Previously, the net/http and golang.org/x/net/http2 Go packages did not limit the number of CONTINUATION frames for an HTTP/2 request. This condition could result in excessive CPU consumption. This release fixes this issue. (OCPBUGS-30894)
3.1.2.4. Custom Metrics Autoscaler Operator 2.12.1-384 release notes

This release of the Custom Metrics Autoscaler Operator 2.12.1-384 provides a bug fix for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHBA-2024:2043.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.4.1. Bug fixes
  • Previously, the custom-metrics-autoscaler and custom-metrics-autoscaler-adapter images were missing time zone information. As a consequence, scaled objects with cron triggers failed to work because the controllers were unable to find time zone information. With this fix, the image builds are updated to include time zone information. As a result, scaled objects containing cron triggers now function properly. (OCPBUGS-32395)
3.1.2.5. Custom Metrics Autoscaler Operator 2.12.1-376 release notes

This release of the Custom Metrics Autoscaler Operator 2.12.1-376 provides security updates and bug fixes for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHSA-2024:1812.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.5.1. Bug fixes
  • Previously, if invalid values such as nonexistent namespaces were specified in scaled object metadata, the underlying scaler clients would not free, or close, their client descriptors, resulting in a slow memory leak. This fix properly closes the underlying client descriptors when there are errors, preventing memory from leaking. (OCPBUGS-30145)
  • Previously the ServiceMonitor custom resource (CR) for the keda-metrics-apiserver pod was not functioning, because the CR referenced an incorrect metrics port name of http. This fix corrects the ServiceMonitor CR to reference the proper port name of metrics. As a result, the Service Monitor functions properly. (OCPBUGS-25806)
3.1.2.6. Custom Metrics Autoscaler Operator 2.11.2-322 release notes

This release of the Custom Metrics Autoscaler Operator 2.11.2-322 provides security updates and bug fixes for running the Operator in an OpenShift Container Platform cluster. The following advisory is available for the RHSA-2023:6144.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.6.1. Bug fixes
  • Because the Custom Metrics Autoscaler Operator version 3.11.2-311 was released without a required volume mount in the Operator deployment, the Custom Metrics Autoscaler Operator pod would restart every 15 minutes. This fix adds the required volume mount to the Operator deployment. As a result, the Operator no longer restarts every 15 minutes. (OCPBUGS-22361)
3.1.2.7. Custom Metrics Autoscaler Operator 2.11.2-311 release notes

This release of the Custom Metrics Autoscaler Operator 2.11.2-311 provides new features and bug fixes for running the Operator in an OpenShift Container Platform cluster. The components of the Custom Metrics Autoscaler Operator 2.11.2-311 were released in RHBA-2023:5981.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.7.1. New features and enhancements
3.1.2.7.1.1. Red Hat OpenShift Service on AWS (ROSA) and OpenShift Dedicated are now supported

The Custom Metrics Autoscaler Operator 2.11.2-311 can be installed on OpenShift ROSA and OpenShift Dedicated managed clusters. Previous versions of the Custom Metrics Autoscaler Operator could be installed only in the openshift-keda namespace. This prevented the Operator from being installed on OpenShift ROSA and OpenShift Dedicated clusters. This version of Custom Metrics Autoscaler allows installation to other namespaces such as openshift-operators or keda, enabling installation into ROSA and Dedicated clusters.

3.1.2.7.2. Bug fixes
  • Previously, if the Custom Metrics Autoscaler Operator was installed and configured, but not in use, the OpenShift CLI reported the couldn’t get resource list for external.metrics.k8s.io/v1beta1: Got empty response for: external.metrics.k8s.io/v1beta1 error after any oc command was entered. The message, although harmless, could have caused confusion. With this fix, the Got empty response for: external.metrics…​ error no longer appears inappropriately. (OCPBUGS-15779)
  • Previously, any annotation or label change to objects managed by the Custom Metrics Autoscaler were reverted by Custom Metrics Autoscaler Operator any time the Keda Controller was modified, for example after a configuration change. This caused continuous changing of labels in your objects. The Custom Metrics Autoscaler now uses its own annotation to manage labels and annotations, and annotation or label are no longer inappropriately reverted. (OCPBUGS-15590)
3.1.2.8. Custom Metrics Autoscaler Operator 2.10.1-267 release notes

This release of the Custom Metrics Autoscaler Operator 2.10.1-267 provides new features and bug fixes for running the Operator in an OpenShift Container Platform cluster. The components of the Custom Metrics Autoscaler Operator 2.10.1-267 were released in RHBA-2023:4089.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.8.1. Bug fixes
  • Previously, the custom-metrics-autoscaler and custom-metrics-autoscaler-adapter images did not contain time zone information. Because of this, scaled objects with cron triggers failed to work because the controllers were unable to find time zone information. With this fix, the image builds now include time zone information. As a result, scaled objects containing cron triggers now function properly. (OCPBUGS-15264)
  • Previously, the Custom Metrics Autoscaler Operator would attempt to take ownership of all managed objects, including objects in other namespaces and cluster-scoped objects. Because of this, the Custom Metrics Autoscaler Operator was unable to create the role binding for reading the credentials necessary to be an API server. This caused errors in the kube-system namespace. With this fix, the Custom Metrics Autoscaler Operator skips adding the ownerReference field to any object in another namespace or any cluster-scoped object. As a result, the role binding is now created without any errors. (OCPBUGS-15038)
  • Previously, the Custom Metrics Autoscaler Operator added an ownerReferences field to the openshift-keda namespace. While this did not cause functionality problems, the presence of this field could have caused confusion for cluster administrators. With this fix, the Custom Metrics Autoscaler Operator does not add the ownerReference field to the openshift-keda namespace. As a result, the openshift-keda namespace no longer has a superfluous ownerReference field. (OCPBUGS-15293)
  • Previously, if you used a Prometheus trigger configured with authentication method other than pod identity, and the podIdentity parameter was set to none, the trigger would fail to scale. With this fix, the Custom Metrics Autoscaler for OpenShift now properly handles the none pod identity provider type. As a result, a Prometheus trigger configured with authentication method other than pod identity, and the podIdentity parameter sset to none now properly scales. (OCPBUGS-15274)
3.1.2.9. Custom Metrics Autoscaler Operator 2.10.1 release notes

This release of the Custom Metrics Autoscaler Operator 2.10.1 provides new features and bug fixes for running the Operator in an OpenShift Container Platform cluster. The components of the Custom Metrics Autoscaler Operator 2.10.1 were released in RHEA-2023:3199.

Important

Before installing this version of the Custom Metrics Autoscaler Operator, remove any previously installed Technology Preview versions or the community-supported version of KEDA.

3.1.2.9.1. New features and enhancements
3.1.2.9.1.1. Custom Metrics Autoscaler Operator general availability

The Custom Metrics Autoscaler Operator is now generally available as of Custom Metrics Autoscaler Operator version 2.10.1.

Important

Scaling by using a scaled job is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

3.1.2.9.1.2. Performance metrics

You can now use the Prometheus Query Language (PromQL) to query metrics on the Custom Metrics Autoscaler Operator.

3.1.2.9.1.3. Pausing the custom metrics autoscaling for scaled objects

You can now pause the autoscaling of a scaled object, as needed, and resume autoscaling when ready.

3.1.2.9.1.4. Replica fall back for scaled objects

You can now specify the number of replicas to fall back to if a scaled object fails to get metrics from the source.

3.1.2.9.1.5. Customizable HPA naming for scaled objects

You can now specify a custom name for the horizontal pod autoscaler in scaled objects.

3.1.2.9.1.6. Activation and scaling thresholds

Because the horizontal pod autoscaler (HPA) cannot scale to or from 0 replicas, the Custom Metrics Autoscaler Operator does that scaling, after which the HPA performs the scaling. You can now specify when the HPA takes over autoscaling, based on the number of replicas. This allows for more flexibility with your scaling policies.

3.1.2.10. Custom Metrics Autoscaler Operator 2.8.2-174 release notes

This release of the Custom Metrics Autoscaler Operator 2.8.2-174 provides new features and bug fixes for running the Operator in an OpenShift Container Platform cluster. The components of the Custom Metrics Autoscaler Operator 2.8.2-174 were released in RHEA-2023:1683.

Important

The Custom Metrics Autoscaler Operator version 2.8.2-174 is a Technology Preview feature.

3.1.2.10.1. New features and enhancements
3.1.2.10.1.1. Operator upgrade support

You can now upgrade from a prior version of the Custom Metrics Autoscaler Operator. See "Changing the update channel for an Operator" in the "Additional resources" for information on upgrading an Operator.

3.1.2.10.1.2. must-gather support

You can now collect data about the Custom Metrics Autoscaler Operator and its components by using the OpenShift Container Platform must-gather tool. Currently, the process for using the must-gather tool with the Custom Metrics Autoscaler is different than for other operators. See "Gathering debugging data in the "Additional resources" for more information.

3.1.2.11. Custom Metrics Autoscaler Operator 2.8.2 release notes

This release of the Custom Metrics Autoscaler Operator 2.8.2 provides new features and bug fixes for running the Operator in an OpenShift Container Platform cluster. The components of the Custom Metrics Autoscaler Operator 2.8.2 were released in RHSA-2023:1042.

Important

The Custom Metrics Autoscaler Operator version 2.8.2 is a Technology Preview feature.

3.1.2.11.1. New features and enhancements
3.1.2.11.1.1. Audit Logging

You can now gather and view audit logs for the Custom Metrics Autoscaler Operator and its associated components. Audit logs are security-relevant chronological sets of records that document the sequence of activities that have affected the system by individual users, administrators, or other components of the system.

3.1.2.11.1.2. Scale applications based on Apache Kafka metrics

You can now use the KEDA Apache kafka trigger/scaler to scale deployments based on an Apache Kafka topic.

3.1.2.11.1.3. Scale applications based on CPU metrics

You can now use the KEDA CPU trigger/scaler to scale deployments based on CPU metrics.

3.1.2.11.1.4. Scale applications based on memory metrics

You can now use the KEDA memory trigger/scaler to scale deployments based on memory metrics.

3.2. Custom Metrics Autoscaler Operator overview

As a developer, you can use Custom Metrics Autoscaler Operator for Red Hat OpenShift to specify how OpenShift Container Platform should automatically increase or decrease the number of pods for a deployment, stateful set, custom resource, or job based on custom metrics that are not based only on CPU or memory.

The Custom Metrics Autoscaler Operator is an optional Operator, based on the Kubernetes Event Driven Autoscaler (KEDA), that allows workloads to be scaled using additional metrics sources other than pod metrics.

The custom metrics autoscaler currently supports only the Prometheus, CPU, memory, and Apache Kafka metrics.

The Custom Metrics Autoscaler Operator scales your pods up and down based on custom, external metrics from specific applications. Your other applications continue to use other scaling methods. You configure triggers, also known as scalers, which are the source of events and metrics that the custom metrics autoscaler uses to determine how to scale. The custom metrics autoscaler uses a metrics API to convert the external metrics to a form that OpenShift Container Platform can use. The custom metrics autoscaler creates a horizontal pod autoscaler (HPA) that performs the actual scaling.

To use the custom metrics autoscaler, you create a ScaledObject or ScaledJob object for a workload, which is a custom resource (CR) that defines the scaling metadata. You specify the deployment or job to scale, the source of the metrics to scale on (trigger), and other parameters such as the minimum and maximum replica counts allowed.

Note

You can create only one scaled object or scaled job for each workload that you want to scale. Also, you cannot use a scaled object or scaled job and the horizontal pod autoscaler (HPA) on the same workload.

The custom metrics autoscaler, unlike the HPA, can scale to zero. If you set the minReplicaCount value in the custom metrics autoscaler CR to 0, the custom metrics autoscaler scales the workload down from 1 to 0 replicas to or up from 0 replicas to 1. This is known as the activation phase. After scaling up to 1 replica, the HPA takes control of the scaling. This is known as the scaling phase.

Some triggers allow you to change the number of replicas that are scaled by the cluster metrics autoscaler. In all cases, the parameter to configure the activation phase always uses the same phrase, prefixed with activation. For example, if the threshold parameter configures scaling, activationThreshold would configure activation. Configuring the activation and scaling phases allows you more flexibility with your scaling policies. For example, you can configure a higher activation phase to prevent scaling up or down if the metric is particularly low.

The activation value has more priority than the scaling value in case of different decisions for each. For example, if the threshold is set to 10, and the activationThreshold is 50, if the metric reports 40, the scaler is not active and the pods are scaled to zero even if the HPA requires 4 instances.

Figure 3.1. Custom metrics autoscaler workflow

Custom metrics autoscaler workflow
  1. You create or modify a scaled object custom resource for a workload on a cluster. The object contains the scaling configuration for that workload. Prior to accepting the new object, the OpenShift API server sends it to the custom metrics autoscaler admission webhooks process to ensure that the object is valid. If validation succeeds, the API server persists the object.
  2. The custom metrics autoscaler controller watches for new or modified scaled objects. When the OpenShift API server notifies the controller of a change, the controller monitors any external trigger sources, also known as data sources, that are specified in the object for changes to the metrics data. One or more scalers request scaling data from the external trigger source. For example, for a Kafka trigger type, the controller uses the Kafka scaler to communicate with a Kafka instance to obtain the data requested by the trigger.
  3. The controller creates a horizontal pod autoscaler object for the scaled object. As a result, the Horizontal Pod Autoscaler (HPA) Operator starts monitoring the scaling data associated with the trigger. The HPA requests scaling data from the cluster OpenShift API server endpoint.
  4. The OpenShift API server endpoint is served by the custom metrics autoscaler metrics adapter. When the metrics adapter receives a request for custom metrics, it uses a GRPC connection to the controller to request it for the most recent trigger data received from the scaler.
  5. The HPA makes scaling decisions based upon the data received from the metrics adapter and scales the workload up or down by increasing or decreasing the replicas.
  6. As a it operates, a workload can affect the scaling metrics. For example, if a workload is scaled up to handle work in a Kafka queue, the queue size decreases after the workload processes all the work. As a result, the workload is scaled down.
  7. If the metrics are in a range specified by the minReplicaCount value, the custom metrics autoscaler controller disables all scaling, and leaves the replica count at a fixed level. If the metrics exceed that range, the custom metrics autoscaler controller enables scaling and allows the HPA to scale the workload. While scaling is disabled, the HPA does not take any action.

3.2.1. Custom CA certificates for the Custom Metrics Autoscaler

By default, the Custom Metrics Autoscaler Operator uses automatically-generated service CA certificates to connect to on-cluster services.

If you want to use off-cluster services that require custom CA certificates, you can add the required certificates to a config map. Then, add the config map to the KedaController custom resource as described in Installing the custom metrics autoscaler. The Operator loads those certificates on start-up and registers them as trusted by the Operator.

The config maps can contain one or more certificate files that contain one or more PEM-encoded CA certificates. Or, you can use separate config maps for each certificate file.

Note

If you later update the config map to add additional certificates, you must restart the keda-operator-* pod for the changes to take effect.

3.3. Installing the custom metrics autoscaler

You can use the OpenShift Container Platform web console to install the Custom Metrics Autoscaler Operator.

The installation creates the following five CRDs:

  • ClusterTriggerAuthentication
  • KedaController
  • ScaledJob
  • ScaledObject
  • TriggerAuthentication

3.3.1. Installing the custom metrics autoscaler

You can use the following procedure to install the Custom Metrics Autoscaler Operator.

Prerequisites

  • Remove any previously-installed Technology Preview versions of the Cluster Metrics Autoscaler Operator.
  • Remove any versions of the community-based KEDA.

    Also, remove the KEDA 1.x custom resource definitions by running the following commands:

    $ oc delete crd scaledobjects.keda.k8s.io
    $ oc delete crd triggerauthentications.keda.k8s.io
  • Optional: If you need the Custom Metrics Autoscaler Operator to connect to off-cluster services, such as an external Kafka cluster or an external Prometheus service, put any required service CA certificates into a config map. The config map must exist in the same namespace where the Operator is installed. For example:

    $ oc create configmap -n openshift-keda thanos-cert  --from-file=ca-cert.pem

Procedure

  1. In the OpenShift Container Platform web console, click OperatorsOperatorHub.
  2. Choose Custom Metrics Autoscaler from the list of available Operators, and click Install.
  3. On the Install Operator page, ensure that the All namespaces on the cluster (default) option is selected for Installation Mode. This installs the Operator in all namespaces.
  4. Ensure that the openshift-keda namespace is selected for Installed Namespace. OpenShift Container Platform creates the namespace, if not present in your cluster.
  5. Click Install.
  6. Verify the installation by listing the Custom Metrics Autoscaler Operator components:

    1. Navigate to WorkloadsPods.
    2. Select the openshift-keda project from the drop-down menu and verify that the custom-metrics-autoscaler-operator-* pod is running.
    3. Navigate to WorkloadsDeployments to verify that the custom-metrics-autoscaler-operator deployment is running.
  7. Optional: Verify the installation in the OpenShift CLI using the following commands:

    $ oc get all -n openshift-keda

    The output appears similar to the following:

    Example output

    NAME                                                      READY   STATUS    RESTARTS   AGE
    pod/custom-metrics-autoscaler-operator-5fd8d9ffd8-xt4xp   1/1     Running   0          18m
    
    NAME                                                 READY   UP-TO-DATE   AVAILABLE   AGE
    deployment.apps/custom-metrics-autoscaler-operator   1/1     1            1           18m
    
    NAME                                                            DESIRED   CURRENT   READY   AGE
    replicaset.apps/custom-metrics-autoscaler-operator-5fd8d9ffd8   1         1         1       18m

  8. Install the KedaController custom resource, which creates the required CRDs:

    1. In the OpenShift Container Platform web console, click OperatorsInstalled Operators.
    2. Click Custom Metrics Autoscaler.
    3. On the Operator Details page, click the KedaController tab.
    4. On the KedaController tab, click Create KedaController and edit the file.

      kind: KedaController
      apiVersion: keda.sh/v1alpha1
      metadata:
        name: keda
        namespace: openshift-keda
      spec:
        watchNamespace: '' 1
        operator:
          logLevel: info 2
          logEncoder: console 3
          caConfigMaps: 4
          - thanos-cert
          - kafka-cert
        metricsServer:
          logLevel: '0' 5
          auditConfig: 6
            logFormat: "json"
            logOutputVolumeClaim: "persistentVolumeClaimName"
            policy:
              rules:
              - level: Metadata
              omitStages: ["RequestReceived"]
              omitManagedFields: false
            lifetime:
              maxAge: "2"
              maxBackup: "1"
              maxSize: "50"
        serviceAccount: {}
      1
      Specifies a single namespace in which the Custom Metrics Autoscaler Operator should scale applications. Leave it blank or leave it empty to scale applications in all namespaces. This field should have a namespace or be empty. The default value is empty.
      2
      Specifies the level of verbosity for the Custom Metrics Autoscaler Operator log messages. The allowed values are debug, info, error. The default is info.
      3
      Specifies the logging format for the Custom Metrics Autoscaler Operator log messages. The allowed values are console or json. The default is console.
      4
      Optional: Specifies one or more config maps with CA certificates, which the Custom Metrics Autoscaler Operator can use to connect securely to TLS-enabled metrics sources.
      5
      Specifies the logging level for the Custom Metrics Autoscaler Metrics Server. The allowed values are 0 for info and 4 or debug. The default is 0.
      6
      Activates audit logging for the Custom Metrics Autoscaler Operator and specifies the audit policy to use, as described in the "Configuring audit logging" section.
    5. Click Create to create the KEDA controller.

3.4. Understanding custom metrics autoscaler triggers

Triggers, also known as scalers, provide the metrics that the Custom Metrics Autoscaler Operator uses to scale your pods.

The custom metrics autoscaler currently supports only the Prometheus, CPU, memory, and Apache Kafka triggers.

You use a ScaledObject or ScaledJob custom resource to configure triggers for specific objects, as described in the sections that follow.

You can configure a certificate authority to use with your scaled objects or for all scalers in the cluster.

3.4.1. Understanding the Prometheus trigger

You can scale pods based on Prometheus metrics, which can use the installed OpenShift Container Platform monitoring or an external Prometheus server as the metrics source. See "Configuring the custom metrics autoscaler to use OpenShift Container Platform monitoring" for information on the configurations required to use the OpenShift Container Platform monitoring as a source for metrics.

Note

If Prometheus is collecting metrics from the application that the custom metrics autoscaler is scaling, do not set the minimum replicas to 0 in the custom resource. If there are no application pods, the custom metrics autoscaler does not have any metrics to scale on.

Example scaled object with a Prometheus target

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: prom-scaledobject
  namespace: my-namespace
spec:
# ...
  triggers:
  - type: prometheus 1
    metadata:
      serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092 2
      namespace: kedatest 3
      metricName: http_requests_total 4
      threshold: '5' 5
      query: sum(rate(http_requests_total{job="test-app"}[1m])) 6
      authModes: basic 7
      cortexOrgID: my-org 8
      ignoreNullValues: false 9
      unsafeSsl: false 10

1
Specifies Prometheus as the trigger type.
2
Specifies the address of the Prometheus server. This example uses OpenShift Container Platform monitoring.
3
Optional: Specifies the namespace of the object you want to scale. This parameter is mandatory if using OpenShift Container Platform monitoring as a source for the metrics.
4
Specifies the name to identify the metric in the external.metrics.k8s.io API. If you are using more than one trigger, all metric names must be unique.
5
Specifies the value that triggers scaling. Must be specified as a quoted string value.
6
Specifies the Prometheus query to use.
7
Specifies the authentication method to use. Prometheus scalers support bearer authentication (bearer), basic authentication (basic), or TLS authentication (tls). You configure the specific authentication parameters in a trigger authentication, as discussed in a following section. As needed, you can also use a secret.
8
Optional: Passes the X-Scope-OrgID header to multi-tenant Cortex or Mimir storage for Prometheus. This parameter is required only with multi-tenant Prometheus storage, to indicate which data Prometheus should return.
9
Optional: Specifies how the trigger should proceed if the Prometheus target is lost.
  • If true, the trigger continues to operate if the Prometheus target is lost. This is the default behavior.
  • If false, the trigger returns an error if the Prometheus target is lost.
10
Optional: Specifies whether the certificate check should be skipped. For example, you might skip the check if you are running in a test environment and using self-signed certificates at the Prometheus endpoint.
  • If false, the certificate check is performed. This is the default behavior.
  • If true, the certificate check is not performed.

    Important

    Skipping the check is not recommended.

3.4.1.1. Configuring the custom metrics autoscaler to use OpenShift Container Platform monitoring

You can use the installed OpenShift Container Platform Prometheus monitoring as a source for the metrics used by the custom metrics autoscaler. However, there are some additional configurations you must perform.

Note

These steps are not required for an external Prometheus source.

You must perform the following tasks, as described in this section:

  • Create a service account to get a token.
  • Create a role.
  • Add that role to the service account.
  • Reference the token in the trigger authentication object used by Prometheus.

Prerequisites

  • OpenShift Container Platform monitoring must be installed.
  • Monitoring of user-defined workloads must be enabled in OpenShift Container Platform monitoring, as described in the Creating a user-defined workload monitoring config map section.
  • The Custom Metrics Autoscaler Operator must be installed.

Procedure

  1. Change to the project with the object you want to scale:

    $ oc project my-project
  2. Use the following command to create a service account, if your cluster does not have one:

    $ oc create serviceaccount <service_account>

    where:

    <service_account>
    Specifies the name of the service account.
  3. Use the following command to locate the token assigned to the service account:

    $ oc describe serviceaccount <service_account>

    where:

    <service_account>
    Specifies the name of the service account.

    Example output

    Name:                thanos
    Namespace:           my-project
    Labels:              <none>
    Annotations:         <none>
    Image pull secrets:  thanos-dockercfg-nnwgj
    Mountable secrets:   thanos-dockercfg-nnwgj
    Tokens:              thanos-token-9g4n5 1
    Events:              <none>

    1
    Use this token in the trigger authentication.
  4. Create a trigger authentication with the service account token:

    1. Create a YAML file similar to the following:

      apiVersion: keda.sh/v1alpha1
      kind: TriggerAuthentication
      metadata:
        name: keda-trigger-auth-prometheus
      spec:
        secretTargetRef: 1
        - parameter: bearerToken 2
          name: thanos-token-9g4n5 3
          key: token 4
        - parameter: ca
          name: thanos-token-9g4n5
          key: ca.crt
      1
      Specifies that this object uses a secret for authorization.
      2
      Specifies the authentication parameter to supply by using the token.
      3
      Specifies the name of the token to use.
      4
      Specifies the key in the token to use with the specified parameter.
    2. Create the CR object:

      $ oc create -f <file-name>.yaml
  5. Create a role for reading Thanos metrics:

    1. Create a YAML file with the following parameters:

      apiVersion: rbac.authorization.k8s.io/v1
      kind: Role
      metadata:
        name: thanos-metrics-reader
      rules:
      - apiGroups:
        - ""
        resources:
        - pods
        verbs:
        - get
      - apiGroups:
        - metrics.k8s.io
        resources:
        - pods
        - nodes
        verbs:
        - get
        - list
        - watch
    2. Create the CR object:

      $ oc create -f <file-name>.yaml
  6. Create a role binding for reading Thanos metrics:

    1. Create a YAML file similar to the following:

      apiVersion: rbac.authorization.k8s.io/v1
      kind: RoleBinding
      metadata:
        name: thanos-metrics-reader 1
        namespace: my-project 2
      roleRef:
        apiGroup: rbac.authorization.k8s.io
        kind: Role
        name: thanos-metrics-reader
      subjects:
      - kind: ServiceAccount
        name: thanos 3
        namespace: my-project 4
      1
      Specifies the name of the role you created.
      2
      Specifies the namespace of the object you want to scale.
      3
      Specifies the name of the service account to bind to the role.
      4
      Specifies the namespace of the object you want to scale.
    2. Create the CR object:

      $ oc create -f <file-name>.yaml

You can now deploy a scaled object or scaled job to enable autoscaling for your application, as described in "Understanding how to add custom metrics autoscalers". To use OpenShift Container Platform monitoring as the source, in the trigger, or scaler, you must include the following parameters:

  • triggers.type must be prometheus
  • triggers.metadata.serverAddress must be https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
  • triggers.metadata.authModes must be bearer
  • triggers.metadata.namespace must be set to the namespace of the object to scale
  • triggers.authenticationRef must point to the trigger authentication resource specified in the previous step

3.4.2. Understanding the CPU trigger

You can scale pods based on CPU metrics. This trigger uses cluster metrics as the source for metrics.

The custom metrics autoscaler scales the pods associated with an object to maintain the CPU usage that you specify. The autoscaler increases or decreases the number of replicas between the minimum and maximum numbers to maintain the specified CPU utilization across all pods. The memory trigger considers the memory utilization of the entire pod. If the pod has multiple containers, the memory trigger considers the total memory utilization of all containers in the pod.

Note
  • This trigger cannot be used with the ScaledJob custom resource.
  • When using a memory trigger to scale an object, the object does not scale to 0, even if you are using multiple triggers.

Example scaled object with a CPU target

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: cpu-scaledobject
  namespace: my-namespace
spec:
# ...
  triggers:
  - type: cpu 1
    metricType: Utilization 2
    metadata:
      value: '60' 3
  minReplicaCount: 1 4

1
Specifies CPU as the trigger type.
2
Specifies the type of metric to use, either Utilization or AverageValue.
3
Specifies the value that triggers scaling. Must be specified as a quoted string value.
  • When using Utilization, the target value is the average of the resource metrics across all relevant pods, represented as a percentage of the requested value of the resource for the pods.
  • When using AverageValue, the target value is the average of the metrics across all relevant pods.
4
Specifies the minimum number of replicas when scaling down. For a CPU trigger, enter a value of 1 or greater, because the HPA cannot scale to zero if you are using only CPU metrics.

3.4.3. Understanding the memory trigger

You can scale pods based on memory metrics. This trigger uses cluster metrics as the source for metrics.

The custom metrics autoscaler scales the pods associated with an object to maintain the average memory usage that you specify. The autoscaler increases and decreases the number of replicas between the minimum and maximum numbers to maintain the specified memory utilization across all pods. The memory trigger considers the memory utilization of entire pod. If the pod has multiple containers, the memory utilization is the sum of all of the containers.

Note
  • This trigger cannot be used with the ScaledJob custom resource.
  • When using a memory trigger to scale an object, the object does not scale to 0, even if you are using multiple triggers.

Example scaled object with a memory target

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: memory-scaledobject
  namespace: my-namespace
spec:
# ...
  triggers:
  - type: memory 1
    metricType: Utilization 2
    metadata:
      value: '60' 3
      containerName: api 4

1
Specifies memory as the trigger type.
2
Specifies the type of metric to use, either Utilization or AverageValue.
3
Specifies the value that triggers scaling. Must be specified as a quoted string value.
  • When using Utilization, the target value is the average of the resource metrics across all relevant pods, represented as a percentage of the requested value of the resource for the pods.
  • When using AverageValue, the target value is the average of the metrics across all relevant pods.
4
Optional: Specifies an individual container to scale, based on the memory utilization of only that container, rather than the entire pod. In this example, only the container named api is to be scaled.

3.4.4. Understanding the Kafka trigger

You can scale pods based on an Apache Kafka topic or other services that support the Kafka protocol. The custom metrics autoscaler does not scale higher than the number of Kafka partitions, unless you set the allowIdleConsumers parameter to true in the scaled object or scaled job.

Note

If the number of consumer groups exceeds the number of partitions in a topic, the extra consumer groups remain idle. To avoid this, by default the number of replicas does not exceed:

  • The number of partitions on a topic, if a topic is specified
  • The number of partitions of all topics in the consumer group, if no topic is specified
  • The maxReplicaCount specified in scaled object or scaled job CR

You can use the allowIdleConsumers parameter to disable these default behaviors.

Example scaled object with a Kafka target

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: kafka-scaledobject
  namespace: my-namespace
spec:
# ...
  triggers:
  - type: kafka 1
    metadata:
      topic: my-topic 2
      bootstrapServers: my-cluster-kafka-bootstrap.openshift-operators.svc:9092 3
      consumerGroup: my-group 4
      lagThreshold: '10' 5
      activationLagThreshold: '5' 6
      offsetResetPolicy: latest 7
      allowIdleConsumers: true 8
      scaleToZeroOnInvalidOffset: false 9
      excludePersistentLag: false 10
      version: '1.0.0' 11
      partitionLimitation: '1,2,10-20,31' 12
      tls: enable 13

1
Specifies Kafka as the trigger type.
2
Specifies the name of the Kafka topic on which Kafka is processing the offset lag.
3
Specifies a comma-separated list of Kafka brokers to connect to.
4
Specifies the name of the Kafka consumer group used for checking the offset on the topic and processing the related lag.
5
Optional: Specifies the average target value that triggers scaling. Must be specified as a quoted string value. The default is 5.
6
Optional: Specifies the target value for the activation phase. Must be specified as a quoted string value.
7
Optional: Specifies the Kafka offset reset policy for the Kafka consumer. The available values are: latest and earliest. The default is latest.
8
Optional: Specifies whether the number of Kafka replicas can exceed the number of partitions on a topic.
  • If true, the number of Kafka replicas can exceed the number of partitions on a topic. This allows for idle Kafka consumers.
  • If false, the number of Kafka replicas cannot exceed the number of partitions on a topic. This is the default.
9
Specifies how the trigger behaves when a Kafka partition does not have a valid offset.
  • If true, the consumers are scaled to zero for that partition.
  • If false, the scaler keeps a single consumer for that partition. This is the default.
10
Optional: Specifies whether the trigger includes or excludes partition lag for partitions whose current offset is the same as the current offset of the previous polling cycle.
  • If true, the scaler excludes partition lag in these partitions.
  • If false, the trigger includes all consumer lag in all partitions. This is the default.
11
Optional: Specifies the version of your Kafka brokers. Must be specified as a quoted string value. The default is 1.0.0.
12
Optional: Specifies a comma-separated list of partition IDs to scope the scaling on. If set, only the listed IDs are considered when calculating lag. Must be specified as a quoted string value. The default is to consider all partitions.
13
Optional: Specifies whether to use TSL client authentication for Kafka. The default is disable. For information on configuring TLS, see "Understanding custom metrics autoscaler trigger authentications".

3.4.5. Understanding the Cron trigger

You can scale pods based on a time range.

When the time range starts, the custom metrics autoscaler scales the pods associated with an object from the configured minimum number of pods to the specified number of desired pods. At the end of the time range, the pods are scaled back to the configured minimum. The time period must be configured in cron format.

The following example scales the pods associated with this scaled object from 0 to 100 from 6:00 AM to 6:30 PM India Standard Time.

Example scaled object with a Cron trigger

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: cron-scaledobject
  namespace: default
spec:
  scaleTargetRef:
    name: my-deployment
  minReplicaCount: 0 1
  maxReplicaCount: 100 2
  cooldownPeriod: 300
  triggers:
  - type: cron 3
    metadata:
      timezone: Asia/Kolkata 4
      start: "0 6 * * *" 5
      end: "30 18 * * *" 6
      desiredReplicas: "100" 7

1
Specifies the minimum number of pods to scale down to at the end of the time frame.
2
Specifies the maximum number of replicas when scaling up. This value should be the same as desiredReplicas. The default is 100.
3
Specifies a Cron trigger.
4
Specifies the timezone for the time frame. This value must be from the IANA Time Zone Database.
5
Specifies the start of the time frame.
6
Specifies the end of the time frame.
7
Specifies the number of pods to scale to between the start and end of the time frame. This value should be the same as maxReplicaCount.

3.5. Understanding custom metrics autoscaler trigger authentications

A trigger authentication allows you to include authentication information in a scaled object or a scaled job that can be used by the associated containers. You can use trigger authentications to pass OpenShift Container Platform secrets, platform-native pod authentication mechanisms, environment variables, and so on.

You define a TriggerAuthentication object in the same namespace as the object that you want to scale. That trigger authentication can be used only by objects in that namespace.

Alternatively, to share credentials between objects in multiple namespaces, you can create a ClusterTriggerAuthentication object that can be used across all namespaces.

Trigger authentications and cluster trigger authentication use the same configuration. However, a cluster trigger authentication requires an additional kind parameter in the authentication reference of the scaled object.

Example secret for Basic authentication

apiVersion: v1
kind: Secret
metadata:
  name: my-basic-secret
  namespace: default
data:
  username: "dXNlcm5hbWU=" 1
  password: "cGFzc3dvcmQ="

1
User name and password to supply to the trigger authentication. The values in a data stanza must be base-64 encoded.

Example trigger authentication using a secret for Basic authentication

kind: TriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata:
  name: secret-triggerauthentication
  namespace: my-namespace 1
spec:
  secretTargetRef: 2
  - parameter: username 3
    name: my-basic-secret 4
    key: username 5
  - parameter: password
    name: my-basic-secret
    key: password

1
Specifies the namespace of the object you want to scale.
2
Specifies that this trigger authentication uses a secret for authorization when connecting to the metrics endpoint.
3
Specifies the authentication parameter to supply by using the secret.
4
Specifies the name of the secret to use.
5
Specifies the key in the secret to use with the specified parameter.

Example cluster trigger authentication with a secret for Basic authentication

kind: ClusterTriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata: 1
  name: secret-cluster-triggerauthentication
spec:
  secretTargetRef: 2
  - parameter: username 3
    name: my-basic-secret 4
    key: username 5
  - parameter: password
    name: my-basic-secret
    key: password

1
Note that no namespace is used with a cluster trigger authentication.
2
Specifies that this trigger authentication uses a secret for authorization when connecting to the metrics endpoint.
3
Specifies the authentication parameter to supply by using the secret.
4
Specifies the name of the secret to use.
5
Specifies the key in the secret to use with the specified parameter.

Example secret with certificate authority (CA) details

apiVersion: v1
kind: Secret
metadata:
  name: my-secret
  namespace: my-namespace
data:
  ca-cert.pem: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0tLS0... 1
  client-cert.pem: LS0tLS1CRUdJTiBDRVJUSUZJQ0FURS0... 2
  client-key.pem: LS0tLS1CRUdJTiBQUklWQVRFIEtFWS0t...

1
Specifies the TLS CA Certificate for authentication of the metrics endpoint. The value must be base-64 encoded.
2
Specifies the TLS certificates and key for TLS client authentication. The values must be base-64 encoded.

Example trigger authentication using a secret for CA details

kind: TriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata:
  name: secret-triggerauthentication
  namespace: my-namespace 1
spec:
  secretTargetRef: 2
    - parameter: key 3
      name: my-secret 4
      key: client-key.pem 5
    - parameter: ca 6
      name: my-secret 7
      key: ca-cert.pem 8

1
Specifies the namespace of the object you want to scale.
2
Specifies that this trigger authentication uses a secret for authorization when connecting to the metrics endpoint.
3
Specifies the type of authentication to use.
4
Specifies the name of the secret to use.
5
Specifies the key in the secret to use with the specified parameter.
6
Specifies the authentication parameter for a custom CA when connecting to the metrics endpoint.
7
Specifies the name of the secret to use.
8
Specifies the key in the secret to use with the specified parameter.

Example secret with a bearer token

apiVersion: v1
kind: Secret
metadata:
  name: my-secret
  namespace: my-namespace
data:
  bearerToken: "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXV" 1

1
Specifies a bearer token to use with bearer authentication. The value in a data stanza must be base-64 encoded.

Example trigger authentication with a bearer token

kind: TriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata:
  name: token-triggerauthentication
  namespace: my-namespace 1
spec:
  secretTargetRef: 2
  - parameter: bearerToken 3
    name: my-secret 4
    key: bearerToken 5

1
Specifies the namespace of the object you want to scale.
2
Specifies that this trigger authentication uses a secret for authorization when connecting to the metrics endpoint.
3
Specifies the type of authentication to use.
4
Specifies the name of the secret to use.
5
Specifies the key in the token to use with the specified parameter.

Example trigger authentication with an environment variable

kind: TriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata:
  name: env-var-triggerauthentication
  namespace: my-namespace 1
spec:
  env: 2
  - parameter: access_key 3
    name: ACCESS_KEY 4
    containerName: my-container 5

1
Specifies the namespace of the object you want to scale.
2
Specifies that this trigger authentication uses environment variables for authorization when connecting to the metrics endpoint.
3
Specify the parameter to set with this variable.
4
Specify the name of the environment variable.
5
Optional: Specify a container that requires authentication. The container must be in the same resource as referenced by scaleTargetRef in the scaled object.

Example trigger authentication with pod authentication providers

kind: TriggerAuthentication
apiVersion: keda.sh/v1alpha1
metadata:
  name: pod-id-triggerauthentication
  namespace: my-namespace 1
spec:
  podIdentity: 2
    provider: aws-eks 3

1
Specifies the namespace of the object you want to scale.
2
Specifies that this trigger authentication uses a platform-native pod authentication when connecting to the metrics endpoint.
3
Specifies a pod identity. Supported values are none, azure, gcp, aws-eks, or aws-kiam. The default is none.

Additional resources

3.5.1. Using trigger authentications

You use trigger authentications and cluster trigger authentications by using a custom resource to create the authentication, then add a reference to a scaled object or scaled job.

Prerequisites

  • The Custom Metrics Autoscaler Operator must be installed.
  • If you are using a secret, the Secret object must exist, for example:

    Example secret

    apiVersion: v1
    kind: Secret
    metadata:
      name: my-secret
    data:
      user-name: <base64_USER_NAME>
      password: <base64_USER_PASSWORD>

Procedure

  1. Create the TriggerAuthentication or ClusterTriggerAuthentication object.

    1. Create a YAML file that defines the object:

      Example trigger authentication with a secret

      kind: TriggerAuthentication
      apiVersion: keda.sh/v1alpha1
      metadata:
        name: prom-triggerauthentication
        namespace: my-namespace
      spec:
        secretTargetRef:
        - parameter: user-name
          name: my-secret
          key: USER_NAME
        - parameter: password
          name: my-secret
          key: USER_PASSWORD

    2. Create the TriggerAuthentication object:

      $ oc create -f <filename>.yaml
  2. Create or edit a ScaledObject YAML file that uses the trigger authentication:

    1. Create a YAML file that defines the object by running the following command:

      Example scaled object with a trigger authentication

      apiVersion: keda.sh/v1alpha1
      kind: ScaledObject
      metadata:
        name: scaledobject
        namespace: my-namespace
      spec:
        scaleTargetRef:
          name: example-deployment
        maxReplicaCount: 100
        minReplicaCount: 0
        pollingInterval: 30
        triggers:
        - type: prometheus
          metadata:
            serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
            namespace: kedatest # replace <NAMESPACE>
            metricName: http_requests_total
            threshold: '5'
            query: sum(rate(http_requests_total{job="test-app"}[1m]))
            authModes: "basic"
          authenticationRef:
            name: prom-triggerauthentication 1
            kind: TriggerAuthentication 2

      1
      Specify the name of your trigger authentication object.
      2
      Specify TriggerAuthentication. TriggerAuthentication is the default.

      Example scaled object with a cluster trigger authentication

      apiVersion: keda.sh/v1alpha1
      kind: ScaledObject
      metadata:
        name: scaledobject
        namespace: my-namespace
      spec:
        scaleTargetRef:
          name: example-deployment
        maxReplicaCount: 100
        minReplicaCount: 0
        pollingInterval: 30
        triggers:
        - type: prometheus
          metadata:
            serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
            namespace: kedatest # replace <NAMESPACE>
            metricName: http_requests_total
            threshold: '5'
            query: sum(rate(http_requests_total{job="test-app"}[1m]))
            authModes: "basic"
          authenticationRef:
            name: prom-cluster-triggerauthentication 1
            kind: ClusterTriggerAuthentication 2

      1
      Specify the name of your trigger authentication object.
      2
      Specify ClusterTriggerAuthentication.
    2. Create the scaled object by running the following command:

      $ oc apply -f <filename>

3.6. Pausing the custom metrics autoscaler for a scaled object

You can pause and restart the autoscaling of a workload, as needed.

For example, you might want to pause autoscaling before performing cluster maintenance or to avoid resource starvation by removing non-mission-critical workloads.

3.6.1. Pausing a custom metrics autoscaler

You can pause the autoscaling of a scaled object by adding the autoscaling.keda.sh/paused-replicas annotation to the custom metrics autoscaler for that scaled object. The custom metrics autoscaler scales the replicas for that workload to the specified value and pauses autoscaling until the annotation is removed.

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  annotations:
    autoscaling.keda.sh/paused-replicas: "4"
# ...

Procedure

  1. Use the following command to edit the ScaledObject CR for your workload:

    $ oc edit ScaledObject scaledobject
  2. Add the autoscaling.keda.sh/paused-replicas annotation with any value:

    apiVersion: keda.sh/v1alpha1
    kind: ScaledObject
    metadata:
      annotations:
        autoscaling.keda.sh/paused-replicas: "4" 1
      creationTimestamp: "2023-02-08T14:41:01Z"
      generation: 1
      name: scaledobject
      namespace: my-project
      resourceVersion: '65729'
      uid: f5aec682-acdf-4232-a783-58b5b82f5dd0
    1
    Specifies that the Custom Metrics Autoscaler Operator is to scale the replicas to the specified value and stop autoscaling.

3.6.2. Restarting the custom metrics autoscaler for a scaled object

You can restart a paused custom metrics autoscaler by removing the autoscaling.keda.sh/paused-replicas annotation for that ScaledObject.

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  annotations:
    autoscaling.keda.sh/paused-replicas: "4"
# ...

Procedure

  1. Use the following command to edit the ScaledObject CR for your workload:

    $ oc edit ScaledObject scaledobject
  2. Remove the autoscaling.keda.sh/paused-replicas annotation.

    apiVersion: keda.sh/v1alpha1
    kind: ScaledObject
    metadata:
      annotations:
        autoscaling.keda.sh/paused-replicas: "4" 1
      creationTimestamp: "2023-02-08T14:41:01Z"
      generation: 1
      name: scaledobject
      namespace: my-project
      resourceVersion: '65729'
      uid: f5aec682-acdf-4232-a783-58b5b82f5dd0
    1
    Remove this annotation to restart a paused custom metrics autoscaler.

3.7. Gathering audit logs

You can gather audit logs, which are a security-relevant chronological set of records documenting the sequence of activities that have affected the system by individual users, administrators, or other components of the system.

For example, audit logs can help you understand where an autoscaling request is coming from. This is key information when backends are getting overloaded by autoscaling requests made by user applications and you need to determine which is the troublesome application.

3.7.1. Configuring audit logging

You can configure auditing for the Custom Metrics Autoscaler Operator by editing the KedaController custom resource. The logs are sent to an audit log file on a volume that is secured by using a persistent volume claim in the KedaController CR.

Prerequisites

  • The Custom Metrics Autoscaler Operator must be installed.

Procedure

  1. Edit the KedaController custom resource to add the auditConfig stanza:

    kind: KedaController
    apiVersion: keda.sh/v1alpha1
    metadata:
      name: keda
      namespace: openshift-keda
    spec:
    # ...
      metricsServer:
    # ...
        auditConfig:
          logFormat: "json" 1
          logOutputVolumeClaim: "pvc-audit-log" 2
          policy:
            rules: 3
            - level: Metadata
            omitStages: "RequestReceived" 4
            omitManagedFields: false 5
          lifetime: 6
            maxAge: "2"
            maxBackup: "1"
            maxSize: "50"
    1
    Specifies the output format of the audit log, either legacy or json.
    2
    Specifies an existing persistent volume claim for storing the log data. All requests coming to the API server are logged to this persistent volume claim. If you leave this field empty, the log data is sent to stdout.
    3
    Specifies which events should be recorded and what data they should include:
    • None: Do not log events.
    • Metadata: Log only the metadata for the request, such as user, timestamp, and so forth. Do not log the request text and the response text. This is the default.
    • Request: Log only the metadata and the request text but not the response text. This option does not apply for non-resource requests.
    • RequestResponse: Log event metadata, request text, and response text. This option does not apply for non-resource requests.
    4
    Specifies stages for which no event is created.
    5
    Specifies whether to omit the managed fields of the request and response bodies from being written to the API audit log, either true to omit the fields or false to include the fields.
    6
    Specifies the size and lifespan of the audit logs.
    • maxAge: The maximum number of days to retain audit log files, based on the timestamp encoded in their filename.
    • maxBackup: The maximum number of audit log files to retain. Set to 0 to retain all audit log files.
    • maxSize: The maximum size in megabytes of an audit log file before it gets rotated.

Verification

  1. View the audit log file directly:

    1. Obtain the name of the keda-metrics-apiserver-* pod:

      oc get pod -n openshift-keda

      Example output

      NAME                                                  READY   STATUS    RESTARTS   AGE
      custom-metrics-autoscaler-operator-5cb44cd75d-9v4lv   1/1     Running   0          8m20s
      keda-metrics-apiserver-65c7cc44fd-rrl4r               1/1     Running   0          2m55s
      keda-operator-776cbb6768-zpj5b                        1/1     Running   0          2m55s

    2. View the log data by using a command similar to the following:

      $ oc logs keda-metrics-apiserver-<hash>|grep -i metadata 1
      1
      Optional: You can use the grep command to specify the log level to display: Metadata, Request, RequestResponse.

      For example:

      $ oc logs keda-metrics-apiserver-65c7cc44fd-rrl4r|grep -i metadata

      Example output

       ...
      {"kind":"Event","apiVersion":"audit.k8s.io/v1","level":"Metadata","auditID":"4c81d41b-3dab-4675-90ce-20b87ce24013","stage":"ResponseComplete","requestURI":"/healthz","verb":"get","user":{"username":"system:anonymous","groups":["system:unauthenticated"]},"sourceIPs":["10.131.0.1"],"userAgent":"kube-probe/1.26","responseStatus":{"metadata":{},"code":200},"requestReceivedTimestamp":"2023-02-16T13:00:03.554567Z","stageTimestamp":"2023-02-16T13:00:03.555032Z","annotations":{"authorization.k8s.io/decision":"allow","authorization.k8s.io/reason":""}}
       ...

  2. Alternatively, you can view a specific log:

    1. Use a command similar to the following to log into the keda-metrics-apiserver-* pod:

      $ oc rsh pod/keda-metrics-apiserver-<hash> -n openshift-keda

      For example:

      $ oc rsh pod/keda-metrics-apiserver-65c7cc44fd-rrl4r -n openshift-keda
    2. Change to the /var/audit-policy/ directory:

      sh-4.4$ cd /var/audit-policy/
    3. List the available logs:

      sh-4.4$ ls

      Example output

      log-2023.02.17-14:50  policy.yaml

    4. View the log, as needed:

      sh-4.4$ cat <log_name>/<pvc_name>|grep -i <log_level> 1
      1
      Optional: You can use the grep command to specify the log level to display: Metadata, Request, RequestResponse.

      For example:

      sh-4.4$ cat log-2023.02.17-14:50/pvc-audit-log|grep -i Request

      Example output

       ...
      {"kind":"Event","apiVersion":"audit.k8s.io/v1","level":"Request","auditID":"63e7f68c-04ec-4f4d-8749-bf1656572a41","stage":"ResponseComplete","requestURI":"/openapi/v2","verb":"get","user":{"username":"system:aggregator","groups":["system:authenticated"]},"sourceIPs":["10.128.0.1"],"responseStatus":{"metadata":{},"code":304},"requestReceivedTimestamp":"2023-02-17T13:12:55.035478Z","stageTimestamp":"2023-02-17T13:12:55.038346Z","annotations":{"authorization.k8s.io/decision":"allow","authorization.k8s.io/reason":"RBAC: allowed by ClusterRoleBinding \"system:discovery\" of ClusterRole \"system:discovery\" to Group \"system:authenticated\""}}
       ...

3.8. Gathering debugging data

When opening a support case, it is helpful to provide debugging information about your cluster to Red Hat Support.

To help troubleshoot your issue, provide the following information:

  • Data gathered using the must-gather tool.
  • The unique cluster ID.

You can use the must-gather tool to collect data about the Custom Metrics Autoscaler Operator and its components, including the following items:

  • The openshift-keda namespace and its child objects.
  • The Custom Metric Autoscaler Operator installation objects.
  • The Custom Metric Autoscaler Operator CRD objects.

3.8.1. Gathering debugging data

The following command runs the must-gather tool for the Custom Metrics Autoscaler Operator:

$ oc adm must-gather --image="$(oc get packagemanifests openshift-custom-metrics-autoscaler-operator \
-n openshift-marketplace \
-o jsonpath='{.status.channels[?(@.name=="stable")].currentCSVDesc.annotations.containerImage}')"
Note

The standard OpenShift Container Platform must-gather command, oc adm must-gather, does not collect Custom Metrics Autoscaler Operator data.

Prerequisites

  • Access to the cluster as a user with the cluster-admin role.
  • The OpenShift Container Platform CLI (oc) installed.

Procedure

  1. Navigate to the directory where you want to store the must-gather data.

    Note

    If your cluster is using a restricted network, you must take additional steps. If your mirror registry has a trusted CA, you must first add the trusted CA to the cluster. For all clusters on restricted networks, you must import the default must-gather image as an image stream by running the following command.

    $ oc import-image is/must-gather -n openshift
  2. Perform one of the following:

    • To get only the Custom Metrics Autoscaler Operator must-gather data, use the following command:

      $ oc adm must-gather --image="$(oc get packagemanifests openshift-custom-metrics-autoscaler-operator \
      -n openshift-marketplace \
      -o jsonpath='{.status.channels[?(@.name=="stable")].currentCSVDesc.annotations.containerImage}')"

      The custom image for the must-gather command is pulled directly from the Operator package manifests, so that it works on any cluster where the Custom Metric Autoscaler Operator is available.

    • To gather the default must-gather data in addition to the Custom Metric Autoscaler Operator information:

      1. Use the following command to obtain the Custom Metrics Autoscaler Operator image and set it as an environment variable:

        $ IMAGE="$(oc get packagemanifests openshift-custom-metrics-autoscaler-operator \
          -n openshift-marketplace \
          -o jsonpath='{.status.channels[?(@.name=="stable")].currentCSVDesc.annotations.containerImage}')"
      2. Use the oc adm must-gather with the Custom Metrics Autoscaler Operator image:

        $ oc adm must-gather --image-stream=openshift/must-gather --image=${IMAGE}

    Example 3.1. Example must-gather output for the Custom Metric Autoscaler:

    └── openshift-keda
        ├── apps
        │   ├── daemonsets.yaml
        │   ├── deployments.yaml
        │   ├── replicasets.yaml
        │   └── statefulsets.yaml
        ├── apps.openshift.io
        │   └── deploymentconfigs.yaml
        ├── autoscaling
        │   └── horizontalpodautoscalers.yaml
        ├── batch
        │   ├── cronjobs.yaml
        │   └── jobs.yaml
        ├── build.openshift.io
        │   ├── buildconfigs.yaml
        │   └── builds.yaml
        ├── core
        │   ├── configmaps.yaml
        │   ├── endpoints.yaml
        │   ├── events.yaml
        │   ├── persistentvolumeclaims.yaml
        │   ├── pods.yaml
        │   ├── replicationcontrollers.yaml
        │   ├── secrets.yaml
        │   └── services.yaml
        ├── discovery.k8s.io
        │   └── endpointslices.yaml
        ├── image.openshift.io
        │   └── imagestreams.yaml
        ├── k8s.ovn.org
        │   ├── egressfirewalls.yaml
        │   └── egressqoses.yaml
        ├── keda.sh
        │   ├── kedacontrollers
        │   │   └── keda.yaml
        │   ├── scaledobjects
        │   │   └── example-scaledobject.yaml
        │   └── triggerauthentications
        │       └── example-triggerauthentication.yaml
        ├── monitoring.coreos.com
        │   └── servicemonitors.yaml
        ├── networking.k8s.io
        │   └── networkpolicies.yaml
        ├── openshift-keda.yaml
        ├── pods
        │   ├── custom-metrics-autoscaler-operator-58bd9f458-ptgwx
        │   │   ├── custom-metrics-autoscaler-operator
        │   │   │   └── custom-metrics-autoscaler-operator
        │   │   │       └── logs
        │   │   │           ├── current.log
        │   │   │           ├── previous.insecure.log
        │   │   │           └── previous.log
        │   │   └── custom-metrics-autoscaler-operator-58bd9f458-ptgwx.yaml
        │   ├── custom-metrics-autoscaler-operator-58bd9f458-thbsh
        │   │   └── custom-metrics-autoscaler-operator
        │   │       └── custom-metrics-autoscaler-operator
        │   │           └── logs
        │   ├── keda-metrics-apiserver-65c7cc44fd-6wq4g
        │   │   ├── keda-metrics-apiserver
        │   │   │   └── keda-metrics-apiserver
        │   │   │       └── logs
        │   │   │           ├── current.log
        │   │   │           ├── previous.insecure.log
        │   │   │           └── previous.log
        │   │   └── keda-metrics-apiserver-65c7cc44fd-6wq4g.yaml
        │   └── keda-operator-776cbb6768-fb6m5
        │       ├── keda-operator
        │       │   └── keda-operator
        │       │       └── logs
        │       │           ├── current.log
        │       │           ├── previous.insecure.log
        │       │           └── previous.log
        │       └── keda-operator-776cbb6768-fb6m5.yaml
        ├── policy
        │   └── poddisruptionbudgets.yaml
        └── route.openshift.io
            └── routes.yaml
  3. Create a compressed file from the must-gather directory that was created in your working directory. For example, on a computer that uses a Linux operating system, run the following command:

    $ tar cvaf must-gather.tar.gz must-gather.local.5421342344627712289/ 1
    1
    Replace must-gather-local.5421342344627712289/ with the actual directory name.
  4. Attach the compressed file to your support case on the Red Hat Customer Portal.

3.9. Viewing Operator metrics

The Custom Metrics Autoscaler Operator exposes ready-to-use metrics that it pulls from the on-cluster monitoring component. You can query the metrics by using the Prometheus Query Language (PromQL) to analyze and diagnose issues. All metrics are reset when the controller pod restarts.

3.9.1. Accessing performance metrics

You can access the metrics and run queries by using the OpenShift Container Platform web console.

Procedure

  1. Select the Administrator perspective in the OpenShift Container Platform web console.
  2. Select ObserveMetrics.
  3. To create a custom query, add your PromQL query to the Expression field.
  4. To add multiple queries, select Add Query.
3.9.1.1. Provided Operator metrics

The Custom Metrics Autoscaler Operator exposes the following metrics, which you can view by using the OpenShift Container Platform web console.

Table 3.1. Custom Metric Autoscaler Operator metrics
Metric nameDescription

keda_scaler_activity

Whether the particular scaler is active or inactive. A value of 1 indicates the scaler is active; a value of 0 indicates the scaler is inactive.

keda_scaler_metrics_value

The current value for each scaler’s metric, which is used by the Horizontal Pod Autoscaler (HPA) in computing the target average.

keda_scaler_metrics_latency

The latency of retrieving the current metric from each scaler.

keda_scaler_errors

The number of errors that have occurred for each scaler.

keda_scaler_errors_total

The total number of errors encountered for all scalers.

keda_scaled_object_errors

The number of errors that have occurred for each scaled obejct.

keda_resource_totals

The total number of Custom Metrics Autoscaler custom resources in each namespace for each custom resource type.

keda_trigger_totals

The total number of triggers by trigger type.

Custom Metrics Autoscaler Admission webhook metrics

The Custom Metrics Autoscaler Admission webhook also exposes the following Prometheus metrics.

Metric nameDescription

keda_scaled_object_validation_total

The number of scaled object validations.

keda_scaled_object_validation_errors

The number of validation errors.

3.10. Understanding how to add custom metrics autoscalers

To add a custom metrics autoscaler, create a ScaledObject custom resource for a deployment, stateful set, or custom resource. Create a ScaledJob custom resource for a job.

You can create only one scaled object for each workload that you want to scale. Also, you cannot use a scaled object and the horizontal pod autoscaler (HPA) on the same workload.

3.10.1. Adding a custom metrics autoscaler to a workload

You can create a custom metrics autoscaler for a workload that is created by a Deployment, StatefulSet, or custom resource object.

Prerequisites

  • The Custom Metrics Autoscaler Operator must be installed.
  • If you use a custom metrics autoscaler for scaling based on CPU or memory:

    • Your cluster administrator must have properly configured cluster metrics. You can use the oc describe PodMetrics <pod-name> command to determine if metrics are configured. If metrics are configured, the output appears similar to the following, with CPU and Memory displayed under Usage.

      $ oc describe PodMetrics openshift-kube-scheduler-ip-10-0-135-131.ec2.internal

      Example output

      Name:         openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
      Namespace:    openshift-kube-scheduler
      Labels:       <none>
      Annotations:  <none>
      API Version:  metrics.k8s.io/v1beta1
      Containers:
        Name:  wait-for-host-port
        Usage:
          Memory:  0
        Name:      scheduler
        Usage:
          Cpu:     8m
          Memory:  45440Ki
      Kind:        PodMetrics
      Metadata:
        Creation Timestamp:  2019-05-23T18:47:56Z
        Self Link:           /apis/metrics.k8s.io/v1beta1/namespaces/openshift-kube-scheduler/pods/openshift-kube-scheduler-ip-10-0-135-131.ec2.internal
      Timestamp:             2019-05-23T18:47:56Z
      Window:                1m0s
      Events:                <none>

    • The pods associated with the object you want to scale must include specified memory and CPU limits. For example:

      Example pod spec

      apiVersion: v1
      kind: Pod
      # ...
      spec:
        containers:
        - name: app
          image: images.my-company.example/app:v4
          resources:
            limits:
              memory: "128Mi"
              cpu: "500m"
      # ...

Procedure

  1. Create a YAML file similar to the following. Only the name <2>, object name <4>, and object kind <5> are required:

    Example scaled object

    apiVersion: keda.sh/v1alpha1
    kind: ScaledObject
    metadata:
      annotations:
        autoscaling.keda.sh/paused-replicas: "0" 1
      name: scaledobject 2
      namespace: my-namespace
    spec:
      scaleTargetRef:
        apiVersion: apps/v1 3
        name: example-deployment 4
        kind: Deployment 5
        envSourceContainerName: .spec.template.spec.containers[0] 6
      cooldownPeriod:  200 7
      maxReplicaCount: 100 8
      minReplicaCount: 0 9
      metricsServer: 10
        auditConfig:
          logFormat: "json"
          logOutputVolumeClaim: "persistentVolumeClaimName"
          policy:
            rules:
            - level: Metadata
            omitStages: "RequestReceived"
            omitManagedFields: false
          lifetime:
            maxAge: "2"
            maxBackup: "1"
            maxSize: "50"
      fallback: 11
        failureThreshold: 3
        replicas: 6
      pollingInterval: 30 12
      advanced:
        restoreToOriginalReplicaCount: false 13
        horizontalPodAutoscalerConfig:
          name: keda-hpa-scale-down 14
          behavior: 15
            scaleDown:
              stabilizationWindowSeconds: 300
              policies:
              - type: Percent
                value: 100
                periodSeconds: 15
      triggers:
      - type: prometheus 16
        metadata:
          serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
          namespace: kedatest
          metricName: http_requests_total
          threshold: '5'
          query: sum(rate(http_requests_total{job="test-app"}[1m]))
          authModes: basic
        authenticationRef: 17
          name: prom-triggerauthentication
          kind: TriggerAuthentication

    1
    Optional: Specifies that the Custom Metrics Autoscaler Operator is to scale the replicas to the specified value and stop autoscaling, as described in the "Pausing the custom metrics autoscaler for a workload" section.
    2
    Specifies a name for this custom metrics autoscaler.
    3
    Optional: Specifies the API version of the target resource. The default is apps/v1.
    4
    Specifies the name of the object that you want to scale.
    5
    Specifies the kind as Deployment, StatefulSet or CustomResource.
    6
    Optional: Specifies the name of the container in the target resource, from which the custom metrics autoscaler gets environment variables holding secrets and so forth. The default is .spec.template.spec.containers[0].
    7
    Optional. Specifies the period in seconds to wait after the last trigger is reported before scaling the deployment back to 0 if the minReplicaCount is set to 0. The default is 300.
    8
    Optional: Specifies the maximum number of replicas when scaling up. The default is 100.
    9
    Optional: Specifies the minimum number of replicas when scaling down.
    10
    Optional: Specifies the parameters for audit logs. as described in the "Configuring audit logging" section.
    11
    Optional: Specifies the number of replicas to fall back to if a scaler fails to get metrics from the source for the number of times defined by the failureThreshold parameter. For more information on fallback behavior, see the KEDA documentation.
    12
    Optional: Specifies the interval in seconds to check each trigger on. The default is 30.
    13
    Optional: Specifies whether to scale back the target resource to the original replica count after the scaled object is deleted. The default is false, which keeps the replica count as it is when the scaled object is deleted.
    14
    Optional: Specifies a name for the horizontal pod autoscaler. The default is keda-hpa-{scaled-object-name}.
    15
    Optional: Specifies a scaling policy to use to control the rate to scale pods up or down, as described in the "Scaling policies" section.
    16
    Specifies the trigger to use as the basis for scaling, as described in the "Understanding the custom metrics autoscaler triggers" section. This example uses OpenShift Container Platform monitoring.
    17
    Optional: Specifies a trigger authentication or a cluster trigger authentication. For more information, see Understanding the custom metrics autoscaler trigger authentication in the Additional resources section.
    • Enter TriggerAuthentication to use a trigger authentication. This is the default.
    • Enter ClusterTriggerAuthentication to use a cluster trigger authentication.
  2. Create the custom metrics autoscaler by running the following command:

    $ oc create -f <filename>.yaml

Verification

  • View the command output to verify that the custom metrics autoscaler was created:

    $ oc get scaledobject <scaled_object_name>

    Example output

    NAME            SCALETARGETKIND      SCALETARGETNAME        MIN   MAX   TRIGGERS     AUTHENTICATION               READY   ACTIVE   FALLBACK   AGE
    scaledobject    apps/v1.Deployment   example-deployment     0     50    prometheus   prom-triggerauthentication   True    True     True       17s

    Note the following fields in the output:

    • TRIGGERS: Indicates the trigger, or scaler, that is being used.
    • AUTHENTICATION: Indicates the name of any trigger authentication being used.
    • READY: Indicates whether the scaled object is ready to start scaling:

      • If True, the scaled object is ready.
      • If False, the scaled object is not ready because of a problem in one or more of the objects you created.
    • ACTIVE: Indicates whether scaling is taking place:

      • If True, scaling is taking place.
      • If False, scaling is not taking place because there are no metrics or there is a problem in one or more of the objects you created.
    • FALLBACK: Indicates whether the custom metrics autoscaler is able to get metrics from the source

      • If False, the custom metrics autoscaler is getting metrics.
      • If True, the custom metrics autoscaler is getting metrics because there are no metrics or there is a problem in one or more of the objects you created.

3.10.2. Adding a custom metrics autoscaler to a job

You can create a custom metrics autoscaler for any Job object.

Important

Scaling by using a scaled job is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

Prerequisites

  • The Custom Metrics Autoscaler Operator must be installed.

Procedure

  1. Create a YAML file similar to the following:

    kind: ScaledJob
    apiVersion: keda.sh/v1alpha1
    metadata:
      name: scaledjob
      namespace: my-namespace
    spec:
      failedJobsHistoryLimit: 5
      jobTargetRef:
        activeDeadlineSeconds: 600 1
        backoffLimit: 6 2
        parallelism: 1 3
        completions: 1 4
        template:  5
          metadata:
            name: pi
          spec:
            containers:
            - name: pi
              image: perl
              command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      maxReplicaCount: 100 6
      pollingInterval: 30 7
      successfulJobsHistoryLimit: 5 8
      failedJobsHistoryLimit: 5 9
      envSourceContainerName: 10
      rolloutStrategy: gradual 11
      scalingStrategy: 12
        strategy: "custom"
        customScalingQueueLengthDeduction: 1
        customScalingRunningJobPercentage: "0.5"
        pendingPodConditions:
          - "Ready"
          - "PodScheduled"
          - "AnyOtherCustomPodCondition"
        multipleScalersCalculation : "max"
      triggers:
      - type: prometheus 13
        metadata:
          serverAddress: https://thanos-querier.openshift-monitoring.svc.cluster.local:9092
          namespace: kedatest
          metricName: http_requests_total
          threshold: '5'
          query: sum(rate(http_requests_total{job="test-app"}[1m]))
          authModes: "bearer"
        authenticationRef: 14
          name: prom-cluster-triggerauthentication
    1
    Specifies the maximum duration the job can run.
    2
    Specifies the number of retries for a job. The default is 6.
    3
    Optional: Specifies how many pod replicas a job should run in parallel; defaults to 1.
    • For non-parallel jobs, leave unset. When unset, the default is 1.
    4
    Optional: Specifies how many successful pod completions are needed to mark a job completed.
    • For non-parallel jobs, leave unset. When unset, the default is 1.
    • For parallel jobs with a fixed completion count, specify the number of completions.
    • For parallel jobs with a work queue, leave unset. When unset the default is the value of the parallelism parameter.
    5
    Specifies the template for the pod the controller creates.
    6
    Optional: Specifies the maximum number of replicas when scaling up. The default is 100.
    7
    Optional: Specifies the interval in seconds to check each trigger on. The default is 30.
    8
    Optional: Specifies the number of successful finished jobs should be kept. The default is 100.
    9
    Optional: Specifies how many failed jobs should be kept. The default is 100.
    10
    Optional: Specifies the name of the container in the target resource, from which the custom autoscaler gets environment variables holding secrets and so forth. The default is .spec.template.spec.containers[0].
    11
    Optional: Specifies whether existing jobs are terminated whenever a scaled job is being updated:
    • default: The autoscaler terminates an existing job if its associated scaled job is updated. The autoscaler recreates the job with the latest specs.
    • gradual: The autoscaler does not terminate an existing job if its associated scaled job is updated. The autoscaler creates new jobs with the latest specs.
    12
    Optional: Specifies a scaling strategy: default, custom, or accurate. The default is default. For more information, see the link in the "Additional resources" section that follows.
    13
    Specifies the trigger to use as the basis for scaling, as described in the "Understanding the custom metrics autoscaler triggers" section.
    14
    Optional: Specifies a trigger authentication or a cluster trigger authentication. For more information, see Understanding the custom metrics autoscaler trigger authentication in the Additional resources section.
    • Enter TriggerAuthentication to use a trigger authentication. This is the default.
    • Enter ClusterTriggerAuthentication to use a cluster trigger authentication.
  2. Create the custom metrics autoscaler by running the following command:

    $ oc create -f <filename>.yaml

Verification

  • View the command output to verify that the custom metrics autoscaler was created:

    $ oc get scaledjob <scaled_job_name>

    Example output

    NAME        MAX   TRIGGERS     AUTHENTICATION              READY   ACTIVE    AGE
    scaledjob   100   prometheus   prom-triggerauthentication  True    True      8s

    Note the following fields in the output:

    • TRIGGERS: Indicates the trigger, or scaler, that is being used.
    • AUTHENTICATION: Indicates the name of any trigger authentication being used.
    • READY: Indicates whether the scaled object is ready to start scaling:

      • If True, the scaled object is ready.
      • If False, the scaled object is not ready because of a problem in one or more of the objects you created.
    • ACTIVE: Indicates whether scaling is taking place:

      • If True, scaling is taking place.
      • If False, scaling is not taking place because there are no metrics or there is a problem in one or more of the objects you created.

3.10.3. Additional resources

3.11. Removing the Custom Metrics Autoscaler Operator

You can remove the custom metrics autoscaler from your OpenShift Container Platform cluster. After removing the Custom Metrics Autoscaler Operator, remove other components associated with the Operator to avoid potential issues.

Note

Delete the KedaController custom resource (CR) first. If you do not delete the KedaController CR, OpenShift Container Platform can hang when you delete the openshift-keda project. If you delete the Custom Metrics Autoscaler Operator before deleting the CR, you are not able to delete the CR.

3.11.1. Uninstalling the Custom Metrics Autoscaler Operator

Use the following procedure to remove the custom metrics autoscaler from your OpenShift Container Platform cluster.

Prerequisites

  • The Custom Metrics Autoscaler Operator must be installed.

Procedure

  1. In the OpenShift Container Platform web console, click OperatorsInstalled Operators.
  2. Switch to the openshift-keda project.
  3. Remove the KedaController custom resource.

    1. Find the CustomMetricsAutoscaler Operator and click the KedaController tab.
    2. Find the custom resource, and then click Delete KedaController.
    3. Click Uninstall.
  4. Remove the Custom Metrics Autoscaler Operator:

    1. Click OperatorsInstalled Operators.
    2. Find the CustomMetricsAutoscaler Operator and click the Options menu kebab and select Uninstall Operator.
    3. Click Uninstall.
  5. Optional: Use the OpenShift CLI to remove the custom metrics autoscaler components:

    1. Delete the custom metrics autoscaler CRDs:

      • clustertriggerauthentications.keda.sh
      • kedacontrollers.keda.sh
      • scaledjobs.keda.sh
      • scaledobjects.keda.sh
      • triggerauthentications.keda.sh
      $ oc delete crd clustertriggerauthentications.keda.sh kedacontrollers.keda.sh scaledjobs.keda.sh scaledobjects.keda.sh triggerauthentications.keda.sh

      Deleting the CRDs removes the associated roles, cluster roles, and role bindings. However, there might be a few cluster roles that must be manually deleted.

    2. List any custom metrics autoscaler cluster roles:

      $ oc get clusterrole | grep keda.sh
    3. Delete the listed custom metrics autoscaler cluster roles. For example:

      $ oc delete clusterrole.keda.sh-v1alpha1-admin
    4. List any custom metrics autoscaler cluster role bindings:

      $ oc get clusterrolebinding | grep keda.sh
    5. Delete the listed custom metrics autoscaler cluster role bindings. For example:

      $ oc delete clusterrolebinding.keda.sh-v1alpha1-admin
  6. Delete the custom metrics autoscaler project:

    $ oc delete project openshift-keda
  7. Delete the Cluster Metric Autoscaler Operator:

    $ oc delete operator/openshift-custom-metrics-autoscaler-operator.openshift-keda

Chapter 4. Controlling pod placement onto nodes (scheduling)

4.1. Controlling pod placement using the scheduler

Pod scheduling is an internal process that determines placement of new pods onto nodes within the cluster.

The scheduler code has a clean separation that watches new pods as they get created and identifies the most suitable node to host them. It then creates bindings (pod to node bindings) for the pods using the master API.

Default pod scheduling
OpenShift Container Platform comes with a default scheduler that serves the needs of most users. The default scheduler uses both inherent and customization tools to determine the best fit for a pod.
Advanced pod scheduling

In situations where you might want more control over where new pods are placed, the OpenShift Container Platform advanced scheduling features allow you to configure a pod so that the pod is required or has a preference to run on a particular node or alongside a specific pod.

You can control pod placement by using the following scheduling features:

4.1.1. About the default scheduler

The default OpenShift Container Platform pod scheduler is responsible for determining the placement of new pods onto nodes within the cluster. It reads data from the pod and finds a node that is a good fit based on configured profiles. It is completely independent and exists as a standalone solution. It does not modify the pod; it creates a binding for the pod that ties the pod to the particular node.

4.1.1.1. Understanding default scheduling

The existing generic scheduler is the default platform-provided scheduler engine that selects a node to host the pod in a three-step operation:

Filters the nodes
The available nodes are filtered based on the constraints or requirements specified. This is done by running each node through the list of filter functions called predicates, or filters.
Prioritizes the filtered list of nodes
This is achieved by passing each node through a series of priority, or scoring, functions that assign it a score between 0 - 10, with 0 indicating a bad fit and 10 indicating a good fit to host the pod. The scheduler configuration can also take in a simple weight (positive numeric value) for each scoring function. The node score provided by each scoring function is multiplied by the weight (default weight for most scores is 1) and then combined by adding the scores for each node provided by all the scores. This weight attribute can be used by administrators to give higher importance to some scores.
Selects the best fit node
The nodes are sorted based on their scores and the node with the highest score is selected to host the pod. If multiple nodes have the same high score, then one of them is selected at random.

4.1.2. Scheduler use cases

One of the important use cases for scheduling within OpenShift Container Platform is to support flexible affinity and anti-affinity policies.

4.1.2.1. Infrastructure topological levels

Administrators can define multiple topological levels for their infrastructure (nodes) by specifying labels on nodes. For example: region=r1, zone=z1, rack=s1.

These label names have no particular meaning and administrators are free to name their infrastructure levels anything, such as city/building/room. Also, administrators can define any number of levels for their infrastructure topology, with three levels usually being adequate (such as: regionszonesracks). Administrators can specify affinity and anti-affinity rules at each of these levels in any combination.

4.1.2.2. Affinity

Administrators should be able to configure the scheduler to specify affinity at any topological level, or even at multiple levels. Affinity at a particular level indicates that all pods that belong to the same service are scheduled onto nodes that belong to the same level. This handles any latency requirements of applications by allowing administrators to ensure that peer pods do not end up being too geographically separated. If no node is available within the same affinity group to host the pod, then the pod is not scheduled.

If you need greater control over where the pods are scheduled, see Controlling pod placement on nodes using node affinity rules and Placing pods relative to other pods using affinity and anti-affinity rules.

These advanced scheduling features allow administrators to specify which node a pod can be scheduled on and to force or reject scheduling relative to other pods.

4.1.2.3. Anti-affinity

Administrators should be able to configure the scheduler to specify anti-affinity at any topological level, or even at multiple levels. Anti-affinity (or 'spread') at a particular level indicates that all pods that belong to the same service are spread across nodes that belong to that level. This ensures that the application is well spread for high availability purposes. The scheduler tries to balance the service pods across all applicable nodes as evenly as possible.

If you need greater control over where the pods are scheduled, see Controlling pod placement on nodes using node affinity rules and Placing pods relative to other pods using affinity and anti-affinity rules.

These advanced scheduling features allow administrators to specify which node a pod can be scheduled on and to force or reject scheduling relative to other pods.

4.2. Scheduling pods using a scheduler profile

You can configure OpenShift Container Platform to use a scheduling profile to schedule pods onto nodes within the cluster.

4.2.1. About scheduler profiles

You can specify a scheduler profile to control how pods are scheduled onto nodes.

The following scheduler profiles are available:

LowNodeUtilization
This profile attempts to spread pods evenly across nodes to get low resource usage per node. This profile provides the default scheduler behavior.
HighNodeUtilization
This profile attempts to place as many pods as possible on to as few nodes as possible. This minimizes node count and has high resource usage per node.
NoScoring
This is a low-latency profile that strives for the quickest scheduling cycle by disabling all score plugins. This might sacrifice better scheduling decisions for faster ones.

4.2.2. Configuring a scheduler profile

You can configure the scheduler to use a scheduler profile.

Prerequisites

  • Access to the cluster as a user with the cluster-admin role.

Procedure

  1. Edit the Scheduler object:

    $ oc edit scheduler cluster
  2. Specify the profile to use in the spec.profile field:

    apiVersion: config.openshift.io/v1
    kind: Scheduler
    metadata:
      name: cluster
    #...
    spec:
      mastersSchedulable: false
      profile: HighNodeUtilization 1
    #...
    1
    Set to LowNodeUtilization, HighNodeUtilization, or NoScoring.
  3. Save the file to apply the changes.

4.3. Placing pods relative to other pods using affinity and anti-affinity rules

Affinity is a property of pods that controls the nodes on which they prefer to be scheduled. Anti-affinity is a property of pods that prevents a pod from being scheduled on a node.

In OpenShift Container Platform, pod affinity and pod anti-affinity allow you to constrain which nodes your pod is eligible to be scheduled on based on the key-value labels on other pods.

4.3.1. Understanding pod affinity

Pod affinity and pod anti-affinity allow you to constrain which nodes your pod is eligible to be scheduled on based on the key/value labels on other pods.

  • Pod affinity can tell the scheduler to locate a new pod on the same node as other pods if the label selector on the new pod matches the label on the current pod.
  • Pod anti-affinity can prevent the scheduler from locating a new pod on the same node as pods with the same labels if the label selector on the new pod matches the label on the current pod.

For example, using affinity rules, you could spread or pack pods within a service or relative to pods in other services. Anti-affinity rules allow you to prevent pods of a particular service from scheduling on the same nodes as pods of another service that are known to interfere with the performance of the pods of the first service. Or, you could spread the pods of a service across nodes, availability zones, or availability sets to reduce correlated failures.

Note

A label selector might match pods with multiple pod deployments. Use unique combinations of labels when configuring anti-affinity rules to avoid matching pods.

There are two types of pod affinity rules: required and preferred.

Required rules must be met before a pod can be scheduled on a node. Preferred rules specify that, if the rule is met, the scheduler tries to enforce the rules, but does not guarantee enforcement.

Note

Depending on your pod priority and preemption settings, the scheduler might not be able to find an appropriate node for a pod without violating affinity requirements. If so, a pod might not be scheduled.

To prevent this situation, carefully configure pod affinity with equal-priority pods.

You configure pod affinity/anti-affinity through the Pod spec files. You can specify a required rule, a preferred rule, or both. If you specify both, the node must first meet the required rule, then attempts to meet the preferred rule.

The following example shows a Pod spec configured for pod affinity and anti-affinity.

In this example, the pod affinity rule indicates that the pod can schedule onto a node only if that node has at least one already-running pod with a label that has the key security and value S1. The pod anti-affinity rule says that the pod prefers to not schedule onto a node if that node is already running a pod with label having key security and value S2.

Sample Pod config file with pod affinity

apiVersion: v1
kind: Pod
metadata:
  name: with-pod-affinity
spec:
  affinity:
    podAffinity: 1
      requiredDuringSchedulingIgnoredDuringExecution: 2
      - labelSelector:
          matchExpressions:
          - key: security 3
            operator: In 4
            values:
            - S1 5
        topologyKey: failure-domain.beta.kubernetes.io/zone
  containers:
  - name: with-pod-affinity
    image: docker.io/ocpqe/hello-pod

1
Stanza to configure pod affinity.
2
Defines a required rule.
3 5
The key and value (label) that must be matched to apply the rule.
4
The operator represents the relationship between the label on the existing pod and the set of values in the matchExpression parameters in the specification for the new pod. Can be In, NotIn, Exists, or DoesNotExist.

Sample Pod config file with pod anti-affinity

apiVersion: v1
kind: Pod
metadata:
  name: with-pod-antiaffinity
spec:
  affinity:
    podAntiAffinity: 1
      preferredDuringSchedulingIgnoredDuringExecution: 2
      - weight: 100  3
        podAffinityTerm:
          labelSelector:
            matchExpressions:
            - key: security 4
              operator: In 5
              values:
              - S2
          topologyKey: kubernetes.io/hostname
  containers:
  - name: with-pod-affinity
    image: docker.io/ocpqe/hello-pod

1
Stanza to configure pod anti-affinity.
2
Defines a preferred rule.
3
Specifies a weight for a preferred rule. The node with the highest weight is preferred.
4
Description of the pod label that determines when the anti-affinity rule applies. Specify a key and value for the label.
5
The operator represents the relationship between the label on the existing pod and the set of values in the matchExpression parameters in the specification for the new pod. Can be In, NotIn, Exists, or DoesNotExist.
Note

If labels on a node change at runtime such that the affinity rules on a pod are no longer met, the pod continues to run on the node.

4.3.2. Configuring a pod affinity rule

The following steps demonstrate a simple two-pod configuration that creates pod with a label and a pod that uses affinity to allow scheduling with that pod.

Note

You cannot add an affinity directly to a scheduled pod.

Procedure

  1. Create a pod with a specific label in the pod spec:

    1. Create a YAML file with the following content:

      apiVersion: v1
      kind: Pod
      metadata:
        name: security-s1
        labels:
          security: S1
      spec:
        containers:
        - name: security-s1
          image: docker.io/ocpqe/hello-pod
    2. Create the pod.

      $ oc create -f <pod-spec>.yaml
  2. When creating other pods, configure the following parameters to add the affinity:

    1. Create a YAML file with the following content:

      apiVersion: v1
      kind: Pod
      metadata:
        name: security-s1-east
      #...
      spec
        affinity 1
          podAffinity:
            requiredDuringSchedulingIgnoredDuringExecution: 2
            - labelSelector:
                matchExpressions:
                - key: security 3
                  values:
                  - S1
                  operator: In 4
              topologyKey: topology.kubernetes.io/zone 5
      #...
      1
      Adds a pod affinity.
      2
      Configures the requiredDuringSchedulingIgnoredDuringExecution parameter or the preferredDuringSchedulingIgnoredDuringExecution parameter.
      3
      Specifies the key and values that must be met. If you want the new pod to be scheduled with the other pod, use the same key and values parameters as the label on the first pod.
      4
      Specifies an operator. The operator can be In, NotIn, Exists, or DoesNotExist. For example, use the operator In to require the label to be in the node.
      5
      Specify a topologyKey, which is a prepopulated Kubernetes label that the system uses to denote such a topology domain.
    2. Create the pod.

      $ oc create -f <pod-spec>.yaml

4.3.3. Configuring a pod anti-affinity rule

The following steps demonstrate a simple two-pod configuration that creates pod with a label and a pod that uses an anti-affinity preferred rule to attempt to prevent scheduling with that pod.

Note

You cannot add an affinity directly to a scheduled pod.

Procedure

  1. Create a pod with a specific label in the pod spec:

    1. Create a YAML file with the following content:

      apiVersion: v1
      kind: Pod
      metadata:
        name: security-s1
        labels:
          security: S1
      spec:
        containers:
        - name: security-s1
          image: docker.io/ocpqe/hello-pod
    2. Create the pod.

      $ oc create -f <pod-spec>.yaml
  2. When creating other pods, configure the following parameters:

    1. Create a YAML file with the following content:

      apiVersion: v1
      kind: Pod
      metadata:
        name: security-s2-east
      #...
      spec
        affinity 1
          podAntiAffinity:
            preferredDuringSchedulingIgnoredDuringExecution: 2
            - weight: 100 3
              podAffinityTerm:
                labelSelector:
                  matchExpressions:
                  - key: security 4
                    values:
                    - S1
                    operator: In 5
                topologyKey: kubernetes.io/hostname 6
      #...
      1
      Adds a pod anti-affinity.
      2
      Configures the requiredDuringSchedulingIgnoredDuringExecution parameter or the preferredDuringSchedulingIgnoredDuringExecution parameter.
      3
      For a preferred rule, specifies a weight for the node, 1-100. The node that with highest weight is preferred.
      4
      Specifies the key and values that must be met. If you want the new pod to not be scheduled with the other pod, use the same key and values parameters as the label on the first pod.
      5
      Specifies an operator. The operator can be In, NotIn, Exists, or DoesNotExist. For example, use the operator In to require the label to be in the node.
      6
      Specifies a topologyKey, which is a prepopulated Kubernetes label that the system uses to denote such a topology domain.
    2. Create the pod.

      $ oc create -f <pod-spec>.yaml

4.3.4. Sample pod affinity and anti-affinity rules

The following examples demonstrate pod affinity and pod anti-affinity.

4.3.4.1. Pod Affinity

The following example demonstrates pod affinity for pods with matching labels and label selectors.

  • The pod team4 has the label team:4.

    apiVersion: v1
    kind: Pod
    metadata:
      name: team4
      labels:
         team: "4"
    #...
    spec:
      containers:
      - name: ocp
        image: docker.io/ocpqe/hello-pod
    #...
  • The pod team4a has the label selector team:4 under podAffinity.

    apiVersion: v1
    kind: Pod
    metadata:
      name: team4a
    #...
    spec:
      affinity:
        podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: team
                operator: In
                values:
                - "4"
            topologyKey: kubernetes.io/hostname
      containers:
      - name: pod-affinity
        image: docker.io/ocpqe/hello-pod
    #...
  • The team4a pod is scheduled on the same node as the team4 pod.
4.3.4.2. Pod Anti-affinity

The following example demonstrates pod anti-affinity for pods with matching labels and label selectors.

  • The pod pod-s1 has the label security:s1.

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s1
      labels:
        security: s1
    #...
    spec:
      containers:
      - name: ocp
        image: docker.io/ocpqe/hello-pod
    #...
  • The pod pod-s2 has the label selector security:s1 under podAntiAffinity.

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s2
    #...
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: security
                operator: In
                values:
                - s1
            topologyKey: kubernetes.io/hostname
      containers:
      - name: pod-antiaffinity
        image: docker.io/ocpqe/hello-pod
    #...
  • The pod pod-s2 cannot be scheduled on the same node as pod-s1.
4.3.4.3. Pod Affinity with no Matching Labels

The following example demonstrates pod affinity for pods without matching labels and label selectors.

  • The pod pod-s1 has the label security:s1.

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s1
      labels:
        security: s1
    #...
    spec:
      containers:
      - name: ocp
        image: docker.io/ocpqe/hello-pod
    #...
  • The pod pod-s2 has the label selector security:s2.

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s2
    #...
    spec:
      affinity:
        podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: security
                operator: In
                values:
                - s2
            topologyKey: kubernetes.io/hostname
      containers:
      - name: pod-affinity
        image: docker.io/ocpqe/hello-pod
    #...
  • The pod pod-s2 is not scheduled unless there is a node with a pod that has the security:s2 label. If there is no other pod with that label, the new pod remains in a pending state:

    Example output

    NAME      READY     STATUS    RESTARTS   AGE       IP        NODE
    pod-s2    0/1       Pending   0          32s       <none>

4.3.5. Using pod affinity and anti-affinity to control where an Operator is installed

By default, when you install an Operator, OpenShift Container Platform installs the Operator pod to one of your worker nodes randomly. However, there might be situations where you want that pod scheduled on a specific node or set of nodes.

The following examples describe situations where you might want to schedule an Operator pod to a specific node or set of nodes:

  • If an Operator requires a particular platform, such as amd64 or arm64
  • If an Operator requires a particular operating system, such as Linux or Windows
  • If you want Operators that work together scheduled on the same host or on hosts located on the same rack
  • If you want Operators dispersed throughout the infrastructure to avoid downtime due to network or hardware issues

You can control where an Operator pod is installed by adding a pod affinity or anti-affinity to the Operator’s Subscription object.

The following example shows how to use pod anti-affinity to prevent the installation the Custom Metrics Autoscaler Operator from any node that has pods with a specific label:

Pod affinity example that places the Operator pod on one or more specific nodes

apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-custom-metrics-autoscaler-operator
  namespace: openshift-keda
spec:
  name: my-package
  source: my-operators
  sourceNamespace: operator-registries
  config:
    affinity:
      podAffinity: 1
        requiredDuringSchedulingIgnoredDuringExecution:
        - labelSelector:
            matchExpressions:
            - key: app
              operator: In
              values:
              - test
          topologyKey: kubernetes.io/hostname
#...

1
A pod affinity that places the Operator’s pod on a node that has pods with the app=test label.

Pod anti-affinity example that prevents the Operator pod from one or more specific nodes

apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-custom-metrics-autoscaler-operator
  namespace: openshift-keda
spec:
  name: my-package
  source: my-operators
  sourceNamespace: operator-registries
  config:
    affinity:
      podAntiAffinity: 1
        requiredDuringSchedulingIgnoredDuringExecution:
        - labelSelector:
            matchExpressions:
            - key: cpu
              operator: In
              values:
              - high
          topologyKey: kubernetes.io/hostname
#...

1
A pod anti-affinity that prevents the Operator’s pod from being scheduled on a node that has pods with the cpu=high label.

Procedure

To control the placement of an Operator pod, complete the following steps:

  1. Install the Operator as usual.
  2. If needed, ensure that your nodes are labeled to properly respond to the affinity.
  3. Edit the Operator Subscription object to add an affinity:
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-custom-metrics-autoscaler-operator
  namespace: openshift-keda
spec:
  name: my-package
  source: my-operators
  sourceNamespace: operator-registries
  config:
    affinity:
      podAntiAffinity: 1
        requiredDuringSchedulingIgnoredDuringExecution:
          podAffinityTerm:
            labelSelector:
              matchExpressions:
              - key: kubernetes.io/hostname
                operator: In
                values:
                - ip-10-0-185-229.ec2.internal
            topologyKey: topology.kubernetes.io/zone
#...
1
Add a podAffinity or podAntiAffinity.

Verification

  • To ensure that the pod is deployed on the specific node, run the following command:

    $ oc get pods -o wide

    Example output

    NAME                                                  READY   STATUS    RESTARTS   AGE   IP            NODE                           NOMINATED NODE   READINESS GATES
    custom-metrics-autoscaler-operator-5dcc45d656-bhshg   1/1     Running   0          50s   10.131.0.20   ip-10-0-185-229.ec2.internal   <none>           <none>

4.4. Controlling pod placement on nodes using node affinity rules

Affinity is a property of pods that controls the nodes on which they prefer to be scheduled.

In OpenShift Container Platform node affinity is a set of rules used by the scheduler to determine where a pod can be placed. The rules are defined using custom labels on the nodes and label selectors specified in pods.

4.4.1. Understanding node affinity

Node affinity allows a pod to specify an affinity towards a group of nodes it can be placed on. The node does not have control over the placement.

For example, you could configure a pod to only run on a node with a specific CPU or in a specific availability zone.

There are two types of node affinity rules: required and preferred.

Required rules must be met before a pod can be scheduled on a node. Preferred rules specify that, if the rule is met, the scheduler tries to enforce the rules, but does not guarantee enforcement.

Note

If labels on a node change at runtime that results in an node affinity rule on a pod no longer being met, the pod continues to run on the node.

You configure node affinity through the Pod spec file. You can specify a required rule, a preferred rule, or both. If you specify both, the node must first meet the required rule, then attempts to meet the preferred rule.

The following example is a Pod spec with a rule that requires the pod be placed on a node with a label whose key is e2e-az-NorthSouth and whose value is either e2e-az-North or e2e-az-South:

Example pod configuration file with a node affinity required rule

apiVersion: v1
kind: Pod
metadata:
  name: with-node-affinity
spec:
  affinity:
    nodeAffinity: 1
      requiredDuringSchedulingIgnoredDuringExecution: 2
        nodeSelectorTerms:
        - matchExpressions:
          - key: e2e-az-NorthSouth 3
            operator: In 4
            values:
            - e2e-az-North 5
            - e2e-az-South 6
  containers:
  - name: with-node-affinity
    image: docker.io/ocpqe/hello-pod
#...

1
The stanza to configure node affinity.
2
Defines a required rule.
3 5 6
The key/value pair (label) that must be matched to apply the rule.
4
The operator represents the relationship between the label on the node and the set of values in the matchExpression parameters in the Pod spec. This value can be In, NotIn, Exists, or DoesNotExist, Lt, or Gt.

The following example is a node specification with a preferred rule that a node with a label whose key is e2e-az-EastWest and whose value is either e2e-az-East or e2e-az-West is preferred for the pod:

Example pod configuration file with a node affinity preferred rule

apiVersion: v1
kind: Pod
metadata:
  name: with-node-affinity
spec:
  affinity:
    nodeAffinity: 1
      preferredDuringSchedulingIgnoredDuringExecution: 2
      - weight: 1 3
        preference:
          matchExpressions:
          - key: e2e-az-EastWest 4
            operator: In 5
            values:
            - e2e-az-East 6
            - e2e-az-West 7
  containers:
  - name: with-node-affinity
    image: docker.io/ocpqe/hello-pod
#...

1
The stanza to configure node affinity.
2
Defines a preferred rule.
3
Specifies a weight for a preferred rule. The node with highest weight is preferred.
4 6 7
The key/value pair (label) that must be matched to apply the rule.
5
The operator represents the relationship between the label on the node and the set of values in the matchExpression parameters in the Pod spec. This value can be In, NotIn, Exists, or DoesNotExist, Lt, or Gt.

There is no explicit node anti-affinity concept, but using the NotIn or DoesNotExist operator replicates that behavior.

Note

If you are using node affinity and node selectors in the same pod configuration, note the following:

  • If you configure both nodeSelector and nodeAffinity, both conditions must be satisfied for the pod to be scheduled onto a candidate node.
  • If you specify multiple nodeSelectorTerms associated with nodeAffinity types, then the pod can be scheduled onto a node if one of the nodeSelectorTerms is satisfied.
  • If you specify multiple matchExpressions associated with nodeSelectorTerms, then the pod can be scheduled onto a node only if all matchExpressions are satisfied.

4.4.2. Configuring a required node affinity rule

Required rules must be met before a pod can be scheduled on a node.

Procedure

The following steps demonstrate a simple configuration that creates a node and a pod that the scheduler is required to place on the node.

  1. Add a label to a node using the oc label node command:

    $ oc label node node1 e2e-az-name=e2e-az1
    Tip

    You can alternatively apply the following YAML to add the label:

    kind: Node
    apiVersion: v1
    metadata:
      name: <node_name>
      labels:
        e2e-az-name: e2e-az1
    #...
  2. Create a pod with a specific label in the pod spec:

    1. Create a YAML file with the following content:

      Note

      You cannot add an affinity directly to a scheduled pod.

      Example output

      apiVersion: v1
      kind: Pod
      metadata:
        name: s1
      spec:
        affinity: 1
          nodeAffinity:
            requiredDuringSchedulingIgnoredDuringExecution: 2
              nodeSelectorTerms:
              - matchExpressions:
                - key: e2e-az-name 3
                  values:
                  - e2e-az1
                  - e2e-az2
                  operator: In 4
      #...

      1
      Adds a pod affinity.
      2
      Configures the requiredDuringSchedulingIgnoredDuringExecution parameter.
      3
      Specifies the key and values that must be met. If you want the new pod to be scheduled on the node you edited, use the same key and values parameters as the label in the node.
      4
      Specifies an operator. The operator can be In, NotIn, Exists, or DoesNotExist. For example, use the operator In to require the label to be in the node.
    2. Create the pod:

      $ oc create -f <file-name>.yaml

4.4.3. Configuring a preferred node affinity rule

Preferred rules specify that, if the rule is met, the scheduler tries to enforce the rules, but does not guarantee enforcement.

Procedure

The following steps demonstrate a simple configuration that creates a node and a pod that the scheduler tries to place on the node.

  1. Add a label to a node using the oc label node command:

    $ oc label node node1 e2e-az-name=e2e-az3
  2. Create a pod with a specific label:

    1. Create a YAML file with the following content:

      Note

      You cannot add an affinity directly to a scheduled pod.

      apiVersion: v1
      kind: Pod
      metadata:
        name: s1
      spec:
        affinity: 1
          nodeAffinity:
            preferredDuringSchedulingIgnoredDuringExecution: 2
            - weight: 3
              preference:
                matchExpressions:
                - key: e2e-az-name 4
                  values:
                  - e2e-az3
                  operator: In 5
      #...
      1
      Adds a pod affinity.
      2
      Configures the preferredDuringSchedulingIgnoredDuringExecution parameter.
      3
      Specifies a weight for the node, as a number 1-100. The node with highest weight is preferred.
      4
      Specifies the key and values that must be met. If you want the new pod to be scheduled on the node you edited, use the same key and values parameters as the label in the node.
      5
      Specifies an operator. The operator can be In, NotIn, Exists, or DoesNotExist. For example, use the operator In to require the label to be in the node.
    2. Create the pod.

      $ oc create -f <file-name>.yaml

4.4.4. Sample node affinity rules

The following examples demonstrate node affinity.

4.4.4.1. Node affinity with matching labels

The following example demonstrates node affinity for a node and pod with matching labels:

  • The Node1 node has the label zone:us:

    $ oc label node node1 zone=us
    Tip

    You can alternatively apply the following YAML to add the label:

    kind: Node
    apiVersion: v1
    metadata:
      name: <node_name>
      labels:
        zone: us
    #...
  • The pod-s1 pod has the zone and us key/value pair under a required node affinity rule:

    $ cat pod-s1.yaml

    Example output

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s1
    spec:
      containers:
        - image: "docker.io/ocpqe/hello-pod"
          name: hello-pod
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                - key: "zone"
                  operator: In
                  values:
                  - us
    #...

  • The pod-s1 pod can be scheduled on Node1:

    $ oc get pod -o wide

    Example output

    NAME     READY     STATUS       RESTARTS   AGE      IP      NODE
    pod-s1   1/1       Running      0          4m       IP1     node1

4.4.4.2. Node affinity with no matching labels

The following example demonstrates node affinity for a node and pod without matching labels:

  • The Node1 node has the label zone:emea:

    $ oc label node node1 zone=emea
    Tip

    You can alternatively apply the following YAML to add the label:

    kind: Node
    apiVersion: v1
    metadata:
      name: <node_name>
      labels:
        zone: emea
    #...
  • The pod-s1 pod has the zone and us key/value pair under a required node affinity rule:

    $ cat pod-s1.yaml

    Example output

    apiVersion: v1
    kind: Pod
    metadata:
      name: pod-s1
    spec:
      containers:
        - image: "docker.io/ocpqe/hello-pod"
          name: hello-pod
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                - key: "zone"
                  operator: In
                  values:
                  - us
    #...

  • The pod-s1 pod cannot be scheduled on Node1:

    $ oc describe pod pod-s1

    Example output

    ...
    
    Events:
     FirstSeen LastSeen Count From              SubObjectPath  Type                Reason
     --------- -------- ----- ----              -------------  --------            ------
     1m        33s      8     default-scheduler Warning        FailedScheduling    No nodes are available that match all of the following predicates:: MatchNodeSelector (1).

4.4.5. Using node affinity to control where an Operator is installed

By default, when you install an Operator, OpenShift Container Platform installs the Operator pod to one of your worker nodes randomly. However, there might be situations where you want that pod scheduled on a specific node or set of nodes.

The following examples describe situations where you might want to schedule an Operator pod to a specific node or set of nodes:

  • If an Operator requires a particular platform, such as amd64 or arm64
  • If an Operator requires a particular operating system, such as Linux or Windows
  • If you want Operators that work together scheduled on the same host or on hosts located on the same rack
  • If you want Operators dispersed throughout the infrastructure to avoid downtime due to network or hardware issues

You can control where an Operator pod is installed by adding a node affinity constraints to the Operator’s Subscription object.

The following examples show how to use node affinity to install an instance of the Custom Metrics Autoscaler Operator to a specific node in the cluster:

Node affinity example that places the Operator pod on a specific node

apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-custom-metrics-autoscaler-operator
  namespace: openshift-keda
spec:
  name: my-package
  source: my-operators
  sourceNamespace: operator-registries
  config:
    affinity:
      nodeAffinity: 1
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
              - ip-10-0-163-94.us-west-2.compute.internal
#...

1
A node affinity that requires the Operator’s pod to be scheduled on a node named ip-10-0-163-94.us-west-2.compute.internal.

Node affinity example that places the Operator pod on a node with a specific platform

apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: openshift-custom-metrics-autoscaler-operator
  namespace: openshift-keda
spec:
  name: my-package
  source: my-operators
  sourceNamespace: operator-registries
  config:
    affinity:
      nodeAffinity: 1
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: kubernetes.io/arch
              operator: In
              values:
              - arm64
            - key: kubernetes.io/os
              operator: In
              values:
              - linux
#...

1
A node affinity that requires the Operator’s pod to be scheduled on a node with the kubernetes.io/arch=arm64 and kubernetes.io/os=linux labels.

Procedure

To control the placement of an Operator pod, complete the following steps:

  1. Install the Operator as usual.
  2. If needed, ensure that your nodes are labeled to properly respond to the affinity.
  3. Edit the Operator Subscription object to add an affinity:

    apiVersion: operators.coreos.com/v1alpha1
    kind: Subscription
    metadata:
      name: openshift-custom-metrics-autoscaler-operator
      namespace: openshift-keda
    spec:
      name: my-package
      source: my-operators
      sourceNamespace: operator-registries
      config:
        affinity: 1
          nodeAffinity:
            requiredDuringSchedulingIgnoredDuringExecution:
              nodeSelectorTerms:
              - matchExpressions:
                - key: kubernetes.io/hostname
                  operator: In
                  values:
                  - ip-10-0-185-229.ec2.internal
    #...
    1
    Add a nodeAffinity.

Verification

  • To ensure that the pod is deployed on the specific node, run the following command:

    $ oc get pods -o wide

    Example output

    NAME                                                  READY   STATUS    RESTARTS   AGE   IP            NODE                           NOMINATED NODE   READINESS GATES
    custom-metrics-autoscaler-operator-5dcc45d656-bhshg   1/1     Running   0          50s   10.131.0.20   ip-10-0-185-229.ec2.internal   <none>           <none>

4.4.6. Additional resources

4.5. Placing pods onto overcommited nodes

In an overcommited state, the sum of the container compute resource requests and limits exceeds the resources available on the system. Overcommitment might be desirable in development environments where a trade-off of guaranteed performance for capacity is acceptable.

Requests and limits enable administrators to allow and manage the overcommitment of resources on a node. The scheduler uses requests for scheduling your container and providing a minimum service guarantee. Limits constrain the amount of compute resource that may be consumed on your node.

4.5.1. Understanding overcommitment

Requests and limits enable administrators to allow and manage the overcommitment of resources on a node. The scheduler uses requests for scheduling your container and providing a minimum service guarantee. Limits constrain the amount of compute resource that may be consumed on your node.

OpenShift Container Platform administrators can control the level of overcommit and manage container density on nodes by configuring masters to override the ratio between request and limit set on developer containers. In conjunction with a per-project LimitRange object specifying limits and defaults, this adjusts the container limit and request to achieve the desired level of overcommit.

Note

That these overrides have no effect if no limits have been set on containers. Create a LimitRange object with default limits, per individual project, or in the project template, to ensure that the overrides apply.

After these overrides, the container limits and requests must still be validated by any LimitRange object in the project. It is possible, for example, for developers to specify a limit close to the minimum limit, and have the request then be overridden below the minimum limit, causing the pod to be forbidden. This unfortunate user experience should be addressed with future work, but for now, configure this capability and LimitRange objects with caution.

4.5.2. Understanding nodes overcommitment

In an overcommitted environment, it is important to properly configure your node to provide best system behavior.

When the node starts, it ensures that the kernel tunable flags for memory management are set properly. The kernel should never fail memory allocations unless it runs out of physical memory.

To ensure this behavior, OpenShift Container Platform configures the kernel to always overcommit memory by setting the vm.overcommit_memory parameter to 1, overriding the default operating system setting.

OpenShift Container Platform also configures the kernel not to panic when it runs out of memory by setting the vm.panic_on_oom parameter to 0. A setting of 0 instructs the kernel to call oom_killer in an Out of Memory (OOM) condition, which kills processes based on priority

You can view the current setting by running the following commands on your nodes:

$ sysctl -a |grep commit

Example output

#...
vm.overcommit_memory = 0
#...

$ sysctl -a |grep panic

Example output

#...
vm.panic_on_oom = 0
#...

Note

The above flags should already be set on nodes, and no further action is required.

You can also perform the following configurations for each node:

  • Disable or enforce CPU limits using CPU CFS quotas
  • Reserve resources for system processes
  • Reserve memory across quality of service tiers

4.6. Controlling pod placement using node taints

Taints and tolerations allow the node to control which pods should (or should not) be scheduled on them.

4.6.1. Understanding taints and tolerations

A taint allows a node to refuse a pod to be scheduled unless that pod has a matching toleration.

You apply taints to a node through the Node specification (NodeSpec) and apply tolerations to a pod through the Pod specification (PodSpec). When you apply a taint a node, the scheduler cannot place a pod on that node unless the pod can tolerate the taint.

Example taint in a node specification

apiVersion: v1
kind: Node
metadata:
  name: my-node
#...
spec:
  taints:
  - effect: NoExecute
    key: key1
    value: value1
#...

Example toleration in a Pod spec

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
#...
spec:
  tolerations:
  - key: "key1"
    operator: "Equal"
    value: "value1"
    effect: "NoExecute"
    tolerationSeconds: 3600
#...

Taints and tolerations consist of a key, value, and effect.

Table 4.1. Taint and toleration components
ParameterDescription

key

The key is any string, up to 253 characters. The key must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores.

value

The value is any string, up to 63 characters. The value must begin with a letter or number, and may contain letters, numbers, hyphens, dots, and underscores.

effect

The effect is one of the following:

NoSchedule [1]

  • New pods that do not match the taint are not scheduled onto that node.
  • Existing pods on the node remain.

PreferNoSchedule

  • New pods that do not match the taint might be scheduled onto that node, but the scheduler tries not to.
  • Existing pods on the node remain.

NoExecute

  • New pods that do not match the taint cannot be scheduled onto that node.
  • Existing pods on the node that do not have a matching toleration are removed.

operator

Equal

The key/value/effect parameters must match. This is the default.

Exists

The key/effect parameters must match. You must leave a blank value parameter, which matches any.

  1. If you add a NoSchedule taint to a control plane node, the node must have the node-role.kubernetes.io/master=:NoSchedule taint, which is added by default.

    For example:

    apiVersion: v1
    kind: Node
    metadata:
      annotations:
        machine.openshift.io/machine: openshift-machine-api/ci-ln-62s7gtb-f76d1-v8jxv-master-0
        machineconfiguration.openshift.io/currentConfig: rendered-master-cdc1ab7da414629332cc4c3926e6e59c
      name: my-node
    #...
    spec:
      taints:
      - effect: NoSchedule
        key: node-role.kubernetes.io/master
    #...

A toleration matches a taint:

  • If the operator parameter is set to Equal:

    • the key parameters are the same;
    • the value parameters are the same;
    • the effect parameters are the same.
  • If the operator parameter is set to Exists:

    • the key parameters are the same;
    • the effect parameters are the same.

The following taints are built into OpenShift Container Platform:

  • node.kubernetes.io/not-ready: The node is not ready. This corresponds to the node condition Ready=False.
  • node.kubernetes.io/unreachable: The node is unreachable from the node controller. This corresponds to the node condition Ready=Unknown.
  • node.kubernetes.io/memory-pressure: The node has memory pressure issues. This corresponds to the node condition MemoryPressure=True.
  • node.kubernetes.io/disk-pressure: The node has disk pressure issues. This corresponds to the node condition DiskPressure=True.
  • node.kubernetes.io/network-unavailable: The node network is unavailable.
  • node.kubernetes.io/unschedulable: The node is unschedulable.
  • node.cloudprovider.kubernetes.io/uninitialized: When the node controller is started with an external cloud provider, this taint is set on a node to mark it as unusable. After a controller from the cloud-controller-manager initializes this node, the kubelet removes this taint.
  • node.kubernetes.io/pid-pressure: The node has pid pressure. This corresponds to the node condition PIDPressure=True.

    Important

    OpenShift Container Platform does not set a default pid.available evictionHard.

4.6.1.1. Understanding how to use toleration seconds to delay pod evictions

You can specify how long a pod can remain bound to a node before being evicted by specifying the tolerationSeconds parameter in the Pod specification or MachineSet object. If a taint with the NoExecute effect is added to a node, a pod that does tolerate the taint, which has the tolerationSeconds parameter, the pod is not evicted until that time period expires.

Example output

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
#...
spec:
  tolerations:
  - key: "key1"
    operator: "Equal"
    value: "value1"
    effect: "NoExecute"
    tolerationSeconds: 3600
#...

Here, if this pod is running but does not have a matching toleration, the pod stays bound to the node for 3,600 seconds and then be evicted. If the taint is removed before that time, the pod is not evicted.

4.6.1.2. Understanding how to use multiple taints

You can put multiple taints on the same node and multiple tolerations on the same pod. OpenShift Container Platform processes multiple taints and tolerations as follows:

  1. Process the taints for which the pod has a matching toleration.
  2. The remaining unmatched taints have the indicated effects on the pod:

    • If there is at least one unmatched taint with effect NoSchedule, OpenShift Container Platform cannot schedule a pod onto that node.
    • If there is no unmatched taint with effect NoSchedule but there is at least one unmatched taint with effect PreferNoSchedule, OpenShift Container Platform tries to not schedule the pod onto the node.
    • If there is at least one unmatched taint with effect NoExecute, OpenShift Container Platform evicts the pod from the node if it is already running on the node, or the pod is not scheduled onto the node if it is not yet running on the node.

      • Pods that do not tolerate the taint are evicted immediately.
      • Pods that tolerate the taint without specifying tolerationSeconds in their Pod specification remain bound forever.
      • Pods that tolerate the taint with a specified tolerationSeconds remain bound for the specified amount of time.

For example:

  • Add the following taints to the node:

    $ oc adm taint nodes node1 key1=value1:NoSchedule
    $ oc adm taint nodes node1 key1=value1:NoExecute
    $ oc adm taint nodes node1 key2=value2:NoSchedule
  • The pod has the following tolerations:

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
      - key: "key1"
        operator: "Equal"
        value: "value1"
        effect: "NoSchedule"
      - key: "key1"
        operator: "Equal"
        value: "value1"
        effect: "NoExecute"
    #...

In this case, the pod cannot be scheduled onto the node, because there is no toleration matching the third taint. The pod continues running if it is already running on the node when the taint is added, because the third taint is the only one of the three that is not tolerated by the pod.

4.6.1.3. Understanding pod scheduling and node conditions (taint node by condition)

The Taint Nodes By Condition feature, which is enabled by default, automatically taints nodes that report conditions such as memory pressure and disk pressure. If a node reports a condition, a taint is added until the condition clears. The taints have the NoSchedule effect, which means no pod can be scheduled on the node unless the pod has a matching toleration.

The scheduler checks for these taints on nodes before scheduling pods. If the taint is present, the pod is scheduled on a different node. Because the scheduler checks for taints and not the actual node conditions, you configure the scheduler to ignore some of these node conditions by adding appropriate pod tolerations.

To ensure backward compatibility, the daemon set controller automatically adds the following tolerations to all daemons:

  • node.kubernetes.io/memory-pressure
  • node.kubernetes.io/disk-pressure
  • node.kubernetes.io/unschedulable (1.10 or later)
  • node.kubernetes.io/network-unavailable (host network only)

You can also add arbitrary tolerations to daemon sets.

Note

The control plane also adds the node.kubernetes.io/memory-pressure toleration on pods that have a QoS class. This is because Kubernetes manages pods in the Guaranteed or Burstable QoS classes. The new BestEffort pods do not get scheduled onto the affected node.

4.6.1.4. Understanding evicting pods by condition (taint-based evictions)

The Taint-Based Evictions feature, which is enabled by default, evicts pods from a node that experiences specific conditions, such as not-ready and unreachable. When a node experiences one of these conditions, OpenShift Container Platform automatically adds taints to the node, and starts evicting and rescheduling the pods on different nodes.

Taint Based Evictions have a NoExecute effect, where any pod that does not tolerate the taint is evicted immediately and any pod that does tolerate the taint will never be evicted, unless the pod uses the tolerationSeconds parameter.

The tolerationSeconds parameter allows you to specify how long a pod stays bound to a node that has a node condition. If the condition still exists after the tolerationSeconds period, the taint remains on the node and the pods with a matching toleration are evicted. If the condition clears before the tolerationSeconds period, pods with matching tolerations are not removed.

If you use the tolerationSeconds parameter with no value, pods are never evicted because of the not ready and unreachable node conditions.

Note

OpenShift Container Platform evicts pods in a rate-limited way to prevent massive pod evictions in scenarios such as the master becoming partitioned from the nodes.

By default, if more than 55% of nodes in a given zone are unhealthy, the node lifecycle controller changes that zone’s state to PartialDisruption and the rate of pod evictions is reduced. For small clusters (by default, 50 nodes or less) in this state, nodes in this zone are not tainted and evictions are stopped.

For more information, see Rate limits on eviction in the Kubernetes documentation.

OpenShift Container Platform automatically adds a toleration for node.kubernetes.io/not-ready and node.kubernetes.io/unreachable with tolerationSeconds=300, unless the Pod configuration specifies either toleration.

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
#...
spec:
  tolerations:
  - key: node.kubernetes.io/not-ready
    operator: Exists
    effect: NoExecute
    tolerationSeconds: 300 1
  - key: node.kubernetes.io/unreachable
    operator: Exists
    effect: NoExecute
    tolerationSeconds: 300
#...
1
These tolerations ensure that the default pod behavior is to remain bound for five minutes after one of these node conditions problems is detected.

You can configure these tolerations as needed. For example, if you have an application with a lot of local state, you might want to keep the pods bound to node for a longer time in the event of network partition, allowing for the partition to recover and avoiding pod eviction.

Pods spawned by a daemon set are created with NoExecute tolerations for the following taints with no tolerationSeconds:

  • node.kubernetes.io/unreachable
  • node.kubernetes.io/not-ready

As a result, daemon set pods are never evicted because of these node conditions.

4.6.1.5. Tolerating all taints

You can configure a pod to tolerate all taints by adding an operator: "Exists" toleration with no key and values parameters. Pods with this toleration are not removed from a node that has taints.

Pod spec for tolerating all taints

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
#...
spec:
  tolerations:
  - operator: "Exists"
#...

4.6.2. Adding taints and tolerations

You add tolerations to pods and taints to nodes to allow the node to control which pods should or should not be scheduled on them. For existing pods and nodes, you should add the toleration to the pod first, then add the taint to the node to avoid pods being removed from the node before you can add the toleration.

Procedure

  1. Add a toleration to a pod by editing the Pod spec to include a tolerations stanza:

    Sample pod configuration file with an Equal operator

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
      - key: "key1" 1
        value: "value1"
        operator: "Equal"
        effect: "NoExecute"
        tolerationSeconds: 3600 2
    #...

    1
    The toleration parameters, as described in the Taint and toleration components table.
    2
    The tolerationSeconds parameter specifies how long a pod can remain bound to a node before being evicted.

    For example:

    Sample pod configuration file with an Exists operator

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
       tolerations:
        - key: "key1"
          operator: "Exists" 1
          effect: "NoExecute"
          tolerationSeconds: 3600
    #...

    1
    The Exists operator does not take a value.

    This example places a taint on node1 that has key key1, value value1, and taint effect NoExecute.

  2. Add a taint to a node by using the following command with the parameters described in the Taint and toleration components table:

    $ oc adm taint nodes <node_name> <key>=<value>:<effect>

    For example:

    $ oc adm taint nodes node1 key1=value1:NoExecute

    This command places a taint on node1 that has key key1, value value1, and effect NoExecute.

    Note

    If you add a NoSchedule taint to a control plane node, the node must have the node-role.kubernetes.io/master=:NoSchedule taint, which is added by default.

    For example:

    apiVersion: v1
    kind: Node
    metadata:
      annotations:
        machine.openshift.io/machine: openshift-machine-api/ci-ln-62s7gtb-f76d1-v8jxv-master-0
        machineconfiguration.openshift.io/currentConfig: rendered-master-cdc1ab7da414629332cc4c3926e6e59c
      name: my-node
    #...
    spec:
      taints:
      - effect: NoSchedule
        key: node-role.kubernetes.io/master
    #...

    The tolerations on the pod match the taint on the node. A pod with either toleration can be scheduled onto node1.

4.6.2.1. Adding taints and tolerations using a compute machine set

You can add taints to nodes using a compute machine set. All nodes associated with the MachineSet object are updated with the taint. Tolerations respond to taints added by a compute machine set in the same manner as taints added directly to the nodes.

Procedure

  1. Add a toleration to a pod by editing the Pod spec to include a tolerations stanza:

    Sample pod configuration file with Equal operator

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
      - key: "key1" 1
        value: "value1"
        operator: "Equal"
        effect: "NoExecute"
        tolerationSeconds: 3600 2
    #...

    1
    The toleration parameters, as described in the Taint and toleration components table.
    2
    The tolerationSeconds parameter specifies how long a pod is bound to a node before being evicted.

    For example:

    Sample pod configuration file with Exists operator

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
      - key: "key1"
        operator: "Exists"
        effect: "NoExecute"
        tolerationSeconds: 3600
    #...

  2. Add the taint to the MachineSet object:

    1. Edit the MachineSet YAML for the nodes you want to taint or you can create a new MachineSet object:

      $ oc edit machineset <machineset>
    2. Add the taint to the spec.template.spec section:

      Example taint in a compute machine set specification

      apiVersion: machine.openshift.io/v1beta1
      kind: MachineSet
      metadata:
        name: my-machineset
      #...
      spec:
      #...
        template:
      #...
          spec:
            taints:
            - effect: NoExecute
              key: key1
              value: value1
      #...

      This example places a taint that has the key key1, value value1, and taint effect NoExecute on the nodes.

    3. Scale down the compute machine set to 0:

      $ oc scale --replicas=0 machineset <machineset> -n openshift-machine-api
      Tip

      You can alternatively apply the following YAML to scale the compute machine set:

      apiVersion: machine.openshift.io/v1beta1
      kind: MachineSet
      metadata:
        name: <machineset>
        namespace: openshift-machine-api
      spec:
        replicas: 0

      Wait for the machines to be removed.

    4. Scale up the compute machine set as needed:

      $ oc scale --replicas=2 machineset <machineset> -n openshift-machine-api

      Or:

      $ oc edit machineset <machineset> -n openshift-machine-api

      Wait for the machines to start. The taint is added to the nodes associated with the MachineSet object.

4.6.2.2. Binding a user to a node using taints and tolerations

If you want to dedicate a set of nodes for exclusive use by a particular set of users, add a toleration to their pods. Then, add a corresponding taint to those nodes. The pods with the tolerations are allowed to use the tainted nodes or any other nodes in the cluster.

If you want ensure the pods are scheduled to only those tainted nodes, also add a label to the same set of nodes and add a node affinity to the pods so that the pods can only be scheduled onto nodes with that label.

Procedure

To configure a node so that users can use only that node:

  1. Add a corresponding taint to those nodes:

    For example:

    $ oc adm taint nodes node1 dedicated=groupName:NoSchedule
    Tip

    You can alternatively apply the following YAML to add the taint:

    kind: Node
    apiVersion: v1
    metadata:
      name: my-node
    #...
    spec:
      taints:
        - key: dedicated
          value: groupName
          effect: NoSchedule
    #...
  2. Add a toleration to the pods by writing a custom admission controller.
4.6.2.3. Creating a project with a node selector and toleration

You can create a project that uses a node selector and toleration, which are set as annotations, to control the placement of pods onto specific nodes. Any subsequent resources created in the project are then scheduled on nodes that have a taint matching the toleration.

Prerequisites

  • A label for node selection has been added to one or more nodes by using a compute machine set or editing the node directly.
  • A taint has been added to one or more nodes by using a compute machine set or editing the node directly.

Procedure

  1. Create a Project resource definition, specifying a node selector and toleration in the metadata.annotations section:

    Example project.yaml file

    kind: Project
    apiVersion: project.openshift.io/v1
    metadata:
      name: <project_name> 1
      annotations:
        openshift.io/node-selector: '<label>' 2
        scheduler.alpha.kubernetes.io/defaultTolerations: >-
          [{"operator": "Exists", "effect": "NoSchedule", "key":
          "<key_name>"} 3
          ]

    1
    The project name.
    2
    The default node selector label.
    3
    The toleration parameters, as described in the Taint and toleration components table. This example uses the NoSchedule effect, which allows existing pods on the node to remain, and the Exists operator, which does not take a value.
  2. Use the oc apply command to create the project:

    $ oc apply -f project.yaml

Any subsequent resources created in the <project_name> namespace should now be scheduled on the specified nodes.

4.6.2.4. Controlling nodes with special hardware using taints and tolerations

In a cluster where a small subset of nodes have specialized hardware, you can use taints and tolerations to keep pods that do not need the specialized hardware off of those nodes, leaving the nodes for pods that do need the specialized hardware. You can also require pods that need specialized hardware to use specific nodes.

You can achieve this by adding a toleration to pods that need the special hardware and tainting the nodes that have the specialized hardware.

Procedure

To ensure nodes with specialized hardware are reserved for specific pods:

  1. Add a toleration to pods that need the special hardware.

    For example:

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
        - key: "disktype"
          value: "ssd"
          operator: "Equal"
          effect: "NoSchedule"
          tolerationSeconds: 3600
    #...
  2. Taint the nodes that have the specialized hardware using one of the following commands:

    $ oc adm taint nodes <node-name> disktype=ssd:NoSchedule

    Or:

    $ oc adm taint nodes <node-name> disktype=ssd:PreferNoSchedule
    Tip

    You can alternatively apply the following YAML to add the taint:

    kind: Node
    apiVersion: v1
    metadata:
      name: my_node
    #...
    spec:
      taints:
        - key: disktype
          value: ssd
          effect: PreferNoSchedule
    #...

4.6.3. Removing taints and tolerations

You can remove taints from nodes and tolerations from pods as needed. You should add the toleration to the pod first, then add the taint to the node to avoid pods being removed from the node before you can add the toleration.

Procedure

To remove taints and tolerations:

  1. To remove a taint from a node:

    $ oc adm taint nodes <node-name> <key>-

    For example:

    $ oc adm taint nodes ip-10-0-132-248.ec2.internal key1-

    Example output

    node/ip-10-0-132-248.ec2.internal untainted

  2. To remove a toleration from a pod, edit the Pod spec to remove the toleration:

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-pod
    #...
    spec:
      tolerations:
      - key: "key2"
        operator: "Exists"
        effect: "NoExecute"
        tolerationSeconds: 3600
    #...

4.7. Placing pods on specific nodes using node selectors

A node selector specifies a map of key/value pairs that are defined using custom labels on nodes and selectors specified in pods.

For the pod to be eligible to run on a node, the pod must have the same key/value node selector as the label on the node.

4.7.1. About node selectors

You can use node selectors on pods and labels on nodes to control where the pod is scheduled. With node selectors, OpenShift Container Platform schedules the pods on nodes that contain matching labels.

You can use a node selector to place specific pods on specific nodes, cluster-wide node selectors to place new pods on specific nodes anywhere in the cluster, and project node selectors to place new pods in a project on specific nodes.

For example, as a cluster administrator, you can create an infrastructure where application developers can deploy pods only onto the nodes closest to their geographical location by including a node selector in every pod they create. In this example, the cluster consists of five data centers spread across two regions. In the U.S., label the nodes as us-east, us-central, or us-west. In the Asia-Pacific region (APAC), label the nodes as apac-east or apac-west. The developers can add a node selector to the pods they create to ensure the pods get scheduled on those nodes.

A pod is not scheduled if the Pod object contains a node selector, but no node has a matching label.

Important

If you are using node selectors and node affinity in the same pod configuration, the following rules control pod placement onto nodes:

  • If you configure both nodeSelector and nodeAffinity, both conditions must be satisfied for the pod to be scheduled onto a candidate node.
  • If you specify multiple nodeSelectorTerms associated with nodeAffinity types, then the pod can be scheduled onto a node if one of the nodeSelectorTerms is satisfied.
  • If you specify multiple matchExpressions associated with nodeSelectorTerms, then the pod can be scheduled onto a node only if all matchExpressions are satisfied.
Node selectors on specific pods and nodes

You can control which node a specific pod is scheduled on by using node selectors and labels.

To use node selectors and labels, first label the node to avoid pods being descheduled, then add the node selector to the pod.

Note

You cannot add a node selector directly to an existing scheduled pod. You must label the object that controls the pod, such as deployment config.

For example, the following Node object has the region: east label:

Sample Node object with a label

kind: Node
apiVersion: v1
metadata:
  name: ip-10-0-131-14.ec2.internal
  selfLink: /api/v1/nodes/ip-10-0-131-14.ec2.internal
  uid: 7bc2580a-8b8e-11e9-8e01-021ab4174c74
  resourceVersion: '478704'
  creationTimestamp: '2019-06-10T14:46:08Z'
  labels:
    kubernetes.io/os: linux
    failure-domain.beta.kubernetes.io/zone: us-east-1a
    node.openshift.io/os_version: '4.5'
    node-role.kubernetes.io/worker: ''
    failure-domain.beta.kubernetes.io/region: us-east-1
    node.openshift.io/os_id: rhcos
    beta.kubernetes.io/instance-type: m4.large
    kubernetes.io/hostname: ip-10-0-131-14
    beta.kubernetes.io/arch: amd64
    region: east 1
    type: user-node
#...

1
Labels to match the pod node selector.

A pod has the type: user-node,region: east node selector:

Sample Pod object with node selectors

apiVersion: v1
kind: Pod
metadata:
  name: s1
#...
spec:
  nodeSelector: 1
    region: east
    type: user-node
#...

1
Node selectors to match the node label. The node must have a label for each node selector.

When you create the pod using the example pod spec, it can be scheduled on the example node.

Default cluster-wide node selectors

With default cluster-wide node selectors, when you create a pod in that cluster, OpenShift Container Platform adds the default node selectors to the pod and schedules the pod on nodes with matching labels.

For example, the following Scheduler object has the default cluster-wide region=east and type=user-node node selectors:

Example Scheduler Operator Custom Resource

apiVersion: config.openshift.io/v1
kind: Scheduler
metadata:
  name: cluster
#...
spec:
  defaultNodeSelector: type=user-node,region=east
#...

A node in that cluster has the type=user-node,region=east labels:

Example Node object

apiVersion: v1
kind: Node
metadata:
  name: ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4
#...
  labels:
    region: east
    type: user-node
#...

Example Pod object with a node selector

apiVersion: v1
kind: Pod
metadata:
  name: s1
#...
spec:
  nodeSelector:
    region: east
#...

When you create the pod using the example pod spec in the example cluster, the pod is created with the cluster-wide node selector and is scheduled on the labeled node:

Example pod list with the pod on the labeled node

NAME     READY   STATUS    RESTARTS   AGE   IP           NODE                                       NOMINATED NODE   READINESS GATES
pod-s1   1/1     Running   0          20s   10.131.2.6   ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4   <none>           <none>

Note

If the project where you create the pod has a project node selector, that selector takes preference over a cluster-wide node selector. Your pod is not created or scheduled if the pod does not have the project node selector.

Project node selectors

With project node selectors, when you create a pod in this project, OpenShift Container Platform adds the node selectors to the pod and schedules the pods on a node with matching labels. If there is a cluster-wide default node selector, a project node selector takes preference.

For example, the following project has the region=east node selector:

Example Namespace object

apiVersion: v1
kind: Namespace
metadata:
  name: east-region
  annotations:
    openshift.io/node-selector: "region=east"
#...

The following node has the type=user-node,region=east labels:

Example Node object

apiVersion: v1
kind: Node
metadata:
  name: ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4
#...
  labels:
    region: east
    type: user-node
#...

When you create the pod using the example pod spec in this example project, the pod is created with the project node selectors and is scheduled on the labeled node:

Example Pod object

apiVersion: v1
kind: Pod
metadata:
  namespace: east-region
#...
spec:
  nodeSelector:
    region: east
    type: user-node
#...

Example pod list with the pod on the labeled node

NAME     READY   STATUS    RESTARTS   AGE   IP           NODE                                       NOMINATED NODE   READINESS GATES
pod-s1   1/1     Running   0          20s   10.131.2.6   ci-ln-qg1il3k-f76d1-hlmhl-worker-b-df2s4   <none>           <none>

A pod in the project is not created or scheduled if the pod contains different node selectors. For example, if you deploy the following pod into the example project, it is not be created:

Example Pod object with an invalid node selector

apiVersion: v1
kind: Pod
metadata:
  name: west-region
#...
spec:
  nodeSelector:
    region: west
#...

4.7.2. Using node selectors to control pod placement

You can use node selectors on pods and labels on nodes to control where the pod is scheduled. With node selectors, OpenShift Container Platform schedules the pods on nodes that contain matching labels.

You add labels to a node, a compute machine set, or a machine config. Adding the label to the compute machine set ensures that if the node or machine goes down, new nodes have the label. Labels added to a node or machine config do not persist if the node or machine goes down.

To add node selectors to an existing pod, add a node selector to the controlling object for that pod, such as a ReplicaSet object, DaemonSet object, StatefulSet object, Deployment object, or DeploymentConfig object. Any existing pods under that controlling object are recreated on a node with a matching label. If you are creating a new pod, you can add the node selector directly to the pod spec. If the pod does not have a controlling object, you must delete the pod, edit the pod spec, and recreate the pod.

Note

You cannot add a node selector directly to an existing scheduled pod.

Prerequisites

To add a node selector to existing pods, determine the controlling object for that pod. For example, the router-default-66d5cf9464-m2g75 pod is controlled by the router-default-66d5cf9464 replica set:

$ oc describe pod router-default-66d5cf9464-7pwkc

Example output

kind: Pod
apiVersion: v1
metadata:
#...
Name:               router-default-66d5cf9464-7pwkc
Namespace:          openshift-ingress
# ...
Controlled By:      ReplicaSet/router-default-66d5cf9464
# ...

The web console lists the controlling object under ownerReferences in the pod YAML:

apiVersion: v1
kind: Pod
metadata:
  name: router-default-66d5cf9464-7pwkc
# ...
  ownerReferences:
    - apiVersion: apps/v1
      kind: ReplicaSet
      name: router-default-66d5cf9464
      uid: d81dd094-da26-11e9-a48a-128e7edf0312
      controller: true
      blockOwnerDeletion: true
# ...

Procedure

  1. Add labels to a node by using a compute machine set or editing the node directly:

    • Use a MachineSet object to add labels to nodes managed by the compute machine set when a node is created:

      1. Run the following command to add labels to a MachineSet object:

        $ oc patch MachineSet <name> --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"<key>"="<value>","<key>"="<value>"}}]'  -n openshift-machine-api

        For example:

        $ oc patch MachineSet abc612-msrtw-worker-us-east-1c  --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"type":"user-node","region":"east"}}]'  -n openshift-machine-api
        Tip

        You can alternatively apply the following YAML to add labels to a compute machine set:

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        metadata:
          name: xf2bd-infra-us-east-2a
          namespace: openshift-machine-api
        spec:
          template:
            spec:
              metadata:
                labels:
                  region: "east"
                  type: "user-node"
        #...
      2. Verify that the labels are added to the MachineSet object by using the oc edit command:

        For example:

        $ oc edit MachineSet abc612-msrtw-worker-us-east-1c -n openshift-machine-api

        Example MachineSet object

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        
        # ...
        
        spec:
        # ...
          template:
            metadata:
        # ...
            spec:
              metadata:
                labels:
                  region: east
                  type: user-node
        # ...

    • Add labels directly to a node:

      1. Edit the Node object for the node:

        $ oc label nodes <name> <key>=<value>

        For example, to label a node:

        $ oc label nodes ip-10-0-142-25.ec2.internal type=user-node region=east
        Tip

        You can alternatively apply the following YAML to add labels to a node:

        kind: Node
        apiVersion: v1
        metadata:
          name: hello-node-6fbccf8d9
          labels:
            type: "user-node"
            region: "east"
        #...
      2. Verify that the labels are added to the node:

        $ oc get nodes -l type=user-node,region=east

        Example output

        NAME                          STATUS   ROLES    AGE   VERSION
        ip-10-0-142-25.ec2.internal   Ready    worker   17m   v1.25.0

  2. Add the matching node selector to a pod:

    • To add a node selector to existing and future pods, add a node selector to the controlling object for the pods:

      Example ReplicaSet object with labels

      kind: ReplicaSet
      apiVersion: apps/v1
      metadata:
        name: hello-node-6fbccf8d9
      # ...
      spec:
      # ...
        template:
          metadata:
            creationTimestamp: null
            labels:
              ingresscontroller.operator.openshift.io/deployment-ingresscontroller: default
              pod-template-hash: 66d5cf9464
          spec:
            nodeSelector:
              kubernetes.io/os: linux
              node-role.kubernetes.io/worker: ''
              type: user-node 1
      #...

      1
      Add the node selector.
    • To add a node selector to a specific, new pod, add the selector to the Pod object directly:

      Example Pod object with a node selector

      apiVersion: v1
      kind: Pod
      metadata:
        name: hello-node-6fbccf8d9
      #...
      spec:
        nodeSelector:
          region: east
          type: user-node
      #...

      Note

      You cannot add a node selector directly to an existing scheduled pod.

4.7.3. Creating default cluster-wide node selectors

You can use default cluster-wide node selectors on pods together with labels on nodes to constrain all pods created in a cluster to specific nodes.

With cluster-wide node selectors, when you create a pod in that cluster, OpenShift Container Platform adds the default node selectors to the pod and schedules the pod on nodes with matching labels.

You configure cluster-wide node selectors by editing the Scheduler Operator custom resource (CR). You add labels to a node, a compute machine set, or a machine config. Adding the label to the compute machine set ensures that if the node or machine goes down, new nodes have the label. Labels added to a node or machine config do not persist if the node or machine goes down.

Note

You can add additional key/value pairs to a pod. But you cannot add a different value for a default key.

Procedure

To add a default cluster-wide node selector:

  1. Edit the Scheduler Operator CR to add the default cluster-wide node selectors:

    $ oc edit scheduler cluster

    Example Scheduler Operator CR with a node selector

    apiVersion: config.openshift.io/v1
    kind: Scheduler
    metadata:
      name: cluster
    ...
    spec:
      defaultNodeSelector: type=user-node,region=east 1
      mastersSchedulable: false

    1
    Add a node selector with the appropriate <key>:<value> pairs.

    After making this change, wait for the pods in the openshift-kube-apiserver project to redeploy. This can take several minutes. The default cluster-wide node selector does not take effect until the pods redeploy.

  2. Add labels to a node by using a compute machine set or editing the node directly:

    • Use a compute machine set to add labels to nodes managed by the compute machine set when a node is created:

      1. Run the following command to add labels to a MachineSet object:

        $ oc patch MachineSet <name> --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"<key>"="<value>","<key>"="<value>"}}]'  -n openshift-machine-api 1
        1
        Add a <key>/<value> pair for each label.

        For example:

        $ oc patch MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"type":"user-node","region":"east"}}]'  -n openshift-machine-api
        Tip

        You can alternatively apply the following YAML to add labels to a compute machine set:

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        metadata:
          name: <machineset>
          namespace: openshift-machine-api
        spec:
          template:
            spec:
              metadata:
                labels:
                  region: "east"
                  type: "user-node"
      2. Verify that the labels are added to the MachineSet object by using the oc edit command:

        For example:

        $ oc edit MachineSet abc612-msrtw-worker-us-east-1c -n openshift-machine-api

        Example MachineSet object

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
          ...
        spec:
          ...
          template:
            metadata:
          ...
            spec:
              metadata:
                labels:
                  region: east
                  type: user-node
          ...

      3. Redeploy the nodes associated with that compute machine set by scaling down to 0 and scaling up the nodes:

        For example:

        $ oc scale --replicas=0 MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c -n openshift-machine-api
        $ oc scale --replicas=1 MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c -n openshift-machine-api
      4. When the nodes are ready and available, verify that the label is added to the nodes by using the oc get command:

        $ oc get nodes -l <key>=<value>

        For example:

        $ oc get nodes -l type=user-node

        Example output

        NAME                                       STATUS   ROLES    AGE   VERSION
        ci-ln-l8nry52-f76d1-hl7m7-worker-c-vmqzp   Ready    worker   61s   v1.25.0

    • Add labels directly to a node:

      1. Edit the Node object for the node:

        $ oc label nodes <name> <key>=<value>

        For example, to label a node:

        $ oc label nodes ci-ln-l8nry52-f76d1-hl7m7-worker-b-tgq49 type=user-node region=east
        Tip

        You can alternatively apply the following YAML to add labels to a node:

        kind: Node
        apiVersion: v1
        metadata:
          name: <node_name>
          labels:
            type: "user-node"
            region: "east"
      2. Verify that the labels are added to the node using the oc get command:

        $ oc get nodes -l <key>=<value>,<key>=<value>

        For example:

        $ oc get nodes -l type=user-node,region=east

        Example output

        NAME                                       STATUS   ROLES    AGE   VERSION
        ci-ln-l8nry52-f76d1-hl7m7-worker-b-tgq49   Ready    worker   17m   v1.25.0

4.7.4. Creating project-wide node selectors

You can use node selectors in a project together with labels on nodes to constrain all pods created in that project to the labeled nodes.

When you create a pod in this project, OpenShift Container Platform adds the node selectors to the pods in the project and schedules the pods on a node with matching labels in the project. If there is a cluster-wide default node selector, a project node selector takes preference.

You add node selectors to a project by editing the Namespace object to add the openshift.io/node-selector parameter. You add labels to a node, a compute machine set, or a machine config. Adding the label to the compute machine set ensures that if the node or machine goes down, new nodes have the label. Labels added to a node or machine config do not persist if the node or machine goes down.

A pod is not scheduled if the Pod object contains a node selector, but no project has a matching node selector. When you create a pod from that spec, you receive an error similar to the following message:

Example error message

Error from server (Forbidden): error when creating "pod.yaml": pods "pod-4" is forbidden: pod node label selector conflicts with its project node label selector

Note

You can add additional key/value pairs to a pod. But you cannot add a different value for a project key.

Procedure

To add a default project node selector:

  1. Create a namespace or edit an existing namespace to add the openshift.io/node-selector parameter:

    $ oc edit namespace <name>

    Example output

    apiVersion: v1
    kind: Namespace
    metadata:
      annotations:
        openshift.io/node-selector: "type=user-node,region=east" 1
        openshift.io/description: ""
        openshift.io/display-name: ""
        openshift.io/requester: kube:admin
        openshift.io/sa.scc.mcs: s0:c30,c5
        openshift.io/sa.scc.supplemental-groups: 1000880000/10000
        openshift.io/sa.scc.uid-range: 1000880000/10000
      creationTimestamp: "2021-05-10T12:35:04Z"
      labels:
        kubernetes.io/metadata.name: demo
      name: demo
      resourceVersion: "145537"
      uid: 3f8786e3-1fcb-42e3-a0e3-e2ac54d15001
    spec:
      finalizers:
      - kubernetes

    1
    Add the openshift.io/node-selector with the appropriate <key>:<value> pairs.
  2. Add labels to a node by using a compute machine set or editing the node directly:

    • Use a MachineSet object to add labels to nodes managed by the compute machine set when a node is created:

      1. Run the following command to add labels to a MachineSet object:

        $ oc patch MachineSet <name> --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"<key>"="<value>","<key>"="<value>"}}]'  -n openshift-machine-api

        For example:

        $ oc patch MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c --type='json' -p='[{"op":"add","path":"/spec/template/spec/metadata/labels", "value":{"type":"user-node","region":"east"}}]'  -n openshift-machine-api
        Tip

        You can alternatively apply the following YAML to add labels to a compute machine set:

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        metadata:
          name: <machineset>
          namespace: openshift-machine-api
        spec:
          template:
            spec:
              metadata:
                labels:
                  region: "east"
                  type: "user-node"
      2. Verify that the labels are added to the MachineSet object by using the oc edit command:

        For example:

        $ oc edit MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c -n openshift-machine-api

        Example output

        apiVersion: machine.openshift.io/v1beta1
        kind: MachineSet
        metadata:
        ...
        spec:
        ...
          template:
            metadata:
        ...
            spec:
              metadata:
                labels:
                  region: east
                  type: user-node

      3. Redeploy the nodes associated with that compute machine set:

        For example:

        $ oc scale --replicas=0 MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c -n openshift-machine-api
        $ oc scale --replicas=1 MachineSet ci-ln-l8nry52-f76d1-hl7m7-worker-c -n openshift-machine-api
      4. When the nodes are ready and available, verify that the label is added to the nodes by using the oc get command:

        $ oc get nodes -l <key>=<value>

        For example:

        $ oc get nodes -l type=user-node,region=east

        Example output

        NAME                                       STATUS   ROLES    AGE   VERSION
        ci-ln-l8nry52-f76d1-hl7m7-worker-c-vmqzp   Ready    worker   61s   v1.25.0

    • Add labels directly to a node:

      1. Edit the Node object to add labels:

        $ oc label <resource> <name> <key>=<value>

        For example, to label a node:

        $ oc label nodes ci-ln-l8nry52-f76d1-hl7m7-worker-c-tgq49 type=user-node region=east
        Tip

        You can alternatively apply the following YAML to add labels to a node:

        kind: Node
        apiVersion: v1
        metadata:
          name: <node_name>
          labels:
            type: "user-node"
            region: "east"
      2. Verify that the labels are added to the Node object using the oc get command:

        $ oc get nodes -l <key>=<value>

        For example:

        $ oc get nodes -l type=user-node,region=east

        Example output

        NAME                                       STATUS   ROLES    AGE   VERSION
        ci-ln-l8nry52-f76d1-hl7m7-worker-b-tgq49   Ready    worker   17m   v1.25.0

4.8. Controlling pod placement by using pod topology spread constraints

You can use pod topology spread constraints to provide fine-grained control over the placement of your pods across nodes, zones, regions, or other user-defined topology domains. Distributing pods across failure domains can help to achieve high availability and more efficient resource utilization.

4.8.1. Example use cases

  • As an administrator, I want my workload to automatically scale between two to fifteen pods. I want to ensure that when there are only two pods, they are not placed on the same node, to avoid a single point of failure.
  • As an administrator, I want to distribute my pods evenly across multiple infrastructure zones to reduce latency and network costs. I want to ensure that my cluster can self-heal if issues arise.

4.8.2. Important considerations

  • Pods in an OpenShift Container Platform cluster are managed by workload controllers such as deployments, stateful sets, or daemon sets. These controllers define the desired state for a group of pods, including how they are distributed and scaled across the nodes in the cluster. You should set the same pod topology spread constraints on all pods in a group to avoid confusion. When using a workload controller, such as a deployment, the pod template typically handles this for you.
  • Mixing different pod topology spread constraints can make OpenShift Container Platform behavior confusing and troubleshooting more difficult. You can avoid this by ensuring that all nodes in a topology domain are consistently labeled. OpenShift Container Platform automatically populates well-known labels, such as kubernetes.io/hostname. This helps avoid the need for manual labeling of nodes. These labels provide essential topology information, ensuring consistent node labeling across the cluster.
  • Only pods within the same namespace are matched and grouped together when spreading due to a constraint.
  • You can specify multiple pod topology spread constraints, but you must ensure that they do not conflict with each other. All pod topology spread constraints must be satisfied for a pod to be placed.

4.8.3. Understanding skew and maxSkew

Skew refers to the difference in the number of pods that match a specified label selector across different topology domains, such as zones or nodes.

The skew is calculated for each domain by taking the absolute difference between the number of pods in that domain and the number of pods in the domain with the lowest amount of pods scheduled. Setting a maxSkew value guides the scheduler to maintain a balanced pod distribution.

4.8.3.1. Example skew calculation

You have three zones (A, B, and C), and you want to distribute your pods evenly across these zones. If zone A has 5 pods, zone B has 3 pods, and zone C has 2 pods, to find the skew, you can subtract the number of pods in the domain with the lowest amount of pods scheduled from the number of pods currently in each zone. This means that the skew for zone A is 3, the skew for zone B is 1, and the skew for zone C is 0.

4.8.3.2. The maxSkew parameter

The maxSkew parameter defines the maximum allowable difference, or skew, in the number of pods between any two topology domains. If maxSkew is set to 1, the number of pods in any topology domain should not differ by more than 1 from any other domain. If the skew exceeds maxSkew, the scheduler attempts to place new pods in a way that reduces the skew, adhering to the constraints.

Using the previous example skew calculation, the skew values exceed the default maxSkew value of 1. The scheduler places new pods in zone B and zone C to reduce the skew and achieve a more balanced distribution, ensuring that no topology domain exceeds the skew of 1.

4.8.4. Example configurations for pod topology spread constraints

You can specify which pods to group together, which topology domains they are spread among, and the acceptable skew.

The following examples demonstrate pod topology spread constraint configurations.

Example to distribute pods that match the specified labels based on their zone

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
  labels:
    region: us-east
spec:
  securityContext:
    runAsNonRoot: true
    seccompProfile:
      type: RuntimeDefault
  topologySpreadConstraints:
  - maxSkew: 1 1
    topologyKey: topology.kubernetes.io/zone 2
    whenUnsatisfiable: DoNotSchedule 3
    labelSelector: 4
      matchLabels:
        region: us-east 5
    matchLabelKeys:
      - my-pod-label 6
  containers:
  - image: "docker.io/ocpqe/hello-pod"
    name: hello-pod
    securityContext:
      allowPrivilegeEscalation: false
      capabilities:
        drop: [ALL]

1
The maximum difference in number of pods between any two topology domains. The default is 1, and you cannot specify a value of 0.
2
The key of a node label. Nodes with this key and identical value are considered to be in the same topology.
3
How to handle a pod if it does not satisfy the spread constraint. The default is DoNotSchedule, which tells the scheduler not to schedule the pod. Set to ScheduleAnyway to still schedule the pod, but the scheduler prioritizes honoring the skew to not make the cluster more imbalanced.
4
Pods that match this label selector are counted and recognized as a group when spreading to satisfy the constraint. Be sure to specify a label selector, otherwise no pods can be matched.
5
Be sure that this Pod spec also sets its labels to match this label selector if you want it to be counted properly in the future.
6
A list of pod label keys to select which pods to calculate spreading over.

Example demonstrating a single pod topology spread constraint

kind: Pod
apiVersion: v1
metadata:
  name: my-pod
  labels:
    region: us-east
spec:
  topologySpreadConstraints:
  - maxSkew: 1
    topologyKey: topology.kubernetes.io/zone
    whenUnsatisfiable: DoNotSchedule
    labelSelector:
      matchLabels:
        region: us-east
  containers:
  - image: "docker.io/ocpqe/hello-pod"
    name: hello-pod

The previous example defines a Pod spec with a one pod topology spread constraint. It matches on pods labeled region: us-east, distributes among zones, specifies a skew of 1, and does not schedule the pod if it does not meet these requirements.

Example demonstrating multiple pod topology spread constraints

kind: Pod
apiVersion: v1
metadata:
  name: my-pod-2
  labels:
    region: us-east
spec:
  topologySpreadConstraints:
  - maxSkew: 1
    topologyKey: node
    whenUnsatisfiable: DoNotSchedule
    labelSelector:
      matchLabels:
        region: us-east
  - maxSkew: 1
    topologyKey: rack
    whenUnsatisfiable: DoNotSchedule
    labelSelector:
      matchLabels:
        region: us-east
  containers:
  - image: "docker.io/ocpqe/hello-pod"
    name: hello-pod

The previous example defines a Pod spec with two pod topology spread constraints. Both match on pods labeled region: us-east, specify a skew of 1, and do not schedule the pod if it does not meet these requirements.

The first constraint distributes pods based on a user-defined label node, and the second constraint distributes pods based on a user-defined label rack. Both constraints must be met for the pod to be scheduled.

4.8.5. Additional resources

4.9. Evicting pods using the descheduler

While the scheduler is used to determine the most suitable node to host a new pod, the descheduler can be used to evict a running pod so that the pod can be rescheduled onto a more suitable node.

4.9.1. About the descheduler

You can use the descheduler to evict pods based on specific strategies so that the pods can be rescheduled onto more appropriate nodes.

You can benefit from descheduling running pods in situations such as the following:

  • Nodes are underutilized or overutilized.
  • Pod and node affinity requirements, such as taints or labels, have changed and the original scheduling decisions are no longer appropriate for certain nodes.
  • Node failure requires pods to be moved.
  • New nodes are added to clusters.
  • Pods have been restarted too many times.
Important

The descheduler does not schedule replacement of evicted pods. The scheduler automatically performs this task for the evicted pods.

When the descheduler decides to evict pods from a node, it employs the following general mechanism:

  • Pods in the openshift-* and kube-system namespaces are never evicted.
  • Critical pods with priorityClassName set to system-cluster-critical or system-node-critical are never evicted.
  • Static, mirrored, or stand-alone pods that are not part of a replication controller, replica set, deployment, StatefulSet, or job are never evicted because these pods will not be recreated.
  • Pods associated with daemon sets are never evicted.
  • Pods with local storage are never evicted.
  • Best effort pods are evicted before burstable and guaranteed pods.
  • All types of pods with the descheduler.alpha.kubernetes.io/evict annotation are eligible for eviction. This annotation is used to override checks that prevent eviction, and the user can select which pod is evicted. Users should know how and if the pod will be recreated.
  • Pods subject to pod disruption budget (PDB) are not evicted if descheduling violates its pod disruption budget (PDB). The pods are evicted by using eviction subresource to handle PDB.

4.9.2. Descheduler profiles

The following descheduler profiles are available:

AffinityAndTaints

This profile evicts pods that violate inter-pod anti-affinity, node affinity, and node taints.

It enables the following strategies:

  • RemovePodsViolatingInterPodAntiAffinity: removes pods that are violating inter-pod anti-affinity.
  • RemovePodsViolatingNodeAffinity: removes pods that are violating node affinity.
  • RemovePodsViolatingNodeTaints: removes pods that are violating NoSchedule taints on nodes.

    Pods with a node affinity type of requiredDuringSchedulingIgnoredDuringExecution are removed.

TopologyAndDuplicates

This profile evicts pods in an effort to evenly spread similar pods, or pods of the same topology domain, among nodes.

It enables the following strategies:

  • RemovePodsViolatingTopologySpreadConstraint: finds unbalanced topology domains and tries to evict pods from larger ones when DoNotSchedule constraints are violated.
  • RemoveDuplicates: ensures that there is only one pod associated with a replica set, replication controller, deployment, or job running on same node. If there are more, those duplicate pods are evicted for better pod distribution in a cluster.
LifecycleAndUtilization

This profile evicts long-running pods and balances resource usage between nodes.

It enables the following strategies:

  • RemovePodsHavingTooManyRestarts: removes pods whose containers have been restarted too many times.

    Pods where the sum of restarts over all containers (including Init Containers) is more than 100.

  • LowNodeUtilization: finds nodes that are underutilized and evicts pods, if possible, from overutilized nodes in the hope that recreation of evicted pods will be scheduled on these underutilized nodes.

    A node is considered underutilized if its usage is below 20% for all thresholds (CPU, memory, and number of pods).

    A node is considered overutilized if its usage is above 50% for any of the thresholds (CPU, memory, and number of pods).

  • PodLifeTime: evicts pods that are too old.

    By default, pods that are older than 24 hours are removed. You can customize the pod lifetime value.

SoftTopologyAndDuplicates

This profile is the same as TopologyAndDuplicates, except that pods with soft topology constraints, such as whenUnsatisfiable: ScheduleAnyway, are also considered for eviction.

Note

Do not enable both SoftTopologyAndDuplicates and TopologyAndDuplicates. Enabling both results in a conflict.

EvictPodsWithLocalStorage
This profile allows pods with local storage to be eligible for eviction.
EvictPodsWithPVC
This profile allows pods with persistent volume claims to be eligible for eviction. If you are using Kubernetes NFS Subdir External Provisioner, you must add an excluded namespace for the namespace where the provisioner is installed.

4.9.3. Installing the descheduler

The descheduler is not available by default. To enable the descheduler, you must install the Kube Descheduler Operator from OperatorHub and enable one or more descheduler profiles.

By default, the descheduler runs in predictive mode, which means that it only simulates pod evictions. You must change the mode to automatic for the descheduler to perform the pod evictions.

Important

If you have enabled hosted control planes in your cluster, set a custom priority threshold to lower the chance that pods in the hosted control plane namespaces are evicted. Set the priority threshold class name to hypershift-control-plane, because it has the lowest priority value (100000000) of the hosted control plane priority classes.

Prerequisites

  • Cluster administrator privileges.
  • Access to the OpenShift Container Platform web console.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Create the required namespace for the Kube Descheduler Operator.

    1. Navigate to AdministrationNamespaces and click Create Namespace.
    2. Enter openshift-kube-descheduler-operator in the Name field, enter openshift.io/cluster-monitoring=true in the Labels field to enable descheduler metrics, and click Create.
  3. Install the Kube Descheduler Operator.

    1. Navigate to OperatorsOperatorHub.
    2. Type Kube Descheduler Operator into the filter box.
    3. Select the Kube Descheduler Operator and click Install.
    4. On the Install Operator page, select A specific namespace on the cluster. Select openshift-kube-descheduler-operator from the drop-down menu.
    5. Adjust the values for the Update Channel and Approval Strategy to the desired values.
    6. Click Install.
  4. Create a descheduler instance.

    1. From the OperatorsInstalled Operators page, click the Kube Descheduler Operator.
    2. Select the Kube Descheduler tab and click Create KubeDescheduler.
    3. Edit the settings as necessary.

      1. To evict pods instead of simulating the evictions, change the Mode field to Automatic.
      2. Expand the Profiles section to select one or more profiles to enable. The AffinityAndTaints profile is enabled by default. Click Add Profile to select additional profiles.

        Note

        Do not enable both TopologyAndDuplicates and SoftTopologyAndDuplicates. Enabling both results in a conflict.

      3. Optional: Expand the Profile Customizations section to set optional configurations for the descheduler.

        • Set a custom pod lifetime value for the LifecycleAndUtilization profile. Use the podLifetime field to set a numerical value and a valid unit (s, m, or h). The default pod lifetime is 24 hours (24h).
        • Set a custom priority threshold to consider pods for eviction only if their priority is lower than a specified priority level. Use the thresholdPriority field to set a numerical priority threshold or use the thresholdPriorityClassName field to specify a certain priority class name.

          Note

          Do not specify both thresholdPriority and thresholdPriorityClassName for the descheduler.

        • Set specific namespaces to exclude or include from descheduler operations. Expand the namespaces field and add namespaces to the excluded or included list. You can only either set a list of namespaces to exclude or a list of namespaces to include. Note that protected namespaces (openshift-*, kube-system, hypershift) are excluded by default.

          Important

          The LowNodeUtilization strategy does not support namespace exclusion. If the LifecycleAndUtilization profile is set, which enables the LowNodeUtilization strategy, then no namespaces are excluded, even the protected namespaces. To avoid evictions from the protected namespaces while the LowNodeUtilization strategy is enabled, set the priority class name to system-cluster-critical or system-node-critical.

        • Experimental: Set thresholds for underutilization and overutilization for the LowNodeUtilization strategy. Use the devLowNodeUtilizationThresholds field to set one of the following values:

          • Low: 10% underutilized and 30% overutilized
          • Medium: 20% underutilized and 50% overutilized (Default)
          • High: 40% underutilized and 70% overutilized
          Note

          This setting is experimental and should not be used in a production environment.

      4. Optional: Use the Descheduling Interval Seconds field to change the number of seconds between descheduler runs. The default is 3600 seconds.
    4. Click Create.

You can also configure the profiles and settings for the descheduler later using the OpenShift CLI (oc). If you did not adjust the profiles when creating the descheduler instance from the web console, the AffinityAndTaints profile is enabled by default.

4.9.4. Configuring descheduler profiles

You can configure which profiles the descheduler uses to evict pods.

Prerequisites

  • Cluster administrator privileges

Procedure

  1. Edit the KubeDescheduler object:

    $ oc edit kubedeschedulers.operator.openshift.io cluster -n openshift-kube-descheduler-operator
  2. Specify one or more profiles in the spec.profiles section.

    apiVersion: operator.openshift.io/v1
    kind: KubeDescheduler
    metadata:
      name: cluster
      namespace: openshift-kube-descheduler-operator
    spec:
      deschedulingIntervalSeconds: 3600
      logLevel: Normal
      managementState: Managed
      operatorLogLevel: Normal
      mode: Predictive                                     1
      profileCustomizations:
        namespaces:                                        2
          excluded:
          - my-namespace
        podLifetime: 48h                                   3
        thresholdPriorityClassName: my-priority-class-name 4
      profiles:                                            5
      - AffinityAndTaints
      - TopologyAndDuplicates                              6
      - LifecycleAndUtilization
      - EvictPodsWithLocalStorage
      - EvictPodsWithPVC
    1
    Optional: By default, the descheduler does not evict pods. To evict pods, set mode to Automatic.
    2
    Optional: Set a list of user-created namespaces to include or exclude from descheduler operations. Use excluded to set a list of namespaces to exclude or use included to set a list of namespaces to include. Note that protected namespaces (openshift-*, kube-system, hypershift) are excluded by default.
    Important

    The LowNodeUtilization strategy does not support namespace exclusion. If the LifecycleAndUtilization profile is set, which enables the LowNodeUtilization strategy, then no namespaces are excluded, even the protected namespaces. To avoid evictions from the protected namespaces while the LowNodeUtilization strategy is enabled, set the priority class name to system-cluster-critical or system-node-critical.

    3
    Optional: Enable a custom pod lifetime value for the LifecycleAndUtilization profile. Valid units are s, m, or h. The default pod lifetime is 24 hours.
    4
    Optional: Specify a priority threshold to consider pods for eviction only if their priority is lower than the specified level. Use the thresholdPriority field to set a numerical priority threshold (for example, 10000) or use the thresholdPriorityClassName field to specify a certain priority class name (for example, my-priority-class-name). If you specify a priority class name, it must already exist or the descheduler will throw an error. Do not set both thresholdPriority and thresholdPriorityClassName.
    5
    Add one or more profiles to enable. Available profiles: AffinityAndTaints, TopologyAndDuplicates, LifecycleAndUtilization, SoftTopologyAndDuplicates, EvictPodsWithLocalStorage, and EvictPodsWithPVC.
    6
    Do not enable both TopologyAndDuplicates and SoftTopologyAndDuplicates. Enabling both results in a conflict.

    You can enable multiple profiles; the order that the profiles are specified in is not important.

  3. Save the file to apply the changes.

4.9.5. Configuring the descheduler interval

You can configure the amount of time between descheduler runs. The default is 3600 seconds (one hour).

Prerequisites

  • Cluster administrator privileges

Procedure

  1. Edit the KubeDescheduler object:

    $ oc edit kubedeschedulers.operator.openshift.io cluster -n openshift-kube-descheduler-operator
  2. Update the deschedulingIntervalSeconds field to the desired value:

    apiVersion: operator.openshift.io/v1
    kind: KubeDescheduler
    metadata:
      name: cluster
      namespace: openshift-kube-descheduler-operator
    spec:
      deschedulingIntervalSeconds: 3600 1
    ...
    1
    Set the number of seconds between descheduler runs. A value of 0 in this field runs the descheduler once and exits.
  3. Save the file to apply the changes.

4.9.6. Uninstalling the descheduler

You can remove the descheduler from your cluster by removing the descheduler instance and uninstalling the Kube Descheduler Operator. This procedure also cleans up the KubeDescheduler CRD and openshift-kube-descheduler-operator namespace.

Prerequisites

  • Cluster administrator privileges.
  • Access to the OpenShift Container Platform web console.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Delete the descheduler instance.

    1. From the OperatorsInstalled Operators page, click Kube Descheduler Operator.
    2. Select the Kube Descheduler tab.
    3. Click the Options menu kebab next to the cluster entry and select Delete KubeDescheduler.
    4. In the confirmation dialog, click Delete.
  3. Uninstall the Kube Descheduler Operator.

    1. Navigate to OperatorsInstalled Operators.
    2. Click the Options menu kebab next to the Kube Descheduler Operator entry and select Uninstall Operator.
    3. In the confirmation dialog, click Uninstall.
  4. Delete the openshift-kube-descheduler-operator namespace.

    1. Navigate to AdministrationNamespaces.
    2. Enter openshift-kube-descheduler-operator into the filter box.
    3. Click the Options menu kebab next to the openshift-kube-descheduler-operator entry and select Delete Namespace.
    4. In the confirmation dialog, enter openshift-kube-descheduler-operator and click Delete.
  5. Delete the KubeDescheduler CRD.

    1. Navigate to AdministrationCustom Resource Definitions.
    2. Enter KubeDescheduler into the filter box.
    3. Click the Options menu kebab next to the KubeDescheduler entry and select Delete CustomResourceDefinition.
    4. In the confirmation dialog, click Delete.

4.10. Secondary scheduler

4.10.1. Secondary scheduler overview

You can install the Secondary Scheduler Operator to run a custom secondary scheduler alongside the default scheduler to schedule pods.

4.10.1.1. About the Secondary Scheduler Operator

The Secondary Scheduler Operator for Red Hat OpenShift provides a way to deploy a custom secondary scheduler in OpenShift Container Platform. The secondary scheduler runs alongside the default scheduler to schedule pods. Pod configurations can specify which scheduler to use.

The custom scheduler must have the /bin/kube-scheduler binary and be based on the Kubernetes scheduling framework.

Important

You can use the Secondary Scheduler Operator to deploy a custom secondary scheduler in OpenShift Container Platform, but Red Hat does not directly support the functionality of the custom secondary scheduler.

The Secondary Scheduler Operator creates the default roles and role bindings required by the secondary scheduler. You can specify which scheduling plugins to enable or disable by configuring the KubeSchedulerConfiguration resource for the secondary scheduler.

4.10.2. Secondary Scheduler Operator for Red Hat OpenShift release notes

The Secondary Scheduler Operator for Red Hat OpenShift allows you to deploy a custom secondary scheduler in your OpenShift Container Platform cluster.

These release notes track the development of the Secondary Scheduler Operator for Red Hat OpenShift.

For more information, see About the Secondary Scheduler Operator.

4.10.2.1. Release notes for Secondary Scheduler Operator for Red Hat OpenShift 1.1.4

Issued: 26 November 2024

The following advisory is available for the Secondary Scheduler Operator for Red Hat OpenShift 1.1.4:

4.10.2.1.1. Bug fixes
  • This release of the Secondary Scheduler Operator addresses Common Vulnerabilities and Exposures (CVEs).
4.10.2.1.2. Known issues
  • Currently, you cannot deploy additional resources, such as config maps, CRDs, or RBAC policies through the Secondary Scheduler Operator. Any resources other than roles and role bindings that are required by your custom secondary scheduler must be applied externally. (WRKLDS-645)
4.10.2.2. Release notes for Secondary Scheduler Operator for Red Hat OpenShift 1.1.3

Issued: 26 October 2023

The following advisory is available for the Secondary Scheduler Operator for Red Hat OpenShift 1.1.3:

4.10.2.2.1. Bug fixes
  • This release of the Secondary Scheduler Operator addresses Common Vulnerabilities and Exposures (CVEs).
4.10.2.2.2. Known issues
  • Currently, you cannot deploy additional resources, such as config maps, CRDs, or RBAC policies through the Secondary Scheduler Operator. Any resources other than roles and role bindings that are required by your custom secondary scheduler must be applied externally. (WRKLDS-645)
4.10.2.3. Release notes for Secondary Scheduler Operator for Red Hat OpenShift 1.1.2

Issued: 23 August 2023

The following advisory is available for the Secondary Scheduler Operator for Red Hat OpenShift 1.1.2:

4.10.2.3.1. Bug fixes
  • This release of the Secondary Scheduler Operator addresses several Common Vulnerabilities and Exposures (CVEs).
4.10.2.3.2. Known issues
  • Currently, you cannot deploy additional resources, such as config maps, CRDs, or RBAC policies through the Secondary Scheduler Operator. Any resources other than roles and role bindings that are required by your custom secondary scheduler must be applied externally. (WRKLDS-645)
4.10.2.4. Release notes for Secondary Scheduler Operator for Red Hat OpenShift 1.1.0

Issued: 1 September 2022

The following advisory is available for the Secondary Scheduler Operator for Red Hat OpenShift 1.1.0:

4.10.2.4.1. New features and enhancements
4.10.2.4.2. Known issues
  • Currently, you cannot deploy additional resources, such as config maps, CRDs, or RBAC policies through the Secondary Scheduler Operator. Any resources other than roles and role bindings that are required by your custom secondary scheduler must be applied externally. (BZ#2071684)

4.10.3. Scheduling pods using a secondary scheduler

You can run a custom secondary scheduler in OpenShift Container Platform by installing the Secondary Scheduler Operator, deploying the secondary scheduler, and setting the secondary scheduler in the pod definition.

4.10.3.1. Installing the Secondary Scheduler Operator

You can use the web console to install the Secondary Scheduler Operator for Red Hat OpenShift.

Prerequisites

  • You have access to the cluster with cluster-admin privileges.
  • You have access to the OpenShift Container Platform web console.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Create the required namespace for the Secondary Scheduler Operator for Red Hat OpenShift.

    1. Navigate to AdministrationNamespaces and click Create Namespace.
    2. Enter openshift-secondary-scheduler-operator in the Name field and click Create.
  3. Install the Secondary Scheduler Operator for Red Hat OpenShift.

    1. Navigate to OperatorsOperatorHub.
    2. Enter Secondary Scheduler Operator for Red Hat OpenShift into the filter box.
    3. Select the Secondary Scheduler Operator for Red Hat OpenShift and click Install.
    4. On the Install Operator page:

      1. The Update channel is set to stable, which installs the latest stable release of the Secondary Scheduler Operator for Red Hat OpenShift.
      2. Select A specific namespace on the cluster and select openshift-secondary-scheduler-operator from the drop-down menu.
      3. Select an Update approval strategy.

        • The Automatic strategy allows Operator Lifecycle Manager (OLM) to automatically update the Operator when a new version is available.
        • The Manual strategy requires a user with appropriate credentials to approve the Operator update.
      4. Click Install.

Verification

  1. Navigate to OperatorsInstalled Operators.
  2. Verify that Secondary Scheduler Operator for Red Hat OpenShift is listed with a Status of Succeeded.
4.10.3.2. Deploying a secondary scheduler

After you have installed the Secondary Scheduler Operator, you can deploy a secondary scheduler.

Prerequisities

  • You have access to the cluster with cluster-admin privileges.
  • You have access to the OpenShift Container Platform web console.
  • The Secondary Scheduler Operator for Red Hat OpenShift is installed.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Create config map to hold the configuration for the secondary scheduler.

    1. Navigate to WorkloadsConfigMaps.
    2. Click Create ConfigMap.
    3. In the YAML editor, enter the config map definition that contains the necessary KubeSchedulerConfiguration configuration. For example:

      apiVersion: v1
      kind: ConfigMap
      metadata:
        name: "secondary-scheduler-config"                  1
        namespace: "openshift-secondary-scheduler-operator" 2
      data:
        "config.yaml": |
          apiVersion: kubescheduler.config.k8s.io/v1
          kind: KubeSchedulerConfiguration                  3
          leaderElection:
            leaderElect: false
          profiles:
            - schedulerName: secondary-scheduler            4
              plugins:                                      5
                score:
                  disabled:
                    - name: NodeResourcesBalancedAllocation
                    - name: NodeResourcesLeastAllocated
      1
      The name of the config map. This is used in the Scheduler Config field when creating the SecondaryScheduler CR.
      2
      The config map must be created in the openshift-secondary-scheduler-operator namespace.
      3
      The KubeSchedulerConfiguration resource for the secondary scheduler. For more information, see KubeSchedulerConfiguration in the Kubernetes API documentation.
      4
      The name of the secondary scheduler. Pods that set their spec.schedulerName field to this value are scheduled with this secondary scheduler.
      5
      The plugins to enable or disable for the secondary scheduler. For a list default scheduling plugins, see Scheduling plugins in the Kubernetes documentation.
    4. Click Create.
  3. Create the SecondaryScheduler CR:

    1. Navigate to OperatorsInstalled Operators.
    2. Select Secondary Scheduler Operator for Red Hat OpenShift.
    3. Select the Secondary Scheduler tab and click Create SecondaryScheduler.
    4. The Name field defaults to cluster; do not change this name.
    5. The Scheduler Config field defaults to secondary-scheduler-config. Ensure that this value matches the name of the config map created earlier in this procedure.
    6. In the Scheduler Image field, enter the image name for your custom scheduler.

      Important

      Red Hat does not directly support the functionality of your custom secondary scheduler.

    7. Click Create.
4.10.3.3. Scheduling a pod using the secondary scheduler

To schedule a pod using the secondary scheduler, set the schedulerName field in the pod definition.

Prerequisities

  • You have access to the cluster with cluster-admin privileges.
  • You have access to the OpenShift Container Platform web console.
  • The Secondary Scheduler Operator for Red Hat OpenShift is installed.
  • A secondary scheduler is configured.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Navigate to WorkloadsPods.
  3. Click Create Pod.
  4. In the YAML editor, enter the desired pod configuration and add the schedulerName field:

    apiVersion: v1
    kind: Pod
    metadata:
      name: nginx
      namespace: default
    spec:
      containers:
        - name: nginx
          image: nginx:1.14.2
          ports:
            - containerPort: 80
      schedulerName: secondary-scheduler 1
    1
    The schedulerName field must match the name that is defined in the config map when you configured the secondary scheduler.
  5. Click Create.

Verification

  1. Log in to the OpenShift CLI.
  2. Describe the pod using the following command:

    $ oc describe pod nginx -n default

    Example output

    Name:         nginx
    Namespace:    default
    Priority:     0
    Node:         ci-ln-t0w4r1k-72292-xkqs4-worker-b-xqkxp/10.0.128.3
    ...
    Events:
      Type    Reason          Age   From                 Message
      ----    ------          ----  ----                 -------
      Normal  Scheduled       12s   secondary-scheduler  Successfully assigned default/nginx to ci-ln-t0w4r1k-72292-xkqs4-worker-b-xqkxp
    ...

  3. In the events table, find the event with a message similar to Successfully assigned <namespace>/<pod_name> to <node_name>.
  4. In the "From" column, verify that the event was generated from the secondary scheduler and not the default scheduler.

    Note

    You can also check the secondary-scheduler-* pod logs in the openshift-secondary-scheduler-namespace to verify that the pod was scheduled by the secondary scheduler.

4.10.4. Uninstalling the Secondary Scheduler Operator

You can remove the Secondary Scheduler Operator for Red Hat OpenShift from OpenShift Container Platform by uninstalling the Operator and removing its related resources.

4.10.4.1. Uninstalling the Secondary Scheduler Operator

You can uninstall the Secondary Scheduler Operator for Red Hat OpenShift by using the web console.

Prerequisites

  • You have access to the cluster with cluster-admin privileges.
  • You have access to the OpenShift Container Platform web console.
  • The Secondary Scheduler Operator for Red Hat OpenShift is installed.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Uninstall the Secondary Scheduler Operator for Red Hat OpenShift Operator.

    1. Navigate to OperatorsInstalled Operators.
    2. Click the Options menu kebab next to the Secondary Scheduler Operator entry and click Uninstall Operator.
    3. In the confirmation dialog, click Uninstall.
4.10.4.2. Removing Secondary Scheduler Operator resources

Optionally, after uninstalling the Secondary Scheduler Operator for Red Hat OpenShift, you can remove its related resources from your cluster.

Prerequisites

  • You have access to the cluster with cluster-admin privileges.
  • You have access to the OpenShift Container Platform web console.

Procedure

  1. Log in to the OpenShift Container Platform web console.
  2. Remove CRDs that were installed by the Secondary Scheduler Operator:

    1. Navigate to AdministrationCustomResourceDefinitions.
    2. Enter SecondaryScheduler in the Name field to filter the CRDs.
    3. Click the Options menu kebab next to the SecondaryScheduler CRD and select Delete Custom Resource Definition:
  3. Remove the openshift-secondary-scheduler-operator namespace.

    1. Navigate to AdministrationNamespaces.
    2. Click the Options menu kebab next to the openshift-secondary-scheduler-operator and select Delete Namespace.
    3. In the confirmation dialog, enter openshift-secondary-scheduler-operator in the field and click Delete.

Chapter 5. Using Jobs and DaemonSets

5.1. Running background tasks on nodes automatically with daemon sets

As an administrator, you can create and use daemon sets to run replicas of a pod on specific or all nodes in an OpenShift Container Platform cluster.

A daemon set ensures that all (or some) nodes run a copy of a pod. As nodes are added to the cluster, pods are added to the cluster. As nodes are removed from the cluster, those pods are removed through garbage collection. Deleting a daemon set will clean up the pods it created.

You can use daemon sets to create shared storage, run a logging pod on every node in your cluster, or deploy a monitoring agent on every node.

For security reasons, the cluster administrators and the project administrators can create daemon sets.

For more information on daemon sets, see the Kubernetes documentation.

Important

Daemon set scheduling is incompatible with project’s default node selector. If you fail to disable it, the daemon set gets restricted by merging with the default node selector. This results in frequent pod recreates on the nodes that got unselected by the merged node selector, which in turn puts unwanted load on the cluster.

5.1.1. Scheduled by default scheduler

A daemon set ensures that all eligible nodes run a copy of a pod. Normally, the node that a pod runs on is selected by the Kubernetes scheduler. However, daemon set pods are created and scheduled by the daemon set controller. That introduces the following issues:

  • Inconsistent pod behavior: Normal pods waiting to be scheduled are created and in Pending state, but daemon set pods are not created in Pending state. This is confusing to the user.
  • Pod preemption is handled by default scheduler. When preemption is enabled, the daemon set controller will make scheduling decisions without considering pod priority and preemption.

The ScheduleDaemonSetPods feature, enabled by default in OpenShift Container Platform, lets you schedule daemon sets using the default scheduler instead of the daemon set controller, by adding the NodeAffinity term to the daemon set pods, instead of the spec.nodeName term. The default scheduler is then used to bind the pod to the target host. If node affinity of the daemon set pod already exists, it is replaced. The daemon set controller only performs these operations when creating or modifying daemon set pods, and no changes are made to the spec.template of the daemon set.

kind: Pod
apiVersion: v1
metadata:
  name: hello-node-6fbccf8d9-9tmzr
#...
spec:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchFields:
        - key: metadata.name
          operator: In
          values:
          - target-host-name
#...

In addition, a node.kubernetes.io/unschedulable:NoSchedule toleration is added automatically to daemon set pods. The default scheduler ignores unschedulable Nodes when scheduling daemon set pods.

5.1.2. Creating daemonsets

When creating daemon sets, the nodeSelector field is used to indicate the nodes on which the daemon set should deploy replicas.

Prerequisites

  • Before you start using daemon sets, disable the default project-wide node selector in your namespace, by setting the namespace annotation openshift.io/node-selector to an empty string:

    $ oc patch namespace myproject -p \
        '{"metadata": {"annotations": {"openshift.io/node-selector": ""}}}'
    Tip

    You can alternatively apply the following YAML to disable the default project-wide node selector for a namespace:

    apiVersion: v1
    kind: Namespace
    metadata:
      name: <namespace>
      annotations:
        openshift.io/node-selector: ''
    #...
  • If you are creating a new project, overwrite the default node selector:

    $ oc adm new-project <name> --node-selector=""

Procedure

To create a daemon set:

  1. Define the daemon set yaml file:

    apiVersion: apps/v1
    kind: DaemonSet
    metadata:
      name: hello-daemonset
    spec:
      selector:
          matchLabels:
            name: hello-daemonset 1
      template:
        metadata:
          labels:
            name: hello-daemonset 2
        spec:
          nodeSelector: 3
            role: worker
          containers:
          - image: openshift/hello-openshift
            imagePullPolicy: Always
            name: registry
            ports:
            - containerPort: 80
              protocol: TCP
            resources: {}
            terminationMessagePath: /dev/termination-log
          serviceAccount: default
          terminationGracePeriodSeconds: 10
    #...
    1
    The label selector that determines which pods belong to the daemon set.
    2
    The pod template’s label selector. Must match the label selector above.
    3
    The node selector that determines on which nodes pod replicas should be deployed. A matching label must be present on the node.
  2. Create the daemon set object:

    $ oc create -f daemonset.yaml
  3. To verify that the pods were created, and that each node has a pod replica:

    1. Find the daemonset pods:

      $ oc get pods

      Example output

      hello-daemonset-cx6md   1/1       Running   0          2m
      hello-daemonset-e3md9   1/1       Running   0          2m

    2. View the pods to verify the pod has been placed onto the node:

      $ oc describe pod/hello-daemonset-cx6md|grep Node

      Example output

      Node:        openshift-node01.hostname.com/10.14.20.134

      $ oc describe pod/hello-daemonset-e3md9|grep Node

      Example output

      Node:        openshift-node02.hostname.com/10.14.20.137

Important
  • If you update a daemon set pod template, the existing pod replicas are not affected.
  • If you delete a daemon set and then create a new daemon set with a different template but the same label selector, it recognizes any existing pod replicas as having matching labels and thus does not update them or create new replicas despite a mismatch in the pod template.
  • If you change node labels, the daemon set adds pods to nodes that match the new labels and deletes pods from nodes that do not match the new labels.

To update a daemon set, force new pod replicas to be created by deleting the old replicas or nodes.

5.2. Running tasks in pods using jobs

A job executes a task in your OpenShift Container Platform cluster.

A job tracks the overall progress of a task and updates its status with information about active, succeeded, and failed pods. Deleting a job will clean up any pod replicas it created. Jobs are part of the Kubernetes API, which can be managed with oc commands like other object types.

Sample Job specification

apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  parallelism: 1    1
  completions: 1    2
  activeDeadlineSeconds: 1800 3
  backoffLimit: 6   4
  template:         5
    metadata:
      name: pi
    spec:
      containers:
      - name: pi
        image: perl
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: OnFailure    6
#...

1
The pod replicas a job should run in parallel.
2
Successful pod completions are needed to mark a job completed.
3
The maximum duration the job can run.
4
The number of retries for a job.
5
The template for the pod the controller creates.
6
The restart policy of the pod.

Additional resources

  • Jobs in the Kubernetes documentation

5.2.1. Understanding jobs and cron jobs

A job tracks the overall progress of a task and updates its status with information about active, succeeded, and failed pods. Deleting a job cleans up any pods it created. Jobs are part of the Kubernetes API, which can be managed with oc commands like other object types.

There are two possible resource types that allow creating run-once objects in OpenShift Container Platform:

Job

A regular job is a run-once object that creates a task and ensures the job finishes.

There are three main types of task suitable to run as a job:

  • Non-parallel jobs:

    • A job that starts only one pod, unless the pod fails.
    • The job is complete as soon as its pod terminates successfully.
  • Parallel jobs with a fixed completion count:

    • a job that starts multiple pods.
    • The job represents the overall task and is complete when there is one successful pod for each value in the range 1 to the completions value.
  • Parallel jobs with a work queue:

    • A job with multiple parallel worker processes in a given pod.
    • OpenShift Container Platform coordinates pods to determine what each should work on or use an external queue service.
    • Each pod is independently capable of determining whether or not all peer pods are complete and that the entire job is done.
    • When any pod from the job terminates with success, no new pods are created.
    • When at least one pod has terminated with success and all pods are terminated, the job is successfully completed.
    • When any pod has exited with success, no other pod should be doing any work for this task or writing any output. Pods should all be in the process of exiting.

      For more information about how to make use of the different types of job, see Job Patterns in the Kubernetes documentation.

Cron job

A job can be scheduled to run multiple times, using a cron job.

A cron job builds on a regular job by allowing you to specify how the job should be run. Cron jobs are part of the Kubernetes API, which can be managed with oc commands like other object types.

Cron jobs are useful for creating periodic and recurring tasks, like running backups or sending emails. Cron jobs can also schedule individual tasks for a specific time, such as if you want to schedule a job for a low activity period. A cron job creates a Job object based on the timezone configured on the control plane node that runs the cronjob controller.

Warning

A cron job creates a Job object approximately once per execution time of its schedule, but there are circumstances in which it fails to create a job or two jobs might be created. Therefore, jobs must be idempotent and you must configure history limits.

5.2.1.1. Understanding how to create jobs

Both resource types require a job configuration that consists of the following key parts:

  • A pod template, which describes the pod that OpenShift Container Platform creates.
  • The parallelism parameter, which specifies how many pods running in parallel at any point in time should execute a job.

    • For non-parallel jobs, leave unset. When unset, defaults to 1.
  • The completions parameter, specifying how many successful pod completions are needed to finish a job.

    • For non-parallel jobs, leave unset. When unset, defaults to 1.
    • For parallel jobs with a fixed completion count, specify a value.
    • For parallel jobs with a work queue, leave unset. When unset defaults to the parallelism value.
5.2.1.2. Understanding how to set a maximum duration for jobs

When defining a job, you can define its maximum duration by setting the activeDeadlineSeconds field. It is specified in seconds and is not set by default. When not set, there is no maximum duration enforced.

The maximum duration is counted from the time when a first pod gets scheduled in the system, and defines how long a job can be active. It tracks overall time of an execution. After reaching the specified timeout, the job is terminated by OpenShift Container Platform.

5.2.1.3. Understanding how to set a job back off policy for pod failure

A job can be considered failed, after a set amount of retries due to a logical error in configuration or other similar reasons. Failed pods associated with the job are recreated by the controller with an exponential back off delay (10s, 20s, 40s …) capped at six minutes. The limit is reset if no new failed pods appear between controller checks.

Use the spec.backoffLimit parameter to set the number of retries for a job.

5.2.1.4. Understanding how to configure a cron job to remove artifacts

Cron jobs can leave behind artifact resources such as jobs or pods. As a user it is important to configure history limits so that old jobs and their pods are properly cleaned. There are two fields within cron job’s spec responsible for that:

  • .spec.successfulJobsHistoryLimit. The number of successful finished jobs to retain (defaults to 3).
  • .spec.failedJobsHistoryLimit. The number of failed finished jobs to retain (defaults to 1).
Tip
  • Delete cron jobs that you no longer need:

    $ oc delete cronjob/<cron_job_name>

    Doing this prevents them from generating unnecessary artifacts.

  • You can suspend further executions by setting the spec.suspend to true. All subsequent executions are suspended until you reset to false.
5.2.1.5. Known limitations

The job specification restart policy only applies to the pods, and not the job controller. However, the job controller is hard-coded to keep retrying jobs to completion.

As such, restartPolicy: Never or --restart=Never results in the same behavior as restartPolicy: OnFailure or --restart=OnFailure. That is, when a job fails it is restarted automatically until it succeeds (or is manually discarded). The policy only sets which subsystem performs the restart.

With the Never policy, the job controller performs the restart. With each attempt, the job controller increments the number of failures in the job status and create new pods. This means that with each failed attempt, the number of pods increases.

With the OnFailure policy, kubelet performs the restart. Each attempt does not increment the number of failures in the job status. In addition, kubelet will retry failed jobs starting pods on the same nodes.

5.2.2. Creating jobs

You create a job in OpenShift Container Platform by creating a job object.

Procedure

To create a job:

  1. Create a YAML file similar to the following:

    apiVersion: batch/v1
    kind: Job
    metadata:
      name: pi
    spec:
      parallelism: 1    1
      completions: 1    2
      activeDeadlineSeconds: 1800 3
      backoffLimit: 6   4
      template:         5
        metadata:
          name: pi
        spec:
          containers:
          - name: pi
            image: perl
            command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
          restartPolicy: OnFailure    6
    #...
    1
    Optional: Specify how many pod replicas a job should run in parallel; defaults to 1.
    • For non-parallel jobs, leave unset. When unset, defaults to 1.
    2
    Optional: Specify how many successful pod completions are needed to mark a job completed.
    • For non-parallel jobs, leave unset. When unset, defaults to 1.
    • For parallel jobs with a fixed completion count, specify the number of completions.
    • For parallel jobs with a work queue, leave unset. When unset defaults to the parallelism value.
    3
    Optional: Specify the maximum duration the job can run.
    4
    Optional: Specify the number of retries for a job. This field defaults to six.
    5
    Specify the template for the pod the controller creates.
    6
    Specify the restart policy of the pod:
    • Never. Do not restart the job.
    • OnFailure. Restart the job only if it fails.
    • Always. Always restart the job.

      For details on how OpenShift Container Platform uses restart policy with failed containers, see the Example States in the Kubernetes documentation.

  2. Create the job:

    $ oc create -f <file-name>.yaml
Note

You can also create and launch a job from a single command using oc create job. The following command creates and launches a job similar to the one specified in the previous example:

$ oc create job pi --image=perl -- perl -Mbignum=bpi -wle 'print bpi(2000)'

5.2.3. Creating cron jobs

You create a cron job in OpenShift Container Platform by creating a job object.

Procedure

To create a cron job:

  1. Create a YAML file similar to the following:

    apiVersion: batch/v1
    kind: CronJob
    metadata:
      name: pi
    spec:
      schedule: "*/1 * * * *"          1
      timeZone: Etc/UTC                2
      concurrencyPolicy: "Replace"     3
      startingDeadlineSeconds: 200     4
      suspend: true                    5
      successfulJobsHistoryLimit: 3    6
      failedJobsHistoryLimit: 1        7
      jobTemplate:                     8
        spec:
          template:
            metadata:
              labels:                  9
                parent: "cronjobpi"
            spec:
              containers:
              - name: pi
                image: perl
                command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
              restartPolicy: OnFailure 10
    #...
    1
    Schedule for the job specified in cron format. In this example, the job will run every minute.
    2
    An optional time zone for the schedule. See List of tz database time zones for valid options. If not specified, the Kubernetes controller manager interprets the schedule relative to its local time zone. This setting is offered as a Technology Preview.
    3
    An optional concurrency policy, specifying how to treat concurrent jobs within a cron job. Only one of the following concurrent policies may be specified. If not specified, this defaults to allowing concurrent executions.
    • Allow allows cron jobs to run concurrently.
    • Forbid forbids concurrent runs, skipping the next run if the previous has not finished yet.
    • Replace cancels the currently running job and replaces it with a new one.
    4
    An optional deadline (in seconds) for starting the job if it misses its scheduled time for any reason. Missed jobs executions will be counted as failed ones. If not specified, there is no deadline.
    5
    An optional flag allowing the suspension of a cron job. If set to true, all subsequent executions will be suspended.
    6
    The number of successful finished jobs to retain (defaults to 3).
    7
    The number of failed finished jobs to retain (defaults to 1).
    8
    Job template. This is similar to the job example.
    9
    Sets a label for jobs spawned by this cron job.
    10
    The restart policy of the pod. This does not apply to the job controller.
    Note

    The .spec.successfulJobsHistoryLimit and .spec.failedJobsHistoryLimit fields are optional. These fields specify how many completed and failed jobs should be kept. By default, they are set to 3 and 1 respectively. Setting a limit to 0 corresponds to keeping none of the corresponding kind of jobs after they finish.

  2. Create the cron job:

    $ oc create -f <file-name>.yaml
Note

You can also create and launch a cron job from a single command using oc create cronjob. The following command creates and launches a cron job similar to the one specified in the previous example:

$ oc create cronjob pi --image=perl --schedule='*/1 * * * *' -- perl -Mbignum=bpi -wle 'print bpi(2000)'

With oc create cronjob, the --schedule option accepts schedules in cron format.

Chapter 6. Working with nodes

6.1. Viewing and listing the nodes in your OpenShift Container Platform cluster

You can list all the nodes in your cluster to obtain information such as status, age, memory usage, and details about the nodes.

When you perform node management operations, the CLI interacts with node objects that are representations of actual node hosts. The master uses the information from node objects to validate nodes with health checks.

6.1.1. About listing all the nodes in a cluster

You can get detailed information on the nodes in the cluster.

  • The following command lists all nodes:

    $ oc get nodes

    The following example is a cluster with healthy nodes:

    $ oc get nodes

    Example output

    NAME                   STATUS    ROLES     AGE       VERSION
    master.example.com     Ready     master    7h        v1.25.0
    node1.example.com      Ready     worker    7h        v1.25.0
    node2.example.com      Ready     worker    7h        v1.25.0

    The following example is a cluster with one unhealthy node:

    $ oc get nodes

    Example output

    NAME                   STATUS                      ROLES     AGE       VERSION
    master.example.com     Ready                       master    7h        v1.25.0
    node1.example.com      NotReady,SchedulingDisabled worker    7h        v1.25.0
    node2.example.com      Ready                       worker    7h        v1.25.0

    The conditions that trigger a NotReady status are shown later in this section.

  • The -o wide option provides additional information on nodes.

    $ oc get nodes -o wide

    Example output

    NAME                STATUS   ROLES    AGE    VERSION   INTERNAL-IP    EXTERNAL-IP   OS-IMAGE                                                       KERNEL-VERSION                 CONTAINER-RUNTIME
    master.example.com  Ready    master   171m   v1.25.0   10.0.129.108   <none>        Red Hat Enterprise Linux CoreOS 48.83.202103210901-0 (Ootpa)   4.18.0-240.15.1.el8_3.x86_64   cri-o://1.25.0-30.rhaos4.10.gitf2f339d.el8-dev
    node1.example.com   Ready    worker   72m    v1.25.0   10.0.129.222   <none>        Red Hat Enterprise Linux CoreOS 48.83.202103210901-0 (Ootpa)   4.18.0-240.15.1.el8_3.x86_64   cri-o://1.25.0-30.rhaos4.10.gitf2f339d.el8-dev
    node2.example.com   Ready    worker   164m   v1.25.0   10.0.142.150   <none>        Red Hat Enterprise Linux CoreOS 48.83.202103210901-0 (Ootpa)   4.18.0-240.15.1.el8_3.x86_64   cri-o://1.25.0-30.rhaos4.10.gitf2f339d.el8-dev

  • The following command lists information about a single node:

    $ oc get node <node>

    For example:

    $ oc get node node1.example.com

    Example output

    NAME                   STATUS    ROLES     AGE       VERSION
    node1.example.com      Ready     worker    7h        v1.25.0

  • The following command provides more detailed information about a specific node, including the reason for the current condition:

    $ oc describe node <node>

    For example:

    $ oc describe node node1.example.com

    Example output

    Name:               node1.example.com 1
    Roles:              worker 2
    Labels:             beta.kubernetes.io/arch=amd64   3
                        beta.kubernetes.io/instance-type=m4.large
                        beta.kubernetes.io/os=linux
                        failure-domain.beta.kubernetes.io/region=us-east-2
                        failure-domain.beta.kubernetes.io/zone=us-east-2a
                        kubernetes.io/hostname=ip-10-0-140-16
                        node-role.kubernetes.io/worker=
    Annotations:        cluster.k8s.io/machine: openshift-machine-api/ahardin-worker-us-east-2a-q5dzc  4
                        machineconfiguration.openshift.io/currentConfig: worker-309c228e8b3a92e2235edd544c62fea8
                        machineconfiguration.openshift.io/desiredConfig: worker-309c228e8b3a92e2235edd544c62fea8
                        machineconfiguration.openshift.io/state: Done
                        volumes.kubernetes.io/controller-managed-attach-detach: true
    CreationTimestamp:  Wed, 13 Feb 2019 11:05:57 -0500
    Taints:             <none>  5
    Unschedulable:      false
    Conditions:                 6
      Type             Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
      ----             ------  -----------------                 ------------------                ------                       -------
      OutOfDisk        False   Wed, 13 Feb 2019 15:09:42 -0500   Wed, 13 Feb 2019 11:05:57 -0500   KubeletHasSufficientDisk     kubelet has sufficient disk space available
      MemoryPressure   False   Wed, 13 Feb 2019 15:09:42 -0500   Wed, 13 Feb 2019 11:05:57 -0500   KubeletHasSufficientMemory   kubelet has sufficient memory available
      DiskPressure     False   Wed, 13 Feb 2019 15:09:42 -0500   Wed, 13 Feb 2019 11:05:57 -0500   KubeletHasNoDiskPressure     kubelet has no disk pressure
      PIDPressure      False   Wed, 13 Feb 2019 15:09:42 -0500   Wed, 13 Feb 2019 11:05:57 -0500   KubeletHasSufficientPID      kubelet has sufficient PID available
      Ready            True    Wed, 13 Feb 2019 15:09:42 -0500   Wed, 13 Feb 2019 11:07:09 -0500   KubeletReady                 kubelet is posting ready status
    Addresses:   7
      InternalIP:   10.0.140.16
      InternalDNS:  ip-10-0-140-16.us-east-2.compute.internal
      Hostname:     ip-10-0-140-16.us-east-2.compute.internal
    Capacity:    8
     attachable-volumes-aws-ebs:  39
     cpu:                         2
     hugepages-1Gi:               0
     hugepages-2Mi:               0
     memory:                      8172516Ki
     pods:                        250
    Allocatable:
     attachable-volumes-aws-ebs:  39
     cpu:                         1500m
     hugepages-1Gi:               0
     hugepages-2Mi:               0
     memory:                      7558116Ki
     pods:                        250
    System Info:    9
     Machine ID:                              63787c9534c24fde9a0cde35c13f1f66
     System UUID:                             EC22BF97-A006-4A58-6AF8-0A38DEEA122A
     Boot ID:                                 f24ad37d-2594-46b4-8830-7f7555918325
     Kernel Version:                          3.10.0-957.5.1.el7.x86_64
     OS Image:                                Red Hat Enterprise Linux CoreOS 410.8.20190520.0 (Ootpa)
     Operating System:                        linux
     Architecture:                            amd64
     Container Runtime Version:               cri-o://1.25.0-0.6.dev.rhaos4.3.git9ad059b.el8-rc2
     Kubelet Version:                         v1.25.0
     Kube-Proxy Version:                      v1.25.0
    PodCIDR:                                  10.128.4.0/24
    ProviderID:                               aws:///us-east-2a/i-04e87b31dc6b3e171
    Non-terminated Pods:                      (12 in total)  10
      Namespace                               Name                                   CPU Requests  CPU Limits  Memory Requests  Memory Limits
      ---------                               ----                                   ------------  ----------  ---------------  -------------
      openshift-cluster-node-tuning-operator  tuned-hdl5q                            0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-dns                           dns-default-l69zr                      0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-image-registry                node-ca-9hmcg                          0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-ingress                       router-default-76455c45c-c5ptv         0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-machine-config-operator       machine-config-daemon-cvqw9            20m (1%)      0 (0%)      50Mi (0%)        0 (0%)
      openshift-marketplace                   community-operators-f67fh              0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-monitoring                    alertmanager-main-0                    50m (3%)      50m (3%)    210Mi (2%)       10Mi (0%)
      openshift-monitoring                    node-exporter-l7q8d                    10m (0%)      20m (1%)    20Mi (0%)        40Mi (0%)
      openshift-monitoring                    prometheus-adapter-75d769c874-hvb85    0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-multus                        multus-kw8w5                           0 (0%)        0 (0%)      0 (0%)           0 (0%)
      openshift-sdn                           ovs-t4dsn                              100m (6%)     0 (0%)      300Mi (4%)       0 (0%)
      openshift-sdn                           sdn-g79hg                              100m (6%)     0 (0%)      200Mi (2%)       0 (0%)
    Allocated resources:
      (Total limits may be over 100 percent, i.e., overcommitted.)
      Resource                    Requests     Limits
      --------                    --------     ------
      cpu                         380m (25%)   270m (18%)
      memory                      880Mi (11%)  250Mi (3%)
      attachable-volumes-aws-ebs  0            0
    Events:     11
      Type     Reason                   Age                From                      Message
      ----     ------                   ----               ----                      -------
      Normal   NodeHasSufficientPID     6d (x5 over 6d)    kubelet, m01.example.com  Node m01.example.com status is now: NodeHasSufficientPID
      Normal   NodeAllocatableEnforced  6d                 kubelet, m01.example.com  Updated Node Allocatable limit across pods
      Normal   NodeHasSufficientMemory  6d (x6 over 6d)    kubelet, m01.example.com  Node m01.example.com status is now: NodeHasSufficientMemory
      Normal   NodeHasNoDiskPressure    6d (x6 over 6d)    kubelet, m01.example.com  Node m01.example.com status is now: NodeHasNoDiskPressure
      Normal   NodeHasSufficientDisk    6d (x6 over 6d)    kubelet, m01.example.com  Node m01.example.com status is now: NodeHasSufficientDisk
      Normal   NodeHasSufficientPID     6d                 kubelet, m01.example.com  Node m01.example.com status is now: NodeHasSufficientPID
      Normal   Starting                 6d                 kubelet, m01.example.com  Starting kubelet.
    #...

    1
    The name of the node.
    2
    The role of the node, either master or worker.
    3
    The labels applied to the node.
    4
    The annotations applied to the node.
    5
    The taints applied to the node.
    6
    The node conditions and status. The conditions stanza lists the Ready, PIDPressure, MemoryPressure, DiskPressure and OutOfDisk status. These condition are described later in this section.
    7
    The IP address and hostname of the node.
    8
    The pod resources and allocatable resources.
    9
    Information about the node host.
    10
    The pods on the node.
    11
    The events reported by the node.
Note

The control plane label is not automatically added to newly created or updated master nodes. If you want to use the control plane label for your nodes, you can manually configure the label. For more information, see Understanding how to update labels on nodes in the Additional resources section.

Among the information shown for nodes, the following node conditions appear in the output of the commands shown in this section:

Table 6.1. Node Conditions
ConditionDescription

Ready

If true, the node is healthy and ready to accept pods. If false, the node is not healthy and is not accepting pods. If unknown, the node controller has not received a heartbeat from the node for the node-monitor-grace-period (the default is 40 seconds).

DiskPressure

If true, the disk capacity is low.

MemoryPressure

If true, the node memory is low.

PIDPressure

If true, there are too many processes on the node.

OutOfDisk

If true, the node has insufficient free space on the node for adding new pods.

NetworkUnavailable

If true, the network for the node is not correctly configured.

NotReady

If true, one of the underlying components, such as the container runtime or network, is experiencing issues or is not yet configured.

SchedulingDisabled

Pods cannot be scheduled for placement on the node.

6.1.2. Listing pods on a node in your cluster

You can list all the pods on a specific node.

Procedure

  • To list all or selected pods on one or more nodes:

    $ oc describe node <node1> <node2>

    For example:

    $ oc describe node ip-10-0-128-218.ec2.internal
  • To list all or selected pods on selected nodes:

    $ oc describe node --selector=<node_selector>
    $ oc describe node --selector=kubernetes.io/os

    Or:

    $ oc describe node -l=<pod_selector>
    $ oc describe node -l node-role.kubernetes.io/worker
  • To list all pods on a specific node, including terminated pods:

    $ oc get pod --all-namespaces --field-selector=spec.nodeName=<nodename>

6.1.3. Viewing memory and CPU usage statistics on your nodes

You can display usage statistics about nodes, which provide the runtime environments for containers. These usage statistics include CPU, memory, and storage consumption.

Prerequisites

  • You must have cluster-reader permission to view the usage statistics.
  • Metrics must be installed to view the usage statistics.

Procedure

  • To view the usage statistics:

    $ oc adm top nodes

    Example output

    NAME                                   CPU(cores)   CPU%      MEMORY(bytes)   MEMORY%
    ip-10-0-12-143.ec2.compute.internal    1503m        100%      4533Mi          61%
    ip-10-0-132-16.ec2.compute.internal    76m          5%        1391Mi          18%
    ip-10-0-140-137.ec2.compute.internal   398m         26%       2473Mi          33%
    ip-10-0-142-44.ec2.compute.internal    656m         43%       6119Mi          82%
    ip-10-0-146-165.ec2.compute.internal   188m         12%       3367Mi          45%
    ip-10-0-19-62.ec2.compute.internal     896m         59%       5754Mi          77%
    ip-10-0-44-193.ec2.compute.internal    632m         42%       5349Mi          72%

  • To view the usage statistics for nodes with labels:

    $ oc adm top node --selector=''

    You must choose the selector (label query) to filter on. Supports =, ==, and !=.

6.2. Working with nodes

As an administrator, you can perform several tasks to make your clusters more efficient.

6.2.1. Understanding how to evacuate pods on nodes

Evacuating pods allows you to migrate all or selected pods from a given node or nodes.

You can only evacuate pods backed by a replication controller. The replication controller creates new pods on other nodes and removes the existing pods from the specified node(s).

Bare pods, meaning those not backed by a replication controller, are unaffected by default. You can evacuate a subset of pods by specifying a pod-selector. Pod selectors are based on labels, so all the pods with the specified label will be evacuated.

Procedure

  1. Mark the nodes unschedulable before performing the pod evacuation.

    1. Mark the node as unschedulable:

      $ oc adm cordon <node1>

      Example output

      node/<node1> cordoned

    2. Check that the node status is Ready,SchedulingDisabled:

      $ oc get node <node1>

      Example output

      NAME        STATUS                     ROLES     AGE       VERSION
      <node1>     Ready,SchedulingDisabled   worker    1d        v1.25.0

  2. Evacuate the pods using one of the following methods:

    • Evacuate all or selected pods on one or more nodes:

      $ oc adm drain <node1> <node2> [--pod-selector=<pod_selector>]
    • Force the deletion of bare pods using the --force option. When set to true, deletion continues even if there are pods not managed by a replication controller, replica set, job, daemon set, or stateful set:

      $ oc adm drain <node1> <node2> --force=true
    • Set a period of time in seconds for each pod to terminate gracefully, use --grace-period. If negative, the default value specified in the pod will be used:

      $ oc adm drain <node1> <node2> --grace-period=-1
    • Ignore pods managed by daemon sets using the --ignore-daemonsets flag set to true:

      $ oc adm drain <node1> <node2> --ignore-daemonsets=true
    • Set the length of time to wait before giving up using the --timeout flag. A value of 0 sets an infinite length of time:

      $ oc adm drain <node1> <node2> --timeout=5s
    • Delete pods even if there are pods using emptyDir volumes by setting the --delete-emptydir-data flag to true. Local data is deleted when the node is drained:

      $ oc adm drain <node1> <node2> --delete-emptydir-data=true
    • List objects that will be migrated without actually performing the evacuation, using the --dry-run option set to true:

      $ oc adm drain <node1> <node2>  --dry-run=true

      Instead of specifying specific node names (for example, <node1> <node2>), you can use the --selector=<node_selector> option to evacuate pods on selected nodes.

  3. Mark the node as schedulable when done.

    $ oc adm uncordon <node1>

6.2.2. Understanding how to update labels on nodes

You can update any label on a node.

Node labels are not persisted after a node is deleted even if the node is backed up by a Machine.

Note

Any change to a MachineSet object is not applied to existing machines owned by the compute machine set. For example, labels edited or added to an existing MachineSet object are not propagated to existing machines and nodes associated with the compute machine set.

  • The following command adds or updates labels on a node:

    $ oc label node <node> <key_1>=<value_1> ... <key_n>=<value_n>

    For example:

    $ oc label nodes webconsole-7f7f6 unhealthy=true
    Tip

    You can alternatively apply the following YAML to apply the label:

    kind: Node
    apiVersion: v1
    metadata:
      name: webconsole-7f7f6
      labels:
        unhealthy: 'true'
    #...
  • The following command updates all pods in the namespace:

    $ oc label pods --all <key_1>=<value_1>

    For example:

    $ oc label pods --all status=unhealthy

6.2.3. Understanding how to mark nodes as unschedulable or schedulable

By default, healthy nodes with a Ready status are marked as schedulable, which means that you can place new pods on the node. Manually marking a node as unschedulable blocks any new pods from being scheduled on the node. Existing pods on the node are not affected.

  • The following command marks a node or nodes as unschedulable:

    Example output

    $ oc adm cordon <node>

    For example:

    $ oc adm cordon node1.example.com

    Example output

    node/node1.example.com cordoned
    
    NAME                 LABELS                                        STATUS
    node1.example.com    kubernetes.io/hostname=node1.example.com      Ready,SchedulingDisabled

  • The following command marks a currently unschedulable node or nodes as schedulable:

    $ oc adm uncordon <node1>

    Alternatively, instead of specifying specific node names (for example, <node>), you can use the --selector=<node_selector> option to mark selected nodes as schedulable or unschedulable.

6.2.4. Handling errors in single-node OpenShift clusters when the node reboots without draining application pods

In single-node OpenShift clusters and in OpenShift Container Platform clusters in general, a situation can arise where a node reboot occurs without first draining the node. This can occur where an application pod requesting devices fails with the UnexpectedAdmissionError error. Deployment, ReplicaSet, or DaemonSet errors are reported because the application pods that require those devices start before the pod serving those devices. You cannot control the order of pod restarts.

While this behavior is to be expected, it can cause a pod to remain on the cluster even though it has failed to deploy successfully. The pod continues to report UnexpectedAdmissionError. This issue is mitigated by the fact that application pods are typically included in a Deployment, ReplicaSet, or DaemonSet. If a pod is in this error state, it is of little concern because another instance should be running. Belonging to a Deployment, ReplicaSet, or DaemonSet guarantees the successful creation and execution of subsequent pods and ensures the successful deployment of the application.

There is ongoing work upstream to ensure that such pods are gracefully terminated. Until that work is resolved, run the following command for a single-node OpenShift cluster to remove the failed pods:

$ oc delete pods --field-selector status.phase=Failed -n <POD_NAMESPACE>
Note

The option to drain the node is unavailable for single-node OpenShift clusters.

6.2.5. Deleting nodes

6.2.5.1. Deleting nodes from a cluster

To delete a node from the OpenShift Container Platform cluster, scale down the appropriate MachineSet object.

Important

When a cluster is integrated with a cloud provider, you must delete the corresponding machine to delete a node. Do not try to use the oc delete node command for this task.

When you delete a node by using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node are not deleted. Any bare pods that are not backed by a replication controller become inaccessible to OpenShift Container Platform. Pods backed by replication controllers are rescheduled to other available nodes. You must delete local manifest pods.

Note

If you are running cluster on bare metal, you cannot delete a node by editing MachineSet objects. Compute machine sets are only available when a cluster is integrated with a cloud provider. Instead you must unschedule and drain the node before manually deleting it.

Procedure

  1. View the compute machine sets that are in the cluster by running the following command:

    $ oc get machinesets -n openshift-machine-api

    The compute machine sets are listed in the form of <cluster-id>-worker-<aws-region-az>.

  2. Scale down the compute machine set by using one of the following methods:

    • Specify the number of replicas to scale down to by running the following command:

      $ oc scale --replicas=2 machineset <machine-set-name> -n openshift-machine-api
    • Edit the compute machine set custom resource by running the following command:

      $ oc edit machineset <machine-set-name> -n openshift-machine-api

      Example output

      apiVersion: machine.openshift.io/v1beta1
      kind: MachineSet
      metadata:
        # ...
        name: <machine-set-name>
        namespace: openshift-machine-api
        # ...
      spec:
        replicas: 2 1
        # ...

      1
      Specify the number of replicas to scale down to.
6.2.5.2. Deleting nodes from a bare metal cluster

When you delete a node using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node are not deleted. Any bare pods not backed by a replication controller become inaccessible to OpenShift Container Platform. Pods backed by replication controllers are rescheduled to other available nodes. You must delete local manifest pods.

Procedure

Delete a node from an OpenShift Container Platform cluster running on bare metal by completing the following steps:

  1. Mark the node as unschedulable:

    $ oc adm cordon <node_name>
  2. Drain all pods on the node:

    $ oc adm drain <node_name> --force=true

    This step might fail if the node is offline or unresponsive. Even if the node does not respond, it might still be running a workload that writes to shared storage. To avoid data corruption, power down the physical hardware before you proceed.

  3. Delete the node from the cluster:

    $ oc delete node <node_name>

    Although the node object is now deleted from the cluster, it can still rejoin the cluster after reboot or if the kubelet service is restarted. To permanently delete the node and all its data, you must decommission the node.

  4. If you powered down the physical hardware, turn it back on so that the node can rejoin the cluster.

6.3. Managing nodes

OpenShift Container Platform uses a KubeletConfig custom resource (CR) to manage the configuration of nodes. By creating an instance of a KubeletConfig object, a managed machine config is created to override setting on the node.

Note

Logging in to remote machines for the purpose of changing their configuration is not supported.

6.3.1. Modifying nodes

To make configuration changes to a cluster, or machine pool, you must create a custom resource definition (CRD), or kubeletConfig object. OpenShift Container Platform uses the Machine Config Controller to watch for changes introduced through the CRD to apply the changes to the cluster.

Note

Because the fields in a kubeletConfig object are passed directly to the kubelet from upstream Kubernetes, the validation of those fields is handled directly by the kubelet itself. Please refer to the relevant Kubernetes documentation for the valid values for these fields. Invalid values in the kubeletConfig object can render cluster nodes unusable.

Procedure

  1. Obtain the label associated with the static CRD, Machine Config Pool, for the type of node you want to configure. Perform one of the following steps:

    1. Check current labels of the desired machine config pool.

      For example:

      $  oc get machineconfigpool  --show-labels

      Example output

      NAME      CONFIG                                             UPDATED   UPDATING   DEGRADED   LABELS
      master    rendered-master-e05b81f5ca4db1d249a1bf32f9ec24fd   True      False      False      operator.machineconfiguration.openshift.io/required-for-upgrade=
      worker    rendered-worker-f50e78e1bc06d8e82327763145bfcf62   True      False      False

    2. Add a custom label to the desired machine config pool.

      For example:

      $ oc label machineconfigpool worker custom-kubelet=enabled
  2. Create a kubeletconfig custom resource (CR) for your configuration change.

    For example:

    Sample configuration for a custom-config CR

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: custom-config 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
          custom-kubelet: enabled 2
      kubeletConfig: 3
        podsPerCore: 10
        maxPods: 250
        systemReserved:
          cpu: 2000m
          memory: 1Gi
    #...

    1
    Assign a name to CR.
    2
    Specify the label to apply the configuration change, this is the label you added to the machine config pool.
    3
    Specify the new value(s) you want to change.
  3. Create the CR object.

    $ oc create -f <file-name>

    For example:

    $ oc create -f master-kube-config.yaml

Most Kubelet Configuration options can be set by the user. The following options are not allowed to be overwritten:

  • CgroupDriver
  • ClusterDNS
  • ClusterDomain
  • StaticPodPath
Note

If a single node contains more than 50 images, pod scheduling might be imbalanced across nodes. This is because the list of images on a node is shortened to 50 by default. You can disable the image limit by editing the KubeletConfig object and setting the value of nodeStatusMaxImages to -1.

6.3.2. Configuring control plane nodes as schedulable

You can configure control plane nodes to be schedulable, meaning that new pods are allowed for placement on the master nodes. By default, control plane nodes are not schedulable.

You can set the masters to be schedulable, but must retain the worker nodes.

Note

You can deploy OpenShift Container Platform with no worker nodes on a bare metal cluster. In this case, the control plane nodes are marked schedulable by default.

You can allow or disallow control plane nodes to be schedulable by configuring the mastersSchedulable field.

Important

When you configure control plane nodes from the default unschedulable to schedulable, additional subscriptions are required. This is because control plane nodes then become worker nodes.

Procedure

  1. Edit the schedulers.config.openshift.io resource.

    $ oc edit schedulers.config.openshift.io cluster
  2. Configure the mastersSchedulable field.

    apiVersion: config.openshift.io/v1
    kind: Scheduler
    metadata:
      creationTimestamp: "2019-09-10T03:04:05Z"
      generation: 1
      name: cluster
      resourceVersion: "433"
      selfLink: /apis/config.openshift.io/v1/schedulers/cluster
      uid: a636d30a-d377-11e9-88d4-0a60097bee62
    spec:
      mastersSchedulable: false 1
    status: {}
    #...
    1
    Set to true to allow control plane nodes to be schedulable, or false to disallow control plane nodes to be schedulable.
  3. Save the file to apply the changes.

6.3.3. Setting SELinux booleans

OpenShift Container Platform allows you to enable and disable an SELinux boolean on a Red Hat Enterprise Linux CoreOS (RHCOS) node. The following procedure explains how to modify SELinux booleans on nodes using the Machine Config Operator (MCO). This procedure uses container_manage_cgroup as the example boolean. You can modify this value to whichever boolean you need.

Prerequisites

  • You have installed the OpenShift CLI (oc).

Procedure

  1. Create a new YAML file with a MachineConfig object, displayed in the following example:

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfig
    metadata:
      labels:
        machineconfiguration.openshift.io/role: worker
      name: 99-worker-setsebool
    spec:
      config:
        ignition:
          version: 3.2.0
        systemd:
          units:
          - contents: |
              [Unit]
              Description=Set SELinux booleans
              Before=kubelet.service
    
              [Service]
              Type=oneshot
              ExecStart=/sbin/setsebool container_manage_cgroup=on
              RemainAfterExit=true
    
              [Install]
              WantedBy=multi-user.target graphical.target
            enabled: true
            name: setsebool.service
    #...
  2. Create the new MachineConfig object by running the following command:

    $ oc create -f 99-worker-setsebool.yaml
Note

Applying any changes to the MachineConfig object causes all affected nodes to gracefully reboot after the change is applied.

6.3.4. Adding kernel arguments to nodes

In some special cases, you might want to add kernel arguments to a set of nodes in your cluster. This should only be done with caution and clear understanding of the implications of the arguments you set.

Warning

Improper use of kernel arguments can result in your systems becoming unbootable.

Examples of kernel arguments you could set include:

  • nosmt: Disables symmetric multithreading (SMT) in the kernel. Multithreading allows multiple logical threads for each CPU. You could consider nosmt in multi-tenant environments to reduce risks from potential cross-thread attacks. By disabling SMT, you essentially choose security over performance.
  • systemd.unified_cgroup_hierarchy: Enables Linux control group version 2 (cgroup v2). cgroup v2 is the next version of the kernel control group and offers multiple improvements.

    Important

    OpenShift Container Platform cgroups version 2 support is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

    For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

  • enforcing=0: Configures Security Enhanced Linux (SELinux) to run in permissive mode. In permissive mode, the system acts as if SELinux is enforcing the loaded security policy, including labeling objects and emitting access denial entries in the logs, but it does not actually deny any operations. While not supported for production systems, permissive mode can be helpful for debugging.

    Warning

    Disabling SELinux on RHCOS in production is not supported. Once SELinux has been disabled on a node, it must be re-provisioned before re-inclusion in a production cluster.

See Kernel.org kernel parameters for a list and descriptions of kernel arguments.

In the following procedure, you create a MachineConfig object that identifies:

  • A set of machines to which you want to add the kernel argument. In this case, machines with a worker role.
  • Kernel arguments that are appended to the end of the existing kernel arguments.
  • A label that indicates where in the list of machine configs the change is applied.

Prerequisites

  • Have administrative privilege to a working OpenShift Container Platform cluster.

Procedure

  1. List existing MachineConfig objects for your OpenShift Container Platform cluster to determine how to label your machine config:

    $ oc get MachineConfig

    Example output

    NAME                                               GENERATEDBYCONTROLLER                      IGNITIONVERSION   AGE
    00-master                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    00-worker                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-master-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-master-ssh                                                                                 3.2.0             40m
    99-worker-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-worker-ssh                                                                                 3.2.0             40m
    rendered-master-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m

  2. Create a MachineConfig object file that identifies the kernel argument (for example, 05-worker-kernelarg-selinuxpermissive.yaml)

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfig
    metadata:
      labels:
        machineconfiguration.openshift.io/role: worker1
      name: 05-worker-kernelarg-selinuxpermissive2
    spec:
      kernelArguments:
        - enforcing=03
    1
    Applies the new kernel argument only to worker nodes.
    2
    Named to identify where it fits among the machine configs (05) and what it does (adds a kernel argument to configure SELinux permissive mode).
    3
    Identifies the exact kernel argument as enforcing=0.
  3. Create the new machine config:

    $ oc create -f 05-worker-kernelarg-selinuxpermissive.yaml
  4. Check the machine configs to see that the new one was added:

    $ oc get MachineConfig

    Example output

    NAME                                               GENERATEDBYCONTROLLER                      IGNITIONVERSION   AGE
    00-master                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    00-worker                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    05-worker-kernelarg-selinuxpermissive                                                         3.2.0             105s
    99-master-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-master-ssh                                                                                 3.2.0             40m
    99-worker-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-worker-ssh                                                                                 3.2.0             40m
    rendered-master-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m

  5. Check the nodes:

    $ oc get nodes

    Example output

    NAME                           STATUS                     ROLES    AGE   VERSION
    ip-10-0-136-161.ec2.internal   Ready                      worker   28m   v1.25.0
    ip-10-0-136-243.ec2.internal   Ready                      master   34m   v1.25.0
    ip-10-0-141-105.ec2.internal   Ready,SchedulingDisabled   worker   28m   v1.25.0
    ip-10-0-142-249.ec2.internal   Ready                      master   34m   v1.25.0
    ip-10-0-153-11.ec2.internal    Ready                      worker   28m   v1.25.0
    ip-10-0-153-150.ec2.internal   Ready                      master   34m   v1.25.0

    You can see that scheduling on each worker node is disabled as the change is being applied.

  6. Check that the kernel argument worked by going to one of the worker nodes and listing the kernel command line arguments (in /proc/cmdline on the host):

    $ oc debug node/ip-10-0-141-105.ec2.internal

    Example output

    Starting pod/ip-10-0-141-105ec2internal-debug ...
    To use host binaries, run `chroot /host`
    
    sh-4.2# cat /host/proc/cmdline
    BOOT_IMAGE=/ostree/rhcos-... console=tty0 console=ttyS0,115200n8
    rootflags=defaults,prjquota rw root=UUID=fd0... ostree=/ostree/boot.0/rhcos/16...
    coreos.oem.id=qemu coreos.oem.id=ec2 ignition.platform.id=ec2 enforcing=0
    
    sh-4.2# exit

    You should see the enforcing=0 argument added to the other kernel arguments.

6.3.5. Enabling swap memory use on nodes

Important

Enabling swap memory use on nodes is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

You can enable swap memory use for OpenShift Container Platform workloads on a per-node basis.

Warning

Enabling swap memory can negatively impact workload performance and out-of-resource handling. Do not enable swap memory on control plane nodes.

To enable swap memory, create a kubeletconfig custom resource (CR) to set the swapbehavior parameter. You can set limited or unlimited swap memory:

  • Limited: Use the LimitedSwap value to limit how much swap memory workloads can use. Any workloads on the node that are not managed by OpenShift Container Platform can still use swap memory. The LimitedSwap behavior depends on whether the node is running with Linux control groups version 1 (cgroups v1) or version 2 (cgroup v2):

    • cgroup v1: OpenShift Container Platform workloads can use any combination of memory and swap, up to the pod’s memory limit, if set.
    • cgroup v2: OpenShift Container Platform workloads cannot use swap memory.
  • Unlimited: Use the UnlimitedSwap value to allow workloads to use as much swap memory as they request, up to the system limit.

Because the kubelet will not start in the presence of swap memory without this configuration, you must enable swap memory in OpenShift Container Platform before enabling swap memory on the nodes. If there is no swap memory present on a node, enabling swap memory in OpenShift Container Platform has no effect.

Prerequisites

  • You have a running OpenShift Container Platform cluster that uses version 4.10 or later.
  • You are logged in to the cluster as a user with administrative privileges.
  • You have enabled the TechPreviewNoUpgrade feature set on the cluster (see Nodes → Working with clusters → Enabling features using feature gates).

    Note

    Enabling the TechPreviewNoUpgrade feature set cannot be undone and prevents minor version updates. These feature sets are not recommended on production clusters.

  • If cgroup v2 is enabled on a node, you must enable swap accounting on the node, by setting the swapaccount=1 kernel argument.

Procedure

  1. Apply a custom label to the machine config pool where you want to allow swap memory.

    $ oc label machineconfigpool worker kubelet-swap=enabled
  2. Create a custom resource (CR) to enable and configure swap settings.

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: swap-config
    spec:
      machineConfigPoolSelector:
        matchLabels:
          kubelet-swap: enabled
      kubeletConfig:
        failSwapOn: false 1
        memorySwap:
          swapBehavior: LimitedSwap 2
    #...
    1
    Set to false to enable swap memory use on the associated nodes. Set to true to disable swap memory use.
    2
    Specify the swap memory behavior. If unspecified, the default is LimitedSwap.
  3. Enable swap memory on the machines.

6.3.6. Migrating control plane nodes from one RHOSP host to another

You can run a script that moves a control plane node from one Red Hat OpenStack Platform (RHOSP) node to another.

Prerequisites

  • The environment variable OS_CLOUD refers to a clouds entry that has administrative credentials in a clouds.yaml file.
  • The environment variable KUBECONFIG refers to a configuration that contains administrative OpenShift Container Platform credentials.

Procedure

  • From a command line, run the following script:
#!/usr/bin/env bash

set -Eeuo pipefail

if [ $# -lt 1 ]; then
	echo "Usage: '$0 node_name'"
	exit 64
fi

# Check for admin OpenStack credentials
openstack server list --all-projects >/dev/null || { >&2 echo "The script needs OpenStack admin credentials. Exiting"; exit 77; }

# Check for admin OpenShift credentials
oc adm top node >/dev/null || { >&2 echo "The script needs OpenShift admin credentials. Exiting"; exit 77; }

set -x

declare -r node_name="$1"
declare server_id
server_id="$(openstack server list --all-projects -f value -c ID -c Name | grep "$node_name" | cut -d' ' -f1)"
readonly server_id

# Drain the node
oc adm cordon "$node_name"
oc adm drain "$node_name" --delete-emptydir-data --ignore-daemonsets --force

# Power off the server
oc debug "node/${node_name}" -- chroot /host shutdown -h 1

# Verify the server is shut off
until openstack server show "$server_id" -f value -c status | grep -q 'SHUTOFF'; do sleep 5; done

# Migrate the node
openstack server migrate --wait "$server_id"

# Resize the VM
openstack server resize confirm "$server_id"

# Wait for the resize confirm to finish
until openstack server show "$server_id" -f value -c status | grep -q 'SHUTOFF'; do sleep 5; done

# Restart the VM
openstack server start "$server_id"

# Wait for the node to show up as Ready:
until oc get node "$node_name" | grep -q "^${node_name}[[:space:]]\+Ready"; do sleep 5; done

# Uncordon the node
oc adm uncordon "$node_name"

# Wait for cluster operators to stabilize
until oc get co -o go-template='statuses: {{ range .items }}{{ range .status.conditions }}{{ if eq .type "Degraded" }}{{ if ne .status "False" }}DEGRADED{{ end }}{{ else if eq .type "Progressing"}}{{ if ne .status "False" }}PROGRESSING{{ end }}{{ else if eq .type "Available"}}{{ if ne .status "True" }}NOTAVAILABLE{{ end }}{{ end }}{{ end }}{{ end }}' | grep -qv '\(DEGRADED\|PROGRESSING\|NOTAVAILABLE\)'; do sleep 5; done

If the script completes, the control plane machine is migrated to a new RHOSP node.

6.4. Managing the maximum number of pods per node

In OpenShift Container Platform, you can configure the number of pods that can run on a node based on the number of processor cores on the node, a hard limit or both. If you use both options, the lower of the two limits the number of pods on a node.

When both options are in use, the lower of the two values limits the number of pods on a node. Exceeding these values can result in:

  • Increased CPU utilization.
  • Slow pod scheduling.
  • Potential out-of-memory scenarios, depending on the amount of memory in the node.
  • Exhausting the pool of IP addresses.
  • Resource overcommitting, leading to poor user application performance.
Important

In Kubernetes, a pod that is holding a single container actually uses two containers. The second container is used to set up networking prior to the actual container starting. Therefore, a system running 10 pods will actually have 20 containers running.

Note

Disk IOPS throttling from the cloud provider might have an impact on CRI-O and kubelet. They might get overloaded when there are large number of I/O intensive pods running on the nodes. It is recommended that you monitor the disk I/O on the nodes and use volumes with sufficient throughput for the workload.

The podsPerCore parameter sets the number of pods the node can run based on the number of processor cores on the node. For example, if podsPerCore is set to 10 on a node with 4 processor cores, the maximum number of pods allowed on the node will be 40.

kubeletConfig:
  podsPerCore: 10

Setting podsPerCore to 0 disables this limit. The default is 0. The value of the podsPerCore parameter cannot exceed the value of the maxPods parameter.

The maxPods parameter sets the number of pods the node can run to a fixed value, regardless of the properties of the node.

 kubeletConfig:
    maxPods: 250

6.4.1. Configuring the maximum number of pods per node

Two parameters control the maximum number of pods that can be scheduled to a node: podsPerCore and maxPods. If you use both options, the lower of the two limits the number of pods on a node.

For example, if podsPerCore is set to 10 on a node with 4 processor cores, the maximum number of pods allowed on the node will be 40.

Prerequisites

  1. Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command:

    $ oc edit machineconfigpool <name>

    For example:

    $ oc edit machineconfigpool worker

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfigPool
    metadata:
      creationTimestamp: "2022-11-16T15:34:25Z"
      generation: 4
      labels:
        pools.operator.machineconfiguration.openshift.io/worker: "" 1
      name: worker
    #...

    1
    The label appears under Labels.
    Tip

    If the label is not present, add a key/value pair such as:

    $ oc label machineconfigpool worker custom-kubelet=small-pods

Procedure

  1. Create a custom resource (CR) for your configuration change.

    Sample configuration for a max-pods CR

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: set-max-pods 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 2
      kubeletConfig:
        podsPerCore: 10 3
        maxPods: 250 4
    #...

    1
    Assign a name to CR.
    2
    Specify the label from the machine config pool.
    3
    Specify the number of pods the node can run based on the number of processor cores on the node.
    4
    Specify the number of pods the node can run to a fixed value, regardless of the properties of the node.
    Note

    Setting podsPerCore to 0 disables this limit.

    In the above example, the default value for podsPerCore is 10 and the default value for maxPods is 250. This means that unless the node has 25 cores or more, by default, podsPerCore will be the limiting factor.

  2. Run the following command to create the CR:

    $ oc create -f <file_name>.yaml

Verification

  1. List the MachineConfigPool CRDs to see if the change is applied. The UPDATING column reports True if the change is picked up by the Machine Config Controller:

    $ oc get machineconfigpools

    Example output

    NAME     CONFIG                        UPDATED   UPDATING   DEGRADED
    master   master-9cc2c72f205e103bb534   False     False      False
    worker   worker-8cecd1236b33ee3f8a5e   False     True       False

    Once the change is complete, the UPDATED column reports True.

    $ oc get machineconfigpools

    Example output

    NAME     CONFIG                        UPDATED   UPDATING   DEGRADED
    master   master-9cc2c72f205e103bb534   False     True       False
    worker   worker-8cecd1236b33ee3f8a5e   True      False      False

6.5. Using the Node Tuning Operator

Learn about the Node Tuning Operator and how you can use it to manage node-level tuning by orchestrating the tuned daemon.

The Node Tuning Operator helps you manage node-level tuning by orchestrating the TuneD daemon and achieves low latency performance by using the Performance Profile controller. The majority of high-performance applications require some level of kernel tuning. The Node Tuning Operator provides a unified management interface to users of node-level sysctls and more flexibility to add custom tuning specified by user needs.

The Operator manages the containerized TuneD daemon for OpenShift Container Platform as a Kubernetes daemon set. It ensures the custom tuning specification is passed to all containerized TuneD daemons running in the cluster in the format that the daemons understand. The daemons run on all nodes in the cluster, one per node.

Node-level settings applied by the containerized TuneD daemon are rolled back on an event that triggers a profile change or when the containerized TuneD daemon is terminated gracefully by receiving and handling a termination signal.

The Node Tuning Operator uses the Performance Profile controller to implement automatic tuning to achieve low latency performance for OpenShift Container Platform applications. The cluster administrator configures a performance profile to define node-level settings such as the following:

  • Updating the kernel to kernel-rt.
  • Choosing CPUs for housekeeping.
  • Choosing CPUs for running workloads.
Note

Currently, disabling CPU load balancing is not supported by cgroup v2. As a result, you might not get the desired behavior from performance profiles if you have cgroup v2 enabled. Enabling cgroup v2 is not recommended if you are using performance profiles.

The Node Tuning Operator is part of a standard OpenShift Container Platform installation in version 4.1 and later.

Note

In earlier versions of OpenShift Container Platform, the Performance Addon Operator was used to implement automatic tuning to achieve low latency performance for OpenShift applications. In OpenShift Container Platform 4.11 and later, this functionality is part of the Node Tuning Operator.

6.5.1. Accessing an example Node Tuning Operator specification

Use this process to access an example Node Tuning Operator specification.

Procedure

  • Run the following command to access an example Node Tuning Operator specification:

    oc get tuned.tuned.openshift.io/default -o yaml -n openshift-cluster-node-tuning-operator

The default CR is meant for delivering standard node-level tuning for the OpenShift Container Platform platform and it can only be modified to set the Operator Management state. Any other custom changes to the default CR will be overwritten by the Operator. For custom tuning, create your own Tuned CRs. Newly created CRs will be combined with the default CR and custom tuning applied to OpenShift Container Platform nodes based on node or pod labels and profile priorities.

Warning

While in certain situations the support for pod labels can be a convenient way of automatically delivering required tuning, this practice is discouraged and strongly advised against, especially in large-scale clusters. The default Tuned CR ships without pod label matching. If a custom profile is created with pod label matching, then the functionality will be enabled at that time. The pod label functionality will be deprecated in future versions of the Node Tuning Operator.

6.5.2. Custom tuning specification

The custom resource (CR) for the Operator has two major sections. The first section, profile:, is a list of TuneD profiles and their names. The second, recommend:, defines the profile selection logic.

Multiple custom tuning specifications can co-exist as multiple CRs in the Operator’s namespace. The existence of new CRs or the deletion of old CRs is detected by the Operator. All existing custom tuning specifications are merged and appropriate objects for the containerized TuneD daemons are updated.

Management state

The Operator Management state is set by adjusting the default Tuned CR. By default, the Operator is in the Managed state and the spec.managementState field is not present in the default Tuned CR. Valid values for the Operator Management state are as follows:

  • Managed: the Operator will update its operands as configuration resources are updated
  • Unmanaged: the Operator will ignore changes to the configuration resources
  • Removed: the Operator will remove its operands and resources the Operator provisioned

Profile data

The profile: section lists TuneD profiles and their names.

profile:
- name: tuned_profile_1
  data: |
    # TuneD profile specification
    [main]
    summary=Description of tuned_profile_1 profile

    [sysctl]
    net.ipv4.ip_forward=1
    # ... other sysctl's or other TuneD daemon plugins supported by the containerized TuneD

# ...

- name: tuned_profile_n
  data: |
    # TuneD profile specification
    [main]
    summary=Description of tuned_profile_n profile

    # tuned_profile_n profile settings

Recommended profiles

The profile: selection logic is defined by the recommend: section of the CR. The recommend: section is a list of items to recommend the profiles based on a selection criteria.

recommend:
<recommend-item-1>
# ...
<recommend-item-n>

The individual items of the list:

- machineConfigLabels: 1
    <mcLabels> 2
  match: 3
    <match> 4
  priority: <priority> 5
  profile: <tuned_profile_name> 6
  operand: 7
    debug: <bool> 8
    tunedConfig:
      reapply_sysctl: <bool> 9
1
Optional.
2
A dictionary of key/value MachineConfig labels. The keys must be unique.
3
If omitted, profile match is assumed unless a profile with a higher priority matches first or machineConfigLabels is set.
4
An optional list.
5
Profile ordering priority. Lower numbers mean higher priority (0 is the highest priority).
6
A TuneD profile to apply on a match. For example tuned_profile_1.
7
Optional operand configuration.
8
Turn debugging on or off for the TuneD daemon. Options are true for on or false for off. The default is false.
9
Turn reapply_sysctl functionality on or off for the TuneD daemon. Options are true for on and false for off.

<match> is an optional list recursively defined as follows:

- label: <label_name> 1
  value: <label_value> 2
  type: <label_type> 3
    <match> 4
1
Node or pod label name.
2
Optional node or pod label value. If omitted, the presence of <label_name> is enough to match.
3
Optional object type (node or pod). If omitted, node is assumed.
4
An optional <match> list.

If <match> is not omitted, all nested <match> sections must also evaluate to true. Otherwise, false is assumed and the profile with the respective <match> section will not be applied or recommended. Therefore, the nesting (child <match> sections) works as logical AND operator. Conversely, if any item of the <match> list matches, the entire <match> list evaluates to true. Therefore, the list acts as logical OR operator.

If machineConfigLabels is defined, machine config pool based matching is turned on for the given recommend: list item. <mcLabels> specifies the labels for a machine config. The machine config is created automatically to apply host settings, such as kernel boot parameters, for the profile <tuned_profile_name>. This involves finding all machine config pools with machine config selector matching <mcLabels> and setting the profile <tuned_profile_name> on all nodes that are assigned the found machine config pools. To target nodes that have both master and worker roles, you must use the master role.

The list items match and machineConfigLabels are connected by the logical OR operator. The match item is evaluated first in a short-circuit manner. Therefore, if it evaluates to true, the machineConfigLabels item is not considered.

Important

When using machine config pool based matching, it is advised to group nodes with the same hardware configuration into the same machine config pool. Not following this practice might result in TuneD operands calculating conflicting kernel parameters for two or more nodes sharing the same machine config pool.

Example: node or pod label based matching

- match:
  - label: tuned.openshift.io/elasticsearch
    match:
    - label: node-role.kubernetes.io/master
    - label: node-role.kubernetes.io/infra
    type: pod
  priority: 10
  profile: openshift-control-plane-es
- match:
  - label: node-role.kubernetes.io/master
  - label: node-role.kubernetes.io/infra
  priority: 20
  profile: openshift-control-plane
- priority: 30
  profile: openshift-node

The CR above is translated for the containerized TuneD daemon into its recommend.conf file based on the profile priorities. The profile with the highest priority (10) is openshift-control-plane-es and, therefore, it is considered first. The containerized TuneD daemon running on a given node looks to see if there is a pod running on the same node with the tuned.openshift.io/elasticsearch label set. If not, the entire <match> section evaluates as false. If there is such a pod with the label, in order for the <match> section to evaluate to true, the node label also needs to be node-role.kubernetes.io/master or node-role.kubernetes.io/infra.

If the labels for the profile with priority 10 matched, openshift-control-plane-es profile is applied and no other profile is considered. If the node/pod label combination did not match, the second highest priority profile (openshift-control-plane) is considered. This profile is applied if the containerized TuneD pod runs on a node with labels node-role.kubernetes.io/master or node-role.kubernetes.io/infra.

Finally, the profile openshift-node has the lowest priority of 30. It lacks the <match> section and, therefore, will always match. It acts as a profile catch-all to set openshift-node profile, if no other profile with higher priority matches on a given node.

Decision workflow

Example: machine config pool based matching

apiVersion: tuned.openshift.io/v1
kind: Tuned
metadata:
  name: openshift-node-custom
  namespace: openshift-cluster-node-tuning-operator
spec:
  profile:
  - data: |
      [main]
      summary=Custom OpenShift node profile with an additional kernel parameter
      include=openshift-node
      [bootloader]
      cmdline_openshift_node_custom=+skew_tick=1
    name: openshift-node-custom

  recommend:
  - machineConfigLabels:
      machineconfiguration.openshift.io/role: "worker-custom"
    priority: 20
    profile: openshift-node-custom

To minimize node reboots, label the target nodes with a label the machine config pool’s node selector will match, then create the Tuned CR above and finally create the custom machine config pool itself.

Cloud provider-specific TuneD profiles

With this functionality, all Cloud provider-specific nodes can conveniently be assigned a TuneD profile specifically tailored to a given Cloud provider on a OpenShift Container Platform cluster. This can be accomplished without adding additional node labels or grouping nodes into machine config pools.

This functionality takes advantage of spec.providerID node object values in the form of <cloud-provider>://<cloud-provider-specific-id> and writes the file /var/lib/tuned/provider with the value <cloud-provider> in NTO operand containers. The content of this file is then used by TuneD to load provider-<cloud-provider> profile if such profile exists.

The openshift profile that both openshift-control-plane and openshift-node profiles inherit settings from is now updated to use this functionality through the use of conditional profile loading. Neither NTO nor TuneD currently ship any Cloud provider-specific profiles. However, it is possible to create a custom profile provider-<cloud-provider> that will be applied to all Cloud provider-specific cluster nodes.

Example GCE Cloud provider profile

apiVersion: tuned.openshift.io/v1
kind: Tuned
metadata:
  name: provider-gce
  namespace: openshift-cluster-node-tuning-operator
spec:
  profile:
  - data: |
      [main]
      summary=GCE Cloud provider-specific profile
      # Your tuning for GCE Cloud provider goes here.
    name: provider-gce

Note

Due to profile inheritance, any setting specified in the provider-<cloud-provider> profile will be overwritten by the openshift profile and its child profiles.

6.5.3. Default profiles set on a cluster

The following are the default profiles set on a cluster.

apiVersion: tuned.openshift.io/v1
kind: Tuned
metadata:
  name: default
  namespace: openshift-cluster-node-tuning-operator
spec:
  profile:
  - data: |
      [main]
      summary=Optimize systems running OpenShift (provider specific parent profile)
      include=-provider-${f:exec:cat:/var/lib/tuned/provider},openshift
    name: openshift
  recommend:
  - profile: openshift-control-plane
    priority: 30
    match:
    - label: node-role.kubernetes.io/master
    - label: node-role.kubernetes.io/infra
  - profile: openshift-node
    priority: 40

Starting with OpenShift Container Platform 4.9, all OpenShift TuneD profiles are shipped with the TuneD package. You can use the oc exec command to view the contents of these profiles:

$ oc exec $tuned_pod -n openshift-cluster-node-tuning-operator -- find /usr/lib/tuned/openshift{,-control-plane,-node} -name tuned.conf -exec grep -H ^ {} \;

6.5.4. Supported TuneD daemon plugins

Excluding the [main] section, the following TuneD plugins are supported when using custom profiles defined in the profile: section of the Tuned CR:

  • audio
  • cpu
  • disk
  • eeepc_she
  • modules
  • mounts
  • net
  • scheduler
  • scsi_host
  • selinux
  • sysctl
  • sysfs
  • usb
  • video
  • vm
  • bootloader

There is some dynamic tuning functionality provided by some of these plugins that is not supported. The following TuneD plugins are currently not supported:

  • script
  • systemd
Note

The TuneD bootloader plugin only supports Red Hat Enterprise Linux CoreOS (RHCOS) worker nodes.

6.6. Remediating, fencing, and maintaining nodes

When node-level failures occur, such as the kernel hangs or network interface controllers (NICs) fail, the work required from the cluster does not decrease, and workloads from affected nodes need to be restarted somewhere. Failures affecting these workloads risk data loss, corruption, or both. It is important to isolate the node, known as fencing, before initiating recovery of the workload, known as remediation, and recovery of the node.

For more information on remediation, fencing, and maintaining nodes, see the Workload Availability for Red Hat OpenShift documentation.

6.7. Understanding node rebooting

To reboot a node without causing an outage for applications running on the platform, it is important to first evacuate the pods. For pods that are made highly available by the routing tier, nothing else needs to be done. For other pods needing storage, typically databases, it is critical to ensure that they can remain in operation with one pod temporarily going offline. While implementing resiliency for stateful pods is different for each application, in all cases it is important to configure the scheduler to use node anti-affinity to ensure that the pods are properly spread across available nodes.

Another challenge is how to handle nodes that are running critical infrastructure such as the router or the registry. The same node evacuation process applies, though it is important to understand certain edge cases.

6.7.1. About rebooting nodes running critical infrastructure

When rebooting nodes that host critical OpenShift Container Platform infrastructure components, such as router pods, registry pods, and monitoring pods, ensure that there are at least three nodes available to run these components.

The following scenario demonstrates how service interruptions can occur with applications running on OpenShift Container Platform when only two nodes are available:

  • Node A is marked unschedulable and all pods are evacuated.
  • The registry pod running on that node is now redeployed on node B. Node B is now running both registry pods.
  • Node B is now marked unschedulable and is evacuated.
  • The service exposing the two pod endpoints on node B loses all endpoints, for a brief period of time, until they are redeployed to node A.

When using three nodes for infrastructure components, this process does not result in a service disruption. However, due to pod scheduling, the last node that is evacuated and brought back into rotation does not have a registry pod. One of the other nodes has two registry pods. To schedule the third registry pod on the last node, use pod anti-affinity to prevent the scheduler from locating two registry pods on the same node.

Additional information

6.7.2. Rebooting a node using pod anti-affinity

Pod anti-affinity is slightly different than node anti-affinity. Node anti-affinity can be violated if there are no other suitable locations to deploy a pod. Pod anti-affinity can be set to either required or preferred.

With this in place, if only two infrastructure nodes are available and one is rebooted, the container image registry pod is prevented from running on the other node. oc get pods reports the pod as unready until a suitable node is available. Once a node is available and all pods are back in ready state, the next node can be restarted.

Procedure

To reboot a node using pod anti-affinity:

  1. Edit the node specification to configure pod anti-affinity:

    apiVersion: v1
    kind: Pod
    metadata:
      name: with-pod-antiaffinity
    spec:
      affinity:
        podAntiAffinity: 1
          preferredDuringSchedulingIgnoredDuringExecution: 2
          - weight: 100 3
            podAffinityTerm:
              labelSelector:
                matchExpressions:
                - key: registry 4
                  operator: In 5
                  values:
                  - default
              topologyKey: kubernetes.io/hostname
    #...
    1
    Stanza to configure pod anti-affinity.
    2
    Defines a preferred rule.
    3
    Specifies a weight for a preferred rule. The node with the highest weight is preferred.
    4
    Description of the pod label that determines when the anti-affinity rule applies. Specify a key and value for the label.
    5
    The operator represents the relationship between the label on the existing pod and the set of values in the matchExpression parameters in the specification for the new pod. Can be In, NotIn, Exists, or DoesNotExist.

    This example assumes the container image registry pod has a label of registry=default. Pod anti-affinity can use any Kubernetes match expression.

  2. Enable the MatchInterPodAffinity scheduler predicate in the scheduling policy file.
  3. Perform a graceful restart of the node.

6.7.3. Understanding how to reboot nodes running routers

In most cases, a pod running an OpenShift Container Platform router exposes a host port.

The PodFitsPorts scheduler predicate ensures that no router pods using the same port can run on the same node, and pod anti-affinity is achieved. If the routers are relying on IP failover for high availability, there is nothing else that is needed.

For router pods relying on an external service such as AWS Elastic Load Balancing for high availability, it is that service’s responsibility to react to router pod restarts.

In rare cases, a router pod may not have a host port configured. In those cases, it is important to follow the recommended restart process for infrastructure nodes.

6.7.4. Rebooting a node gracefully

Before rebooting a node, it is recommended to backup etcd data to avoid any data loss on the node.

Note

For single-node OpenShift clusters that require users to perform the oc login command rather than having the certificates in kubeconfig file to manage the cluster, the oc adm commands might not be available after cordoning and draining the node. This is because the openshift-oauth-apiserver pod is not running due to the cordon. You can use SSH to access the nodes as indicated in the following procedure.

In a single-node OpenShift cluster, pods cannot be rescheduled when cordoning and draining. However, doing so gives the pods, especially your workload pods, time to properly stop and release associated resources.

Procedure

To perform a graceful restart of a node:

  1. Mark the node as unschedulable:

    $ oc adm cordon <node1>
  2. Drain the node to remove all the running pods:

    $ oc adm drain <node1> --ignore-daemonsets --delete-emptydir-data --force

    You might receive errors that pods associated with custom pod disruption budgets (PDB) cannot be evicted.

    Example error

    error when evicting pods/"rails-postgresql-example-1-72v2w" -n "rails" (will retry after 5s): Cannot evict pod as it would violate the pod's disruption budget.

    In this case, run the drain command again, adding the disable-eviction flag, which bypasses the PDB checks:

    $ oc adm drain <node1> --ignore-daemonsets --delete-emptydir-data --force --disable-eviction
  3. Access the node in debug mode:

    $ oc debug node/<node1>
  4. Change your root directory to /host:

    $ chroot /host
  5. Restart the node:

    $ systemctl reboot

    In a moment, the node enters the NotReady state.

    Note

    With some single-node OpenShift clusters, the oc commands might not be available after you cordon and drain the node because the openshift-oauth-apiserver pod is not running. You can use SSH to connect to the node and perform the reboot.

    $ ssh core@<master-node>.<cluster_name>.<base_domain>
    $ sudo systemctl reboot
  6. After the reboot is complete, mark the node as schedulable by running the following command:

    $ oc adm uncordon <node1>
    Note

    With some single-node OpenShift clusters, the oc commands might not be available after you cordon and drain the node because the openshift-oauth-apiserver pod is not running. You can use SSH to connect to the node and uncordon it.

    $ ssh core@<target_node>
    $ sudo oc adm uncordon <node> --kubeconfig /etc/kubernetes/static-pod-resources/kube-apiserver-certs/secrets/node-kubeconfigs/localhost.kubeconfig
  7. Verify that the node is ready:

    $ oc get node <node1>

    Example output

    NAME    STATUS  ROLES    AGE     VERSION
    <node1> Ready   worker   6d22h   v1.18.3+b0068a8

Additional information

For information on etcd data backup, see Backing up etcd data.

6.8. Freeing node resources using garbage collection

As an administrator, you can use OpenShift Container Platform to ensure that your nodes are running efficiently by freeing up resources through garbage collection.

The OpenShift Container Platform node performs two types of garbage collection:

  • Container garbage collection: Removes terminated containers.
  • Image garbage collection: Removes images not referenced by any running pods.

6.8.1. Understanding how terminated containers are removed through garbage collection

Container garbage collection removes terminated containers by using eviction thresholds.

When eviction thresholds are set for garbage collection, the node tries to keep any container for any pod accessible from the API. If the pod has been deleted, the containers will be as well. Containers are preserved as long the pod is not deleted and the eviction threshold is not reached. If the node is under disk pressure, it will remove containers and their logs will no longer be accessible using oc logs.

  • eviction-soft - A soft eviction threshold pairs an eviction threshold with a required administrator-specified grace period.
  • eviction-hard - A hard eviction threshold has no grace period, and if observed, OpenShift Container Platform takes immediate action.

The following table lists the eviction thresholds:

Table 6.2. Variables for configuring container garbage collection
Node conditionEviction signalDescription

MemoryPressure

memory.available

The available memory on the node.

DiskPressure

  • nodefs.available
  • nodefs.inodesFree
  • imagefs.available
  • imagefs.inodesFree

The available disk space or inodes on the node root file system, nodefs, or image file system, imagefs.

Note

For evictionHard you must specify all of these parameters. If you do not specify all parameters, only the specified parameters are applied and the garbage collection will not function properly.

If a node is oscillating above and below a soft eviction threshold, but not exceeding its associated grace period, the corresponding node would constantly oscillate between true and false. As a consequence, the scheduler could make poor scheduling decisions.

To protect against this oscillation, use the eviction-pressure-transition-period flag to control how long OpenShift Container Platform must wait before transitioning out of a pressure condition. OpenShift Container Platform will not set an eviction threshold as being met for the specified pressure condition for the period specified before toggling the condition back to false.

6.8.2. Understanding how images are removed through garbage collection

Image garbage collection removes images that are not referenced by any running pods.

OpenShift Container Platform determines which images to remove from a node based on the disk usage that is reported by cAdvisor.

The policy for image garbage collection is based on two conditions:

  • The percent of disk usage (expressed as an integer) which triggers image garbage collection. The default is 85.
  • The percent of disk usage (expressed as an integer) to which image garbage collection attempts to free. Default is 80.

For image garbage collection, you can modify any of the following variables using a custom resource.

Table 6.3. Variables for configuring image garbage collection
SettingDescription

imageMinimumGCAge

The minimum age for an unused image before the image is removed by garbage collection. The default is 2m.

imageGCHighThresholdPercent

The percent of disk usage, expressed as an integer, which triggers image garbage collection. The default is 85.

imageGCLowThresholdPercent

The percent of disk usage, expressed as an integer, to which image garbage collection attempts to free. The default is 80.

Two lists of images are retrieved in each garbage collector run:

  1. A list of images currently running in at least one pod.
  2. A list of images available on a host.

As new containers are run, new images appear. All images are marked with a time stamp. If the image is running (the first list above) or is newly detected (the second list above), it is marked with the current time. The remaining images are already marked from the previous spins. All images are then sorted by the time stamp.

Once the collection starts, the oldest images get deleted first until the stopping criterion is met.

6.8.3. Configuring garbage collection for containers and images

As an administrator, you can configure how OpenShift Container Platform performs garbage collection by creating a kubeletConfig object for each machine config pool.

Note

OpenShift Container Platform supports only one kubeletConfig object for each machine config pool.

You can configure any combination of the following:

  • Soft eviction for containers
  • Hard eviction for containers
  • Eviction for images

Container garbage collection removes terminated containers. Image garbage collection removes images that are not referenced by any running pods.

Prerequisites

  1. Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command:

    $ oc edit machineconfigpool <name>

    For example:

    $ oc edit machineconfigpool worker

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfigPool
    metadata:
      creationTimestamp: "2022-11-16T15:34:25Z"
      generation: 4
      labels:
        pools.operator.machineconfiguration.openshift.io/worker: "" 1
      name: worker
    #...

    1
    The label appears under Labels.
    Tip

    If the label is not present, add a key/value pair such as:

    $ oc label machineconfigpool worker custom-kubelet=small-pods

Procedure

  1. Create a custom resource (CR) for your configuration change.

    Important

    If there is one file system, or if /var/lib/kubelet and /var/lib/containers/ are in the same file system, the settings with the highest values trigger evictions, as those are met first. The file system triggers the eviction.

    Sample configuration for a container garbage collection CR:

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: worker-kubeconfig 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 2
      kubeletConfig:
        evictionSoft: 3
          memory.available: "500Mi" 4
          nodefs.available: "10%"
          nodefs.inodesFree: "5%"
          imagefs.available: "15%"
          imagefs.inodesFree: "10%"
        evictionSoftGracePeriod:  5
          memory.available: "1m30s"
          nodefs.available: "1m30s"
          nodefs.inodesFree: "1m30s"
          imagefs.available: "1m30s"
          imagefs.inodesFree: "1m30s"
        evictionHard: 6
          memory.available: "200Mi"
          nodefs.available: "5%"
          nodefs.inodesFree: "4%"
          imagefs.available: "10%"
          imagefs.inodesFree: "5%"
        evictionPressureTransitionPeriod: 0s 7
        imageMinimumGCAge: 5m 8
        imageGCHighThresholdPercent: 80 9
        imageGCLowThresholdPercent: 75 10
    #...

    1
    Name for the object.
    2
    Specify the label from the machine config pool.
    3
    For container garbage collection: Type of eviction: evictionSoft or evictionHard.
    4
    For container garbage collection: Eviction thresholds based on a specific eviction trigger signal.
    5
    For container garbage collection: Grace periods for the soft eviction. This parameter does not apply to eviction-hard.
    6
    For container garbage collection: Eviction thresholds based on a specific eviction trigger signal. For evictionHard you must specify all of these parameters. If you do not specify all parameters, only the specified parameters are applied and the garbage collection will not function properly.
    7
    For container garbage collection: The duration to wait before transitioning out of an eviction pressure condition.
    8
    For image garbage collection: The minimum age for an unused image before the image is removed by garbage collection.
    9
    For image garbage collection: The percent of disk usage (expressed as an integer) that triggers image garbage collection.
    10
    For image garbage collection: The percent of disk usage (expressed as an integer) that image garbage collection attempts to free.
  2. Run the following command to create the CR:

    $ oc create -f <file_name>.yaml

    For example:

    $ oc create -f gc-container.yaml

    Example output

    kubeletconfig.machineconfiguration.openshift.io/gc-container created

Verification

  1. Verify that garbage collection is active by entering the following command. The Machine Config Pool you specified in the custom resource appears with UPDATING as 'true` until the change is fully implemented:

    $ oc get machineconfigpool

    Example output

    NAME     CONFIG                                   UPDATED   UPDATING
    master   rendered-master-546383f80705bd5aeaba93   True      False
    worker   rendered-worker-b4c51bb33ccaae6fc4a6a5   False     True

6.9. Allocating resources for nodes in an OpenShift Container Platform cluster

To provide more reliable scheduling and minimize node resource overcommitment, reserve a portion of the CPU and memory resources for use by the underlying node components, such as kubelet and kube-proxy, and the remaining system components, such as sshd and NetworkManager. By specifying the resources to reserve, you provide the scheduler with more information about the remaining CPU and memory resources that a node has available for use by pods. You can allow OpenShift Container Platform to automatically determine the optimal system-reserved CPU and memory resources for your nodes or you can manually determine and set the best resources for your nodes.

Important

To manually set resource values, you must use a kubelet config CR. You cannot use a machine config CR.

6.9.1. Understanding how to allocate resources for nodes

CPU and memory resources reserved for node components in OpenShift Container Platform are based on two node settings:

SettingDescription

kube-reserved

This setting is not used with OpenShift Container Platform. Add the CPU and memory resources that you planned to reserve to the system-reserved setting.

system-reserved

This setting identifies the resources to reserve for the node components and system components, such as CRI-O and Kubelet. The default settings depend on the OpenShift Container Platform and Machine Config Operator versions. Confirm the default systemReserved parameter on the machine-config-operator repository.

If a flag is not set, the defaults are used. If none of the flags are set, the allocated resource is set to the node’s capacity as it was before the introduction of allocatable resources.

Note

Any CPUs specifically reserved using the reservedSystemCPUs parameter are not available for allocation using kube-reserved or system-reserved.

6.9.1.1. How OpenShift Container Platform computes allocated resources

An allocated amount of a resource is computed based on the following formula:

[Allocatable] = [Node Capacity] - [system-reserved] - [Hard-Eviction-Thresholds]
Note

The withholding of Hard-Eviction-Thresholds from Allocatable improves system reliability because the value for Allocatable is enforced for pods at the node level.

If Allocatable is negative, it is set to 0.

Each node reports the system resources that are used by the container runtime and kubelet. To simplify configuring the system-reserved parameter, view the resource use for the node by using the node summary API. The node summary is available at /api/v1/nodes/<node>/proxy/stats/summary.

6.9.1.2. How nodes enforce resource constraints

The node is able to limit the total amount of resources that pods can consume based on the configured allocatable value. This feature significantly improves the reliability of the node by preventing pods from using CPU and memory resources that are needed by system services such as the container runtime and node agent. To improve node reliability, administrators should reserve resources based on a target for resource use.

The node enforces resource constraints by using a new cgroup hierarchy that enforces quality of service. All pods are launched in a dedicated cgroup hierarchy that is separate from system daemons.

Administrators should treat system daemons similar to pods that have a guaranteed quality of service. System daemons can burst within their bounding control groups and this behavior must be managed as part of cluster deployments. Reserve CPU and memory resources for system daemons by specifying the amount of CPU and memory resources in system-reserved.

Enforcing system-reserved limits can prevent critical system services from receiving CPU and memory resources. As a result, a critical system service can be ended by the out-of-memory killer. The recommendation is to enforce system-reserved only if you have profiled the nodes exhaustively to determine precise estimates and you are confident that critical system services can recover if any process in that group is ended by the out-of-memory killer.

6.9.1.3. Understanding Eviction Thresholds

If a node is under memory pressure, it can impact the entire node and all pods running on the node. For example, a system daemon that uses more than its reserved amount of memory can trigger an out-of-memory event. To avoid or reduce the probability of system out-of-memory events, the node provides out-of-resource handling.

You can reserve some memory using the --eviction-hard flag. The node attempts to evict pods whenever memory availability on the node drops below the absolute value or percentage. If system daemons do not exist on a node, pods are limited to the memory capacity - eviction-hard. For this reason, resources set aside as a buffer for eviction before reaching out of memory conditions are not available for pods.

The following is an example to illustrate the impact of node allocatable for memory:

  • Node capacity is 32Gi
  • --system-reserved is 3Gi
  • --eviction-hard is set to 100Mi.

For this node, the effective node allocatable value is 28.9Gi. If the node and system components use all their reservation, the memory available for pods is 28.9Gi, and kubelet evicts pods when it exceeds this threshold.

If you enforce node allocatable, 28.9Gi, with top-level cgroups, then pods can never exceed 28.9Gi. Evictions are not performed unless system daemons consume more than 3.1Gi of memory.

If system daemons do not use up all their reservation, with the above example, pods would face memcg OOM kills from their bounding cgroup before node evictions kick in. To better enforce QoS under this situation, the node applies the hard eviction thresholds to the top-level cgroup for all pods to be Node Allocatable + Eviction Hard Thresholds.

If system daemons do not use up all their reservation, the node will evict pods whenever they consume more than 28.9Gi of memory. If eviction does not occur in time, a pod will be OOM killed if pods consume 29Gi of memory.

6.9.1.4. How the scheduler determines resource availability

The scheduler uses the value of node.Status.Allocatable instead of node.Status.Capacity to decide if a node will become a candidate for pod scheduling.

By default, the node will report its machine capacity as fully schedulable by the cluster.

6.9.2. Automatically allocating resources for nodes

OpenShift Container Platform can automatically determine the optimal system-reserved CPU and memory resources for nodes associated with a specific machine config pool and update the nodes with those values when the nodes start. By default, the system-reserved CPU is 500m and system-reserved memory is 1Gi.

To automatically determine and allocate the system-reserved resources on nodes, create a KubeletConfig custom resource (CR) to set the autoSizingReserved: true parameter. A script on each node calculates the optimal values for the respective reserved resources based on the installed CPU and memory capacity on each node. The script takes into account that increased capacity requires a corresponding increase in the reserved resources.

Automatically determining the optimal system-reserved settings ensures that your cluster is running efficiently and prevents node failure due to resource starvation of system components, such as CRI-O and kubelet, without your needing to manually calculate and update the values.

This feature is disabled by default.

Prerequisites

  1. Obtain the label associated with the static MachineConfigPool object for the type of node you want to configure by entering the following command:

    $ oc edit machineconfigpool <name>

    For example:

    $ oc edit machineconfigpool worker

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfigPool
    metadata:
      creationTimestamp: "2022-11-16T15:34:25Z"
      generation: 4
      labels:
        pools.operator.machineconfiguration.openshift.io/worker: "" 1
      name: worker
    #...

    1
    The label appears under Labels.
    Tip

    If an appropriate label is not present, add a key/value pair such as:

    $ oc label machineconfigpool worker custom-kubelet=small-pods

Procedure

  1. Create a custom resource (CR) for your configuration change:

    Sample configuration for a resource allocation CR

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: dynamic-node 1
    spec:
      autoSizingReserved: true 2
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 3
    #...

    1
    Assign a name to CR.
    2
    Add the autoSizingReserved parameter set to true to allow OpenShift Container Platform to automatically determine and allocate the system-reserved resources on the nodes associated with the specified label. To disable automatic allocation on those nodes, set this parameter to false.
    3
    Specify the label from the machine config pool that you configured in the "Prerequisites" section. You can choose any desired labels for the machine config pool, such as custom-kubelet: small-pods, or the default label, pools.operator.machineconfiguration.openshift.io/worker: "".

    The previous example enables automatic resource allocation on all worker nodes. OpenShift Container Platform drains the nodes, applies the kubelet config, and restarts the nodes.

  2. Create the CR by entering the following command:

    $ oc create -f <file_name>.yaml

Verification

  1. Log in to a node you configured by entering the following command:

    $ oc debug node/<node_name>
  2. Set /host as the root directory within the debug shell:

    # chroot /host
  3. View the /etc/node-sizing.env file:

    Example output

    SYSTEM_RESERVED_MEMORY=3Gi
    SYSTEM_RESERVED_CPU=0.08

    The kubelet uses the system-reserved values in the /etc/node-sizing.env file. In the previous example, the worker nodes are allocated 0.08 CPU and 3 Gi of memory. It can take several minutes for the optimal values to appear.

6.9.3. Manually allocating resources for nodes

OpenShift Container Platform supports the CPU and memory resource types for allocation. The ephemeral-resource resource type is also supported. For the cpu type, you specify the resource quantity in units of cores, such as 200m, 0.5, or 1. For memory and ephemeral-storage, you specify the resource quantity in units of bytes, such as 200Ki, 50Mi, or 5Gi. By default, the system-reserved CPU is 500m and system-reserved memory is 1Gi.

As an administrator, you can set these values by using a kubelet config custom resource (CR) through a set of <resource_type>=<resource_quantity> pairs (e.g., cpu=200m,memory=512Mi).

Important

You must use a kubelet config CR to manually set resource values. You cannot use a machine config CR.

For details on the recommended system-reserved values, refer to the recommended system-reserved values.

Prerequisites

  1. Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command:

    $ oc edit machineconfigpool <name>

    For example:

    $ oc edit machineconfigpool worker

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfigPool
    metadata:
      creationTimestamp: "2022-11-16T15:34:25Z"
      generation: 4
      labels:
        pools.operator.machineconfiguration.openshift.io/worker: "" 1
      name: worker
    #...

    1
    The label appears under Labels.
    Tip

    If the label is not present, add a key/value pair such as:

    $ oc label machineconfigpool worker custom-kubelet=small-pods

Procedure

  1. Create a custom resource (CR) for your configuration change.

    Sample configuration for a resource allocation CR

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: set-allocatable 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 2
      kubeletConfig:
        systemReserved: 3
          cpu: 1000m
          memory: 1Gi
    #...

    1
    Assign a name to CR.
    2
    Specify the label from the machine config pool.
    3
    Specify the resources to reserve for the node components and system components.
  2. Run the following command to create the CR:

    $ oc create -f <file_name>.yaml

6.10. Allocating specific CPUs for nodes in a cluster

When using the static CPU Manager policy, you can reserve specific CPUs for use by specific nodes in your cluster. For example, on a system with 24 CPUs, you could reserve CPUs numbered 0 - 3 for the control plane allowing the compute nodes to use CPUs 4 - 23.

6.10.1. Reserving CPUs for nodes

To explicitly define a list of CPUs that are reserved for specific nodes, create a KubeletConfig custom resource (CR) to define the reservedSystemCPUs parameter. This list supersedes the CPUs that might be reserved using the systemReserved parameter.

Procedure

  1. Obtain the label associated with the machine config pool (MCP) for the type of node you want to configure:

    $ oc describe machineconfigpool <name>

    For example:

    $ oc describe machineconfigpool worker

    Example output

    Name:         worker
    Namespace:
    Labels:       machineconfiguration.openshift.io/mco-built-in=
                  pools.operator.machineconfiguration.openshift.io/worker= 1
    Annotations:  <none>
    API Version:  machineconfiguration.openshift.io/v1
    Kind:         MachineConfigPool
    #...

    1
    Get the MCP label.
  2. Create a YAML file for the KubeletConfig CR:

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: set-reserved-cpus 1
    spec:
      kubeletConfig:
        reservedSystemCPUs: "0,1,2,3" 2
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 3
    #...
    1
    Specify a name for the CR.
    2
    Specify the core IDs of the CPUs you want to reserve for the nodes associated with the MCP.
    3
    Specify the label from the MCP.
  3. Create the CR object:

    $ oc create -f <file_name>.yaml

Additional resources

6.11. Enabling TLS security profiles for the kubelet

You can use a TLS (Transport Layer Security) security profile to define which TLS ciphers are required by the kubelet when it is acting as an HTTP server. The kubelet uses its HTTP/GRPC server to communicate with the Kubernetes API server, which sends commands to pods, gathers logs, and run exec commands on pods through the kubelet.

A TLS security profile defines the TLS ciphers that the Kubernetes API server must use when connecting with the kubelet to protect communication between the kubelet and the Kubernetes API server.

Note

By default, when the kubelet acts as a client with the Kubernetes API server, it automatically negotiates the TLS parameters with the API server.

6.11.1. Understanding TLS security profiles

You can use a TLS (Transport Layer Security) security profile to define which TLS ciphers are required by various OpenShift Container Platform components. The OpenShift Container Platform TLS security profiles are based on Mozilla recommended configurations.

You can specify one of the following TLS security profiles for each component:

Table 6.4. TLS security profiles
ProfileDescription

Old

This profile is intended for use with legacy clients or libraries. The profile is based on the Old backward compatibility recommended configuration.

The Old profile requires a minimum TLS version of 1.0.

Note

For the Ingress Controller, the minimum TLS version is converted from 1.0 to 1.1.

Intermediate

This profile is the recommended configuration for the majority of clients. It is the default TLS security profile for the Ingress Controller, kubelet, and control plane. The profile is based on the Intermediate compatibility recommended configuration.

The Intermediate profile requires a minimum TLS version of 1.2.

Modern

This profile is intended for use with modern clients that have no need for backwards compatibility. This profile is based on the Modern compatibility recommended configuration.

The Modern profile requires a minimum TLS version of 1.3.

Custom

This profile allows you to define the TLS version and ciphers to use.

Warning

Use caution when using a Custom profile, because invalid configurations can cause problems.

Note

When using one of the predefined profile types, the effective profile configuration is subject to change between releases. For example, given a specification to use the Intermediate profile deployed on release X.Y.Z, an upgrade to release X.Y.Z+1 might cause a new profile configuration to be applied, resulting in a rollout.

6.11.2. Configuring the TLS security profile for the kubelet

To configure a TLS security profile for the kubelet when it is acting as an HTTP server, create a KubeletConfig custom resource (CR) to specify a predefined or custom TLS security profile for specific nodes. If a TLS security profile is not configured, the default TLS security profile is Intermediate.

Sample KubeletConfig CR that configures the Old TLS security profile on worker nodes

apiVersion: config.openshift.io/v1
kind: KubeletConfig
 ...
spec:
  tlsSecurityProfile:
    old: {}
    type: Old
  machineConfigPoolSelector:
    matchLabels:
      pools.operator.machineconfiguration.openshift.io/worker: ""
#...

You can see the ciphers and the minimum TLS version of the configured TLS security profile in the kubelet.conf file on a configured node.

Prerequisites

  • You have access to the cluster as a user with the cluster-admin role.

Procedure

  1. Create a KubeletConfig CR to configure the TLS security profile:

    Sample KubeletConfig CR for a Custom profile

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: set-kubelet-tls-security-profile
    spec:
      tlsSecurityProfile:
        type: Custom 1
        custom: 2
          ciphers: 3
          - ECDHE-ECDSA-CHACHA20-POLY1305
          - ECDHE-RSA-CHACHA20-POLY1305
          - ECDHE-RSA-AES128-GCM-SHA256
          - ECDHE-ECDSA-AES128-GCM-SHA256
          minTLSVersion: VersionTLS11
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 4
    #...

    1
    Specify the TLS security profile type (Old, Intermediate, or Custom). The default is Intermediate.
    2
    Specify the appropriate field for the selected type:
    • old: {}
    • intermediate: {}
    • custom:
    3
    For the custom type, specify a list of TLS ciphers and minimum accepted TLS version.
    4
    Optional: Specify the machine config pool label for the nodes you want to apply the TLS security profile.
  2. Create the KubeletConfig object:

    $ oc create -f <filename>

    Depending on the number of worker nodes in the cluster, wait for the configured nodes to be rebooted one by one.

Verification

To verify that the profile is set, perform the following steps after the nodes are in the Ready state:

  1. Start a debug session for a configured node:

    $ oc debug node/<node_name>
  2. Set /host as the root directory within the debug shell:

    sh-4.4# chroot /host
  3. View the kubelet.conf file:

    sh-4.4# cat /etc/kubernetes/kubelet.conf

    Example output

      "kind": "KubeletConfiguration",
      "apiVersion": "kubelet.config.k8s.io/v1beta1",
    #...
      "tlsCipherSuites": [
        "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256",
        "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256",
        "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384",
        "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384",
        "TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256",
        "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256"
      ],
      "tlsMinVersion": "VersionTLS12",
    #...

6.12. Machine Config Daemon metrics

The Machine Config Daemon is a part of the Machine Config Operator. It runs on every node in the cluster. The Machine Config Daemon manages configuration changes and updates on each of the nodes.

6.12.1. Machine Config Daemon metrics

Beginning with OpenShift Container Platform 4.3, the Machine Config Daemon provides a set of metrics. These metrics can be accessed using the Prometheus Cluster Monitoring stack.

The following table describes this set of metrics. Some entries contain commands for getting specific logs. However, the most comprehensive set of logs is available using the oc adm must-gather command.

Note

Metrics marked with * in the Name and Description columns represent serious errors that might cause performance problems. Such problems might prevent updates and upgrades from proceeding.

Table 6.5. MCO metrics
NameFormatDescriptionNotes

mcd_host_os_and_version

[]string{"os", "version"}

Shows the OS that MCD is running on, such as RHCOS or RHEL. In case of RHCOS, the version is provided.

 

mcd_drain_err*

 

Logs errors received during failed drain. *

While drains might need multiple tries to succeed, terminal failed drains prevent updates from proceeding. The drain_time metric, which shows how much time the drain took, might help with troubleshooting.

For further investigation, see the logs by running:

$ oc logs -f -n openshift-machine-config-operator machine-config-daemon-<hash> -c machine-config-daemon

mcd_pivot_err*

[]string{"err", "node", "pivot_target"}

Logs errors encountered during pivot. *

Pivot errors might prevent OS upgrades from proceeding.

For further investigation, run this command to see the logs from the machine-config-daemon container:

$ oc logs -f -n openshift-machine-config-operator machine-config-daemon-<hash> -c machine-config-daemon

mcd_state

[]string{"state", "reason"}

State of Machine Config Daemon for the indicated node. Possible states are "Done", "Working", and "Degraded". In case of "Degraded", the reason is included.

For further investigation, see the logs by running:

$ oc logs -f -n openshift-machine-config-operator machine-config-daemon-<hash> -c machine-config-daemon

mcd_kubelet_state*

 

Logs kubelet health failures. *

This is expected to be empty, with failure count of 0. If failure count exceeds 2, the error indicating threshold is exceeded. This indicates a possible issue with the health of the kubelet.

For further investigation, run this command to access the node and see all its logs:

$ oc debug node/<node> — chroot /host journalctl -u kubelet

mcd_reboot_err*

[]string{"message", "err", "node"}

Logs the failed reboots and the corresponding errors. *

This is expected to be empty, which indicates a successful reboot.

For further investigation, see the logs by running:

$ oc logs -f -n openshift-machine-config-operator machine-config-daemon-<hash> -c machine-config-daemon

mcd_update_state

[]string{"config", "err"}

Logs success or failure of configuration updates and the corresponding errors.

The expected value is rendered-master/rendered-worker-XXXX. If the update fails, an error is present.

For further investigation, see the logs by running:

$ oc logs -f -n openshift-machine-config-operator machine-config-daemon-<hash> -c machine-config-daemon

6.13. Creating infrastructure nodes

Important

You can use the advanced machine management and scaling capabilities only in clusters where the Machine API is operational. Clusters with user-provisioned infrastructure require additional validation and configuration to use the Machine API.

Clusters with the infrastructure platform type none cannot use the Machine API. This limitation applies even if the compute machines that are attached to the cluster are installed on a platform that supports the feature. This parameter cannot be changed after installation.

To view the platform type for your cluster, run the following command:

$ oc get infrastructure cluster -o jsonpath='{.status.platform}'

You can use infrastructure machine sets to create machines that host only infrastructure components, such as the default router, the integrated container image registry, and the components for cluster metrics and monitoring. These infrastructure machines are not counted toward the total number of subscriptions that are required to run the environment.

In a production deployment, it is recommended that you deploy at least three machine sets to hold infrastructure components. Both OpenShift Logging and Red Hat OpenShift Service Mesh deploy Elasticsearch, which requires three instances to be installed on different nodes. Each of these nodes can be deployed to different availability zones for high availability. This configuration requires three different machine sets, one for each availability zone. In global Azure regions that do not have multiple availability zones, you can use availability sets to ensure high availability.

Note

After adding the NoSchedule taint on the infrastructure node, existing DNS pods running on that node are marked as misscheduled. You must either delete or add toleration on misscheduled DNS pods.

6.13.1. OpenShift Container Platform infrastructure components

Each self-managed Red Hat OpenShift subscription includes entitlements for OpenShift Container Platform and other OpenShift-related components. These entitlements are included for running OpenShift Container Platform control plane and infrastructure workloads and do not need to be accounted for during sizing.

To qualify as an infrastructure node and use the included entitlement, only components that are supporting the cluster, and not part of an end-user application, can run on those instances. Examples include the following components:

  • Kubernetes and OpenShift Container Platform control plane services
  • The default router
  • The integrated container image registry
  • The HAProxy-based Ingress Controller
  • The cluster metrics collection, or monitoring service, including components for monitoring user-defined projects
  • Cluster aggregated logging
  • Red Hat Quay
  • Red Hat OpenShift Data Foundation
  • Red Hat Advanced Cluster Management for Kubernetes
  • Red Hat Advanced Cluster Security for Kubernetes
  • Red Hat OpenShift GitOps
  • Red Hat OpenShift Pipelines
  • Red Hat OpenShift Service Mesh

Any node that runs any other container, pod, or component is a worker node that your subscription must cover.

For information about infrastructure nodes and which components can run on infrastructure nodes, see the "Red Hat OpenShift control plane and infrastructure nodes" section in the OpenShift sizing and subscription guide for enterprise Kubernetes document.

To create an infrastructure node, you can use a machine set, label the node, or use a machine config pool.

6.13.1.1. Creating an infrastructure node
Important

See Creating infrastructure machine sets for installer-provisioned infrastructure environments or for any cluster where the control plane nodes are managed by the machine API.

Requirements of the cluster dictate that infrastructure, also called infra nodes, be provisioned. The installer only provides provisions for control plane and worker nodes. Worker nodes can be designated as infrastructure nodes or application, also called app, nodes through labeling.

Procedure

  1. Add a label to the worker node that you want to act as application node:

    $ oc label node <node-name> node-role.kubernetes.io/app=""
  2. Add a label to the worker nodes that you want to act as infrastructure nodes:

    $ oc label node <node-name> node-role.kubernetes.io/infra=""
  3. Check to see if applicable nodes now have the infra role and app roles:

    $ oc get nodes
  4. Create a default cluster-wide node selector. The default node selector is applied to pods created in all namespaces. This creates an intersection with any existing node selectors on a pod, which additionally constrains the pod’s selector.

    Important

    If the default node selector key conflicts with the key of a pod’s label, then the default node selector is not applied.

    However, do not set a default node selector that might cause a pod to become unschedulable. For example, setting the default node selector to a specific node role, such as node-role.kubernetes.io/infra="", when a pod’s label is set to a different node role, such as node-role.kubernetes.io/master="", can cause the pod to become unschedulable. For this reason, use caution when setting the default node selector to specific node roles.

    You can alternatively use a project node selector to avoid cluster-wide node selector key conflicts.

    1. Edit the Scheduler object:

      $ oc edit scheduler cluster
    2. Add the defaultNodeSelector field with the appropriate node selector:

      apiVersion: config.openshift.io/v1
      kind: Scheduler
      metadata:
        name: cluster
      spec:
        defaultNodeSelector: node-role.kubernetes.io/infra="" 1
      # ...
      1
      This example node selector deploys pods on infrastructure nodes by default.
    3. Save the file to apply the changes.

You can now move infrastructure resources to the newly labeled infra nodes.

Chapter 7. Working with containers

7.1. Understanding Containers

The basic units of OpenShift Container Platform applications are called containers. Linux container technologies are lightweight mechanisms for isolating running processes so that they are limited to interacting with only their designated resources.

Many application instances can be running in containers on a single host without visibility into each others' processes, files, network, and so on. Typically, each container provides a single service (often called a "micro-service"), such as a web server or a database, though containers can be used for arbitrary workloads.

The Linux kernel has been incorporating capabilities for container technologies for years. OpenShift Container Platform and Kubernetes add the ability to orchestrate containers across multi-host installations.

7.1.1. About containers and RHEL kernel memory

Due to Red Hat Enterprise Linux (RHEL) behavior, a container on a node with high CPU usage might seem to consume more memory than expected. The higher memory consumption could be caused by the kmem_cache in the RHEL kernel. The RHEL kernel creates a kmem_cache for each cgroup. For added performance, the kmem_cache contains a cpu_cache, and a node cache for any NUMA nodes. These caches all consume kernel memory.

The amount of memory stored in those caches is proportional to the number of CPUs that the system uses. As a result, a higher number of CPUs results in a greater amount of kernel memory being held in these caches. Higher amounts of kernel memory in these caches can cause OpenShift Container Platform containers to exceed the configured memory limits, resulting in the container being killed.

To avoid losing containers due to kernel memory issues, ensure that the containers request sufficient memory. You can use the following formula to estimate the amount of memory consumed by the kmem_cache, where nproc is the number of processing units available that are reported by the nproc command. The lower limit of container requests should be this value plus the container memory requirements:

$(nproc) X 1/2 MiB

7.1.2. About the container engine and container runtime

A container engine is a piece of software that processes user requests, including command line options and image pulls. The container engine uses a container runtime, also called a lower-level container runtime, to run and manage the components required to deploy and operate containers. You likely will not need to interact with the container engine or container runtime.

Note

The OpenShift Container Platform documentation uses the term container runtime to refer to the lower-level container runtime. Other documentation can refer to the container engine as the container runtime.

OpenShift Container Platform uses CRI-O as the container engine and runC or crun as the container runtime. The default container runtime is runC. Both container runtimes adhere to the Open Container Initiative (OCI) runtime specifications.

CRI-O is a Kubernetes-native container engine implementation that integrates closely with the operating system to deliver an efficient and optimized Kubernetes experience. The CRI-O container engine runs as a systemd service on each OpenShift Container Platform cluster node.

runC, developed by Docker and maintained by the Open Container Project, is a lightweight, portable container runtime written in Go. crun, developed by Red Hat, is a fast and low-memory container runtime fully written in C. As of OpenShift Container Platform 4.12, you can select between the two.

Important

crun container runtime support is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

crun has several improvements over runC, including:

  • Smaller binary
  • Quicker processing
  • Lower memory footprint

runC has some benefits over crun, including:

  • Most popular OCI container runtime.
  • Longer tenure in production.
  • Default container runtime of CRI-O.

You can move between the two container runtimes as needed.

For information on setting which container runtime to use, see Creating a ContainerRuntimeConfig CR to edit CRI-O parameters.

7.2. Using Init Containers to perform tasks before a pod is deployed

OpenShift Container Platform provides init containers, which are specialized containers that run before application containers and can contain utilities or setup scripts not present in an app image.

7.2.1. Understanding Init Containers

You can use an Init Container resource to perform tasks before the rest of a pod is deployed.

A pod can have Init Containers in addition to application containers. Init containers allow you to reorganize setup scripts and binding code.

An Init Container can:

  • Contain and run utilities that are not desirable to include in the app Container image for security reasons.
  • Contain utilities or custom code for setup that is not present in an app image. For example, there is no requirement to make an image FROM another image just to use a tool like sed, awk, python, or dig during setup.
  • Use Linux namespaces so that they have different filesystem views from app containers, such as access to secrets that application containers are not able to access.

Each Init Container must complete successfully before the next one is started. So, Init Containers provide an easy way to block or delay the startup of app containers until some set of preconditions are met.

For example, the following are some ways you can use Init Containers:

  • Wait for a service to be created with a shell command like:

    for i in {1..100}; do sleep 1; if dig myservice; then exit 0; fi; done; exit 1
  • Register this pod with a remote server from the downward API with a command like:

    $ curl -X POST http://$MANAGEMENT_SERVICE_HOST:$MANAGEMENT_SERVICE_PORT/register -d ‘instance=$()&ip=$()’
  • Wait for some time before starting the app Container with a command like sleep 60.
  • Clone a git repository into a volume.
  • Place values into a configuration file and run a template tool to dynamically generate a configuration file for the main app Container. For example, place the POD_IP value in a configuration and generate the main app configuration file using Jinja.

See the Kubernetes documentation for more information.

7.2.2. Creating Init Containers

The following example outlines a simple pod which has two Init Containers. The first waits for myservice and the second waits for mydb. After both containers complete, the pod begins.

Procedure

  1. Create the pod for the Init Container:

    1. Create a YAML file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: myapp-pod
        labels:
          app: myapp
      spec:
        containers:
        - name: myapp-container
          image: registry.access.redhat.com/ubi8/ubi:latest
          command: ['sh', '-c', 'echo The app is running! && sleep 3600']
        initContainers:
        - name: init-myservice
          image: registry.access.redhat.com/ubi8/ubi:latest
          command: ['sh', '-c', 'until getent hosts myservice; do echo waiting for myservice; sleep 2; done;']
        - name: init-mydb
          image: registry.access.redhat.com/ubi8/ubi:latest
          command: ['sh', '-c', 'until getent hosts mydb; do echo waiting for mydb; sleep 2; done;']
      # ...
    2. Create the pod:

      $ oc create -f myapp.yaml
    3. View the status of the pod:

      $ oc get pods

      Example output

      NAME                          READY     STATUS              RESTARTS   AGE
      myapp-pod                     0/1       Init:0/2            0          5s

      The pod status, Init:0/2, indicates it is waiting for the two services.

  2. Create the myservice service.

    1. Create a YAML file similar to the following:

      kind: Service
      apiVersion: v1
      metadata:
        name: myservice
      spec:
        ports:
        - protocol: TCP
          port: 80
          targetPort: 9376
    2. Create the pod:

      $ oc create -f myservice.yaml
    3. View the status of the pod:

      $ oc get pods

      Example output

      NAME                          READY     STATUS              RESTARTS   AGE
      myapp-pod                     0/1       Init:1/2            0          5s

      The pod status, Init:1/2, indicates it is waiting for one service, in this case the mydb service.

  3. Create the mydb service:

    1. Create a YAML file similar to the following:

      kind: Service
      apiVersion: v1
      metadata:
        name: mydb
      spec:
        ports:
        - protocol: TCP
          port: 80
          targetPort: 9377
    2. Create the pod:

      $ oc create -f mydb.yaml
    3. View the status of the pod:

      $ oc get pods

      Example output

      NAME                          READY     STATUS              RESTARTS   AGE
      myapp-pod                     1/1       Running             0          2m

      The pod status indicated that it is no longer waiting for the services and is running.

7.3. Using volumes to persist container data

Files in a container are ephemeral. As such, when a container crashes or stops, the data is lost. You can use volumes to persist the data used by the containers in a pod. A volume is directory, accessible to the Containers in a pod, where data is stored for the life of the pod.

7.3.1. Understanding volumes

Volumes are mounted file systems available to pods and their containers which may be backed by a number of host-local or network attached storage endpoints. Containers are not persistent by default; on restart, their contents are cleared.

To ensure that the file system on the volume contains no errors and, if errors are present, to repair them when possible, OpenShift Container Platform invokes the fsck utility prior to the mount utility. This occurs when either adding a volume or updating an existing volume.

The simplest volume type is emptyDir, which is a temporary directory on a single machine. Administrators may also allow you to request a persistent volume that is automatically attached to your pods.

Note

emptyDir volume storage may be restricted by a quota based on the pod’s FSGroup, if the FSGroup parameter is enabled by your cluster administrator.

7.3.2. Working with volumes using the OpenShift Container Platform CLI

You can use the CLI command oc set volume to add and remove volumes and volume mounts for any object that has a pod template like replication controllers or deployment configs. You can also list volumes in pods or any object that has a pod template.

The oc set volume command uses the following general syntax:

$ oc set volume <object_selection> <operation> <mandatory_parameters> <options>
Object selection
Specify one of the following for the object_selection parameter in the oc set volume command:
Table 7.1. Object Selection
SyntaxDescriptionExample

<object_type> <name>

Selects <name> of type <object_type>.

deploymentConfig registry

<object_type>/<name>

Selects <name> of type <object_type>.

deploymentConfig/registry

<object_type>--selector=<object_label_selector>

Selects resources of type <object_type> that matched the given label selector.

deploymentConfig--selector="name=registry"

<object_type> --all

Selects all resources of type <object_type>.

deploymentConfig --all

-f or --filename=<file_name>

File name, directory, or URL to file to use to edit the resource.

-f registry-deployment-config.json

Operation
Specify --add or --remove for the operation parameter in the oc set volume command.
Mandatory parameters
Any mandatory parameters are specific to the selected operation and are discussed in later sections.
Options
Any options are specific to the selected operation and are discussed in later sections.

7.3.3. Listing volumes and volume mounts in a pod

You can list volumes and volume mounts in pods or pod templates:

Procedure

To list volumes:

$ oc set volume <object_type>/<name> [options]

List volume supported options:

OptionDescriptionDefault

--name

Name of the volume.

 

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

For example:

  • To list all volumes for pod p1:

    $ oc set volume pod/p1
  • To list volume v1 defined on all deployment configs:

    $ oc set volume dc --all --name=v1

7.3.4. Adding volumes to a pod

You can add volumes and volume mounts to a pod.

Procedure

To add a volume, a volume mount, or both to pod templates:

$ oc set volume <object_type>/<name> --add [options]
Table 7.2. Supported Options for Adding Volumes
OptionDescriptionDefault

--name

Name of the volume.

Automatically generated, if not specified.

-t, --type

Name of the volume source. Supported values: emptyDir, hostPath, secret, configmap, persistentVolumeClaim or projected.

emptyDir

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

-m, --mount-path

Mount path inside the selected containers. Do not mount to the container root, /, or any path that is the same in the host and the container. This can corrupt your host system if the container is sufficiently privileged, such as the host /dev/pts files. It is safe to mount the host by using /host.

 

--path

Host path. Mandatory parameter for --type=hostPath. Do not mount to the container root, /, or any path that is the same in the host and the container. This can corrupt your host system if the container is sufficiently privileged, such as the host /dev/pts files. It is safe to mount the host by using /host.

 

--secret-name

Name of the secret. Mandatory parameter for --type=secret.

 

--configmap-name

Name of the configmap. Mandatory parameter for --type=configmap.

 

--claim-name

Name of the persistent volume claim. Mandatory parameter for --type=persistentVolumeClaim.

 

--source

Details of volume source as a JSON string. Recommended if the desired volume source is not supported by --type.

 

-o, --output

Display the modified objects instead of updating them on the server. Supported values: json, yaml.

 

--output-version

Output the modified objects with the given version.

api-version

For example:

  • To add a new volume source emptyDir to the registry DeploymentConfig object:

    $ oc set volume dc/registry --add
    Tip

    You can alternatively apply the following YAML to add the volume:

    Example 7.1. Sample deployment config with an added volume

    kind: DeploymentConfig
    apiVersion: apps.openshift.io/v1
    metadata:
      name: registry
      namespace: registry
    spec:
      replicas: 3
      selector:
        app: httpd
      template:
        metadata:
          labels:
            app: httpd
        spec:
          volumes: 1
            - name: volume-pppsw
              emptyDir: {}
          containers:
            - name: httpd
              image: >-
                image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
              ports:
                - containerPort: 8080
                  protocol: TCP
    1
    Add the volume source emptyDir.
  • To add volume v1 with secret secret1 for replication controller r1 and mount inside the containers at /data:

    $ oc set volume rc/r1 --add --name=v1 --type=secret --secret-name='secret1' --mount-path=/data
    Tip

    You can alternatively apply the following YAML to add the volume:

    Example 7.2. Sample replication controller with added volume and secret

    kind: ReplicationController
    apiVersion: v1
    metadata:
      name: example-1
      namespace: example
    spec:
      replicas: 0
      selector:
        app: httpd
        deployment: example-1
        deploymentconfig: example
      template:
        metadata:
          creationTimestamp: null
          labels:
            app: httpd
            deployment: example-1
            deploymentconfig: example
        spec:
          volumes: 1
            - name: v1
              secret:
                secretName: secret1
                defaultMode: 420
          containers:
            - name: httpd
              image: >-
                image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
              volumeMounts: 2
                - name: v1
                  mountPath: /data
    1
    Add the volume and secret.
    2
    Add the container mount path.
  • To add existing persistent volume v1 with claim name pvc1 to deployment configuration dc.json on disk, mount the volume on container c1 at /data, and update the DeploymentConfig object on the server:

    $ oc set volume -f dc.json --add --name=v1 --type=persistentVolumeClaim \
      --claim-name=pvc1 --mount-path=/data --containers=c1
    Tip

    You can alternatively apply the following YAML to add the volume:

    Example 7.3. Sample deployment config with persistent volume added

    kind: DeploymentConfig
    apiVersion: apps.openshift.io/v1
    metadata:
      name: example
      namespace: example
    spec:
      replicas: 3
      selector:
        app: httpd
      template:
        metadata:
          labels:
            app: httpd
        spec:
          volumes:
            - name: volume-pppsw
              emptyDir: {}
            - name: v1 1
              persistentVolumeClaim:
                claimName: pvc1
          containers:
            - name: httpd
              image: >-
                image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
              ports:
                - containerPort: 8080
                  protocol: TCP
              volumeMounts: 2
                - name: v1
                  mountPath: /data
    1
    Add the persistent volume claim named `pvc1.
    2
    Add the container mount path.
  • To add a volume v1 based on Git repository https://github.com/namespace1/project1 with revision 5125c45f9f563 for all replication controllers:

    $ oc set volume rc --all --add --name=v1 \
      --source='{"gitRepo": {
                    "repository": "https://github.com/namespace1/project1",
                    "revision": "5125c45f9f563"
                }}'

7.3.5. Updating volumes and volume mounts in a pod

You can modify the volumes and volume mounts in a pod.

Procedure

Updating existing volumes using the --overwrite option:

$ oc set volume <object_type>/<name> --add --overwrite [options]

For example:

  • To replace existing volume v1 for replication controller r1 with existing persistent volume claim pvc1:

    $ oc set volume rc/r1 --add --overwrite --name=v1 --type=persistentVolumeClaim --claim-name=pvc1
    Tip

    You can alternatively apply the following YAML to replace the volume:

    Example 7.4. Sample replication controller with persistent volume claim named pvc1

    kind: ReplicationController
    apiVersion: v1
    metadata:
      name: example-1
      namespace: example
    spec:
      replicas: 0
      selector:
        app: httpd
        deployment: example-1
        deploymentconfig: example
      template:
        metadata:
          labels:
            app: httpd
            deployment: example-1
            deploymentconfig: example
        spec:
          volumes:
            - name: v1 1
              persistentVolumeClaim:
                claimName: pvc1
          containers:
            - name: httpd
              image: >-
                image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
              ports:
                - containerPort: 8080
                  protocol: TCP
              volumeMounts:
                - name: v1
                  mountPath: /data
    1
    Set persistent volume claim to pvc1.
  • To change the DeploymentConfig object d1 mount point to /opt for volume v1:

    $ oc set volume dc/d1 --add --overwrite --name=v1 --mount-path=/opt
    Tip

    You can alternatively apply the following YAML to change the mount point:

    Example 7.5. Sample deployment config with mount point set to opt.

    kind: DeploymentConfig
    apiVersion: apps.openshift.io/v1
    metadata:
      name: example
      namespace: example
    spec:
      replicas: 3
      selector:
        app: httpd
      template:
        metadata:
          labels:
            app: httpd
        spec:
          volumes:
            - name: volume-pppsw
              emptyDir: {}
            - name: v2
              persistentVolumeClaim:
                claimName: pvc1
            - name: v1
              persistentVolumeClaim:
                claimName: pvc1
          containers:
            - name: httpd
              image: >-
                image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest
              ports:
                - containerPort: 8080
                  protocol: TCP
              volumeMounts: 1
                - name: v1
                  mountPath: /opt
    1
    Set the mount point to /opt.

7.3.6. Removing volumes and volume mounts from a pod

You can remove a volume or volume mount from a pod.

Procedure

To remove a volume from pod templates:

$ oc set volume <object_type>/<name> --remove [options]
Table 7.3. Supported options for removing volumes
OptionDescriptionDefault

--name

Name of the volume.

 

-c, --containers

Select containers by name. It can also take wildcard '*' that matches any character.

'*'

--confirm

Indicate that you want to remove multiple volumes at once.

 

-o, --output

Display the modified objects instead of updating them on the server. Supported values: json, yaml.

 

--output-version

Output the modified objects with the given version.

api-version

For example:

  • To remove a volume v1 from the DeploymentConfig object d1:

    $ oc set volume dc/d1 --remove --name=v1
  • To unmount volume v1 from container c1 for the DeploymentConfig object d1 and remove the volume v1 if it is not referenced by any containers on d1:

    $ oc set volume dc/d1 --remove --name=v1 --containers=c1
  • To remove all volumes for replication controller r1:

    $ oc set volume rc/r1 --remove --confirm

7.3.7. Configuring volumes for multiple uses in a pod

You can configure a volume to allows you to share one volume for multiple uses in a single pod using the volumeMounts.subPath property to specify a subPath value inside a volume instead of the volume’s root.

Note

You cannot add a subPath parameter to an existing scheduled pod.

Procedure

  1. To view the list of files in the volume, run the oc rsh command:

    $ oc rsh <pod>

    Example output

    sh-4.2$ ls /path/to/volume/subpath/mount
    example_file1 example_file2 example_file3

  2. Specify the subPath:

    Example Pod spec with subPath parameter

    apiVersion: v1
    kind: Pod
    metadata:
      name: my-site
    spec:
        containers:
        - name: mysql
          image: mysql
          volumeMounts:
          - mountPath: /var/lib/mysql
            name: site-data
            subPath: mysql 1
        - name: php
          image: php
          volumeMounts:
          - mountPath: /var/www/html
            name: site-data
            subPath: html 2
        volumes:
        - name: site-data
          persistentVolumeClaim:
            claimName: my-site-data

    1
    Databases are stored in the mysql folder.
    2
    HTML content is stored in the html folder.

7.4. Mapping volumes using projected volumes

A projected volume maps several existing volume sources into the same directory.

The following types of volume sources can be projected:

  • Secrets
  • Config Maps
  • Downward API
Note

All sources are required to be in the same namespace as the pod.

7.4.1. Understanding projected volumes

Projected volumes can map any combination of these volume sources into a single directory, allowing the user to:

  • automatically populate a single volume with the keys from multiple secrets, config maps, and with downward API information, so that I can synthesize a single directory with various sources of information;
  • populate a single volume with the keys from multiple secrets, config maps, and with downward API information, explicitly specifying paths for each item, so that I can have full control over the contents of that volume.
Important

When the RunAsUser permission is set in the security context of a Linux-based pod, the projected files have the correct permissions set, including container user ownership. However, when the Windows equivalent RunAsUsername permission is set in a Windows pod, the kubelet is unable to correctly set ownership on the files in the projected volume.

Therefore, the RunAsUsername permission set in the security context of a Windows pod is not honored for Windows projected volumes running in OpenShift Container Platform.

The following general scenarios show how you can use projected volumes.

Config map, secrets, Downward API.
Projected volumes allow you to deploy containers with configuration data that includes passwords. An application using these resources could be deploying Red Hat OpenStack Platform (RHOSP) on Kubernetes. The configuration data might have to be assembled differently depending on if the services are going to be used for production or for testing. If a pod is labeled with production or testing, the downward API selector metadata.labels can be used to produce the correct RHOSP configs.
Config map + secrets.
Projected volumes allow you to deploy containers involving configuration data and passwords. For example, you might execute a config map with some sensitive encrypted tasks that are decrypted using a vault password file.
ConfigMap + Downward API.
Projected volumes allow you to generate a config including the pod name (available via the metadata.name selector). This application can then pass the pod name along with requests to easily determine the source without using IP tracking.
Secrets + Downward API.
Projected volumes allow you to use a secret as a public key to encrypt the namespace of the pod (available via the metadata.namespace selector). This example allows the Operator to use the application to deliver the namespace information securely without using an encrypted transport.
7.4.1.1. Example Pod specs

The following are examples of Pod specs for creating projected volumes.

Pod with a secret, a Downward API, and a config map

apiVersion: v1
kind: Pod
metadata:
  name: volume-test
spec:
  containers:
  - name: container-test
    image: busybox
    volumeMounts: 1
    - name: all-in-one
      mountPath: "/projected-volume"2
      readOnly: true 3
  volumes: 4
  - name: all-in-one 5
    projected:
      defaultMode: 0400 6
      sources:
      - secret:
          name: mysecret 7
          items:
            - key: username
              path: my-group/my-username 8
      - downwardAPI: 9
          items:
            - path: "labels"
              fieldRef:
                fieldPath: metadata.labels
            - path: "cpu_limit"
              resourceFieldRef:
                containerName: container-test
                resource: limits.cpu
      - configMap: 10
          name: myconfigmap
          items:
            - key: config
              path: my-group/my-config
              mode: 0777 11

1
Add a volumeMounts section for each container that needs the secret.
2
Specify a path to an unused directory where the secret will appear.
3
Set readOnly to true.
4
Add a volumes block to list each projected volume source.
5
Specify any name for the volume.
6
Set the execute permission on the files.
7
Add a secret. Enter the name of the secret object. Each secret you want to use must be listed.
8
Specify the path to the secrets file under the mountPath. Here, the secrets file is in /projected-volume/my-group/my-username.
9
Add a Downward API source.
10
Add a ConfigMap source.
11
Set the mode for the specific projection
Note

If there are multiple containers in the pod, each container needs a volumeMounts section, but only one volumes section is needed.

Pod with multiple secrets with a non-default permission mode set

apiVersion: v1
kind: Pod
metadata:
  name: volume-test
spec:
  containers:
  - name: container-test
    image: busybox
    volumeMounts:
    - name: all-in-one
      mountPath: "/projected-volume"
      readOnly: true
  volumes:
  - name: all-in-one
    projected:
      defaultMode: 0755
      sources:
      - secret:
          name: mysecret
          items:
            - key: username
              path: my-group/my-username
      - secret:
          name: mysecret2
          items:
            - key: password
              path: my-group/my-password
              mode: 511

Note

The defaultMode can only be specified at the projected level and not for each volume source. However, as illustrated above, you can explicitly set the mode for each individual projection.

7.4.1.2. Pathing Considerations
Collisions Between Keys when Configured Paths are Identical

If you configure any keys with the same path, the pod spec will not be accepted as valid. In the following example, the specified path for mysecret and myconfigmap are the same:

apiVersion: v1
kind: Pod
metadata:
  name: volume-test
spec:
  containers:
  - name: container-test
    image: busybox
    volumeMounts:
    - name: all-in-one
      mountPath: "/projected-volume"
      readOnly: true
  volumes:
  - name: all-in-one
    projected:
      sources:
      - secret:
          name: mysecret
          items:
            - key: username
              path: my-group/data
      - configMap:
          name: myconfigmap
          items:
            - key: config
              path: my-group/data

Consider the following situations related to the volume file paths.

Collisions Between Keys without Configured Paths
The only run-time validation that can occur is when all the paths are known at pod creation, similar to the above scenario. Otherwise, when a conflict occurs the most recent specified resource will overwrite anything preceding it (this is true for resources that are updated after pod creation as well).
Collisions when One Path is Explicit and the Other is Automatically Projected
In the event that there is a collision due to a user specified path matching data that is automatically projected, the latter resource will overwrite anything preceding it as before

7.4.2. Configuring a Projected Volume for a Pod

When creating projected volumes, consider the volume file path situations described in Understanding projected volumes.

The following example shows how to use a projected volume to mount an existing secret volume source. The steps can be used to create a user name and password secrets from local files. You then create a pod that runs one container, using a projected volume to mount the secrets into the same shared directory.

The user name and password values can be any valid string that is base64 encoded.

The following example shows admin in base64:

$ echo -n "admin" | base64

Example output

YWRtaW4=

The following example shows the password 1f2d1e2e67df in base64:

$ echo -n "1f2d1e2e67df" | base64

Example output

MWYyZDFlMmU2N2Rm

Procedure

To use a projected volume to mount an existing secret volume source.

  1. Create the secret:

    1. Create a YAML file similar to the following, replacing the password and user information as appropriate:

      apiVersion: v1
      kind: Secret
      metadata:
        name: mysecret
      type: Opaque
      data:
        pass: MWYyZDFlMmU2N2Rm
        user: YWRtaW4=
    2. Use the following command to create the secret:

      $ oc create -f <secrets-filename>

      For example:

      $ oc create -f secret.yaml

      Example output

      secret "mysecret" created

    3. You can check that the secret was created using the following commands:

      $ oc get secret <secret-name>

      For example:

      $ oc get secret mysecret

      Example output

      NAME       TYPE      DATA      AGE
      mysecret   Opaque    2         17h

      $ oc get secret <secret-name> -o yaml

      For example:

      $ oc get secret mysecret -o yaml
      apiVersion: v1
      data:
        pass: MWYyZDFlMmU2N2Rm
        user: YWRtaW4=
      kind: Secret
      metadata:
        creationTimestamp: 2017-05-30T20:21:38Z
        name: mysecret
        namespace: default
        resourceVersion: "2107"
        selfLink: /api/v1/namespaces/default/secrets/mysecret
        uid: 959e0424-4575-11e7-9f97-fa163e4bd54c
      type: Opaque
  2. Create a pod with a projected volume.

    1. Create a YAML file similar to the following, including a volumes section:

      kind: Pod
      metadata:
        name: test-projected-volume
      spec:
        containers:
        - name: test-projected-volume
          image: busybox
          args:
          - sleep
          - "86400"
          volumeMounts:
          - name: all-in-one
            mountPath: "/projected-volume"
            readOnly: true
            securityContext:
              allowPrivilegeEscalation: false
              capabilities:
                drop:
                  - ALL
        volumes:
        - name: all-in-one
          projected:
            sources:
            - secret:
                name: mysecret 1
      1
      The name of the secret you created.
    2. Create the pod from the configuration file:

      $ oc create -f <your_yaml_file>.yaml

      For example:

      $ oc create -f secret-pod.yaml

      Example output

      pod "test-projected-volume" created

  3. Verify that the pod container is running, and then watch for changes to the pod:

    $ oc get pod <name>

    For example:

    $ oc get pod test-projected-volume

    The output should appear similar to the following:

    Example output

    NAME                    READY     STATUS    RESTARTS   AGE
    test-projected-volume   1/1       Running   0          14s

  4. In another terminal, use the oc exec command to open a shell to the running container:

    $ oc exec -it <pod> <command>

    For example:

    $ oc exec -it test-projected-volume -- /bin/sh
  5. In your shell, verify that the projected-volumes directory contains your projected sources:

    / # ls

    Example output

    bin               home              root              tmp
    dev               proc              run               usr
    etc               projected-volume  sys               var

7.5. Allowing containers to consume API objects

The Downward API is a mechanism that allows containers to consume information about API objects without coupling to OpenShift Container Platform. Such information includes the pod’s name, namespace, and resource values. Containers can consume information from the downward API using environment variables or a volume plugin.

7.5.1. Expose pod information to Containers using the Downward API

The Downward API contains such information as the pod’s name, project, and resource values. Containers can consume information from the downward API using environment variables or a volume plugin.

Fields within the pod are selected using the FieldRef API type. FieldRef has two fields:

FieldDescription

fieldPath

The path of the field to select, relative to the pod.

apiVersion

The API version to interpret the fieldPath selector within.

Currently, the valid selectors in the v1 API include:

SelectorDescription

metadata.name

The pod’s name. This is supported in both environment variables and volumes.

metadata.namespace

The pod’s namespace.This is supported in both environment variables and volumes.

metadata.labels

The pod’s labels. This is only supported in volumes and not in environment variables.

metadata.annotations

The pod’s annotations. This is only supported in volumes and not in environment variables.

status.podIP

The pod’s IP. This is only supported in environment variables and not volumes.

The apiVersion field, if not specified, defaults to the API version of the enclosing pod template.

7.5.2. Understanding how to consume container values using the downward API

You containers can consume API values using environment variables or a volume plugin. Depending on the method you choose, containers can consume:

  • Pod name
  • Pod project/namespace
  • Pod annotations
  • Pod labels

Annotations and labels are available using only a volume plugin.

7.5.2.1. Consuming container values using environment variables

When using a container’s environment variables, use the EnvVar type’s valueFrom field (of type EnvVarSource) to specify that the variable’s value should come from a FieldRef source instead of the literal value specified by the value field.

Only constant attributes of the pod can be consumed this way, as environment variables cannot be updated once a process is started in a way that allows the process to be notified that the value of a variable has changed. The fields supported using environment variables are:

  • Pod name
  • Pod project/namespace

Procedure

  1. Create a new pod spec that contains the environment variables you want the container to consume:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: env-test-container
            image: gcr.io/google_containers/busybox
            command: [ "/bin/sh", "-c", "env" ]
            env:
              - name: MY_POD_NAME
                valueFrom:
                  fieldRef:
                    fieldPath: metadata.name
              - name: MY_POD_NAMESPACE
                valueFrom:
                  fieldRef:
                    fieldPath: metadata.namespace
        restartPolicy: Never
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml

Verification

  • Check the container’s logs for the MY_POD_NAME and MY_POD_NAMESPACE values:

    $ oc logs -p dapi-env-test-pod
7.5.2.2. Consuming container values using a volume plugin

You containers can consume API values using a volume plugin.

Containers can consume:

  • Pod name
  • Pod project/namespace
  • Pod annotations
  • Pod labels

Procedure

To use the volume plugin:

  1. Create a new pod spec that contains the environment variables you want the container to consume:

    1. Create a volume-pod.yaml file similar to the following:

      kind: Pod
      apiVersion: v1
      metadata:
        labels:
          zone: us-east-coast
          cluster: downward-api-test-cluster1
          rack: rack-123
        name: dapi-volume-test-pod
        annotations:
          annotation1: "345"
          annotation2: "456"
      spec:
        containers:
          - name: volume-test-container
            image: gcr.io/google_containers/busybox
            command: ["sh", "-c", "cat /tmp/etc/pod_labels /tmp/etc/pod_annotations"]
            volumeMounts:
              - name: podinfo
                mountPath: /tmp/etc
                readOnly: false
        volumes:
        - name: podinfo
          downwardAPI:
            defaultMode: 420
            items:
            - fieldRef:
                fieldPath: metadata.name
              path: pod_name
            - fieldRef:
                fieldPath: metadata.namespace
              path: pod_namespace
            - fieldRef:
                fieldPath: metadata.labels
              path: pod_labels
            - fieldRef:
                fieldPath: metadata.annotations
              path: pod_annotations
        restartPolicy: Never
      # ...
    2. Create the pod from the volume-pod.yaml file:

      $ oc create -f volume-pod.yaml

Verification

  • Check the container’s logs and verify the presence of the configured fields:

    $ oc logs -p dapi-volume-test-pod

    Example output

    cluster=downward-api-test-cluster1
    rack=rack-123
    zone=us-east-coast
    annotation1=345
    annotation2=456
    kubernetes.io/config.source=api

7.5.3. Understanding how to consume container resources using the Downward API

When creating pods, you can use the Downward API to inject information about computing resource requests and limits so that image and application authors can correctly create an image for specific environments.

You can do this using environment variable or a volume plugin.

7.5.3.1. Consuming container resources using environment variables

When creating pods, you can use the Downward API to inject information about computing resource requests and limits using environment variables.

When creating the pod configuration, specify environment variables that correspond to the contents of the resources field in the spec.container field.

Note

If the resource limits are not included in the container configuration, the downward API defaults to the node’s CPU and memory allocatable values.

Procedure

  1. Create a new pod spec that contains the resources you want to inject:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: test-container
            image: gcr.io/google_containers/busybox:1.24
            command: [ "/bin/sh", "-c", "env" ]
            resources:
              requests:
                memory: "32Mi"
                cpu: "125m"
              limits:
                memory: "64Mi"
                cpu: "250m"
            env:
              - name: MY_CPU_REQUEST
                valueFrom:
                  resourceFieldRef:
                    resource: requests.cpu
              - name: MY_CPU_LIMIT
                valueFrom:
                  resourceFieldRef:
                    resource: limits.cpu
              - name: MY_MEM_REQUEST
                valueFrom:
                  resourceFieldRef:
                    resource: requests.memory
              - name: MY_MEM_LIMIT
                valueFrom:
                  resourceFieldRef:
                    resource: limits.memory
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml
7.5.3.2. Consuming container resources using a volume plugin

When creating pods, you can use the Downward API to inject information about computing resource requests and limits using a volume plugin.

When creating the pod configuration, use the spec.volumes.downwardAPI.items field to describe the desired resources that correspond to the spec.resources field.

Note

If the resource limits are not included in the container configuration, the Downward API defaults to the node’s CPU and memory allocatable values.

Procedure

  1. Create a new pod spec that contains the resources you want to inject:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: client-container
            image: gcr.io/google_containers/busybox:1.24
            command: ["sh", "-c", "while true; do echo; if [[ -e /etc/cpu_limit ]]; then cat /etc/cpu_limit; fi; if [[ -e /etc/cpu_request ]]; then cat /etc/cpu_request; fi; if [[ -e /etc/mem_limit ]]; then cat /etc/mem_limit; fi; if [[ -e /etc/mem_request ]]; then cat /etc/mem_request; fi; sleep 5; done"]
            resources:
              requests:
                memory: "32Mi"
                cpu: "125m"
              limits:
                memory: "64Mi"
                cpu: "250m"
            volumeMounts:
              - name: podinfo
                mountPath: /etc
                readOnly: false
        volumes:
          - name: podinfo
            downwardAPI:
              items:
                - path: "cpu_limit"
                  resourceFieldRef:
                    containerName: client-container
                    resource: limits.cpu
                - path: "cpu_request"
                  resourceFieldRef:
                    containerName: client-container
                    resource: requests.cpu
                - path: "mem_limit"
                  resourceFieldRef:
                    containerName: client-container
                    resource: limits.memory
                - path: "mem_request"
                  resourceFieldRef:
                    containerName: client-container
                    resource: requests.memory
      # ...
    2. Create the pod from the volume-pod.yaml file:

      $ oc create -f volume-pod.yaml

7.5.4. Consuming secrets using the Downward API

When creating pods, you can use the downward API to inject secrets so image and application authors can create an image for specific environments.

Procedure

  1. Create a secret to inject:

    1. Create a secret.yaml file similar to the following:

      apiVersion: v1
      kind: Secret
      metadata:
        name: mysecret
      data:
        password: <password>
        username: <username>
      type: kubernetes.io/basic-auth
    2. Create the secret object from the secret.yaml file:

      $ oc create -f secret.yaml
  2. Create a pod that references the username field from the above Secret object:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: env-test-container
            image: gcr.io/google_containers/busybox
            command: [ "/bin/sh", "-c", "env" ]
            env:
              - name: MY_SECRET_USERNAME
                valueFrom:
                  secretKeyRef:
                    name: mysecret
                    key: username
        restartPolicy: Never
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml

Verification

  • Check the container’s logs for the MY_SECRET_USERNAME value:

    $ oc logs -p dapi-env-test-pod

7.5.5. Consuming configuration maps using the Downward API

When creating pods, you can use the Downward API to inject configuration map values so image and application authors can create an image for specific environments.

Procedure

  1. Create a config map with the values to inject:

    1. Create a configmap.yaml file similar to the following:

      apiVersion: v1
      kind: ConfigMap
      metadata:
        name: myconfigmap
      data:
        mykey: myvalue
    2. Create the config map from the configmap.yaml file:

      $ oc create -f configmap.yaml
  2. Create a pod that references the above config map:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: env-test-container
            image: gcr.io/google_containers/busybox
            command: [ "/bin/sh", "-c", "env" ]
            env:
              - name: MY_CONFIGMAP_VALUE
                valueFrom:
                  configMapKeyRef:
                    name: myconfigmap
                    key: mykey
        restartPolicy: Always
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml

Verification

  • Check the container’s logs for the MY_CONFIGMAP_VALUE value:

    $ oc logs -p dapi-env-test-pod

7.5.6. Referencing environment variables

When creating pods, you can reference the value of a previously defined environment variable by using the $() syntax. If the environment variable reference can not be resolved, the value will be left as the provided string.

Procedure

  1. Create a pod that references an existing environment variable:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: env-test-container
            image: gcr.io/google_containers/busybox
            command: [ "/bin/sh", "-c", "env" ]
            env:
              - name: MY_EXISTING_ENV
                value: my_value
              - name: MY_ENV_VAR_REF_ENV
                value: $(MY_EXISTING_ENV)
        restartPolicy: Never
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml

Verification

  • Check the container’s logs for the MY_ENV_VAR_REF_ENV value:

    $ oc logs -p dapi-env-test-pod

7.5.7. Escaping environment variable references

When creating a pod, you can escape an environment variable reference by using a double dollar sign. The value will then be set to a single dollar sign version of the provided value.

Procedure

  1. Create a pod that references an existing environment variable:

    1. Create a pod.yaml file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: dapi-env-test-pod
      spec:
        containers:
          - name: env-test-container
            image: gcr.io/google_containers/busybox
            command: [ "/bin/sh", "-c", "env" ]
            env:
              - name: MY_NEW_ENV
                value: $$(SOME_OTHER_ENV)
        restartPolicy: Never
      # ...
    2. Create the pod from the pod.yaml file:

      $ oc create -f pod.yaml

Verification

  • Check the container’s logs for the MY_NEW_ENV value:

    $ oc logs -p dapi-env-test-pod

7.6. Copying files to or from an OpenShift Container Platform container

You can use the CLI to copy local files to or from a remote directory in a container using the rsync command.

7.6.1. Understanding how to copy files

The oc rsync command, or remote sync, is a useful tool for copying database archives to and from your pods for backup and restore purposes. You can also use oc rsync to copy source code changes into a running pod for development debugging, when the running pod supports hot reload of source files.

$ oc rsync <source> <destination> [-c <container>]
7.6.1.1. Requirements
Specifying the Copy Source

The source argument of the oc rsync command must point to either a local directory or a pod directory. Individual files are not supported.

When specifying a pod directory the directory name must be prefixed with the pod name:

<pod name>:<dir>

If the directory name ends in a path separator (/), only the contents of the directory are copied to the destination. Otherwise, the directory and its contents are copied to the destination.

Specifying the Copy Destination
The destination argument of the oc rsync command must point to a directory. If the directory does not exist, but rsync is used for copy, the directory is created for you.
Deleting Files at the Destination
The --delete flag may be used to delete any files in the remote directory that are not in the local directory.
Continuous Syncing on File Change

Using the --watch option causes the command to monitor the source path for any file system changes, and synchronizes changes when they occur. With this argument, the command runs forever.

Synchronization occurs after short quiet periods to ensure a rapidly changing file system does not result in continuous synchronization calls.

When using the --watch option, the behavior is effectively the same as manually invoking oc rsync repeatedly, including any arguments normally passed to oc rsync. Therefore, you can control the behavior via the same flags used with manual invocations of oc rsync, such as --delete.

7.6.2. Copying files to and from containers

Support for copying local files to or from a container is built into the CLI.

Prerequisites

When working with oc rsync, note the following:

  • rsync must be installed. The oc rsync command uses the local rsync tool, if present on the client machine and the remote container.

    If rsync is not found locally or in the remote container, a tar archive is created locally and sent to the container where the tar utility is used to extract the files. If tar is not available in the remote container, the copy will fail.

    The tar copy method does not provide the same functionality as oc rsync. For example, oc rsync creates the destination directory if it does not exist and only sends files that are different between the source and the destination.

    Note

    In Windows, the cwRsync client should be installed and added to the PATH for use with the oc rsync command.

Procedure

  • To copy a local directory to a pod directory:

    $ oc rsync <local-dir> <pod-name>:/<remote-dir> -c <container-name>

    For example:

    $ oc rsync /home/user/source devpod1234:/src -c user-container
  • To copy a pod directory to a local directory:

    $ oc rsync devpod1234:/src /home/user/source

    Example output

    $ oc rsync devpod1234:/src/status.txt /home/user/

7.6.3. Using advanced Rsync features

The oc rsync command exposes fewer command line options than standard rsync. In the case that you want to use a standard rsync command line option that is not available in oc rsync, for example the --exclude-from=FILE option, it might be possible to use standard rsync 's --rsh (-e) option or RSYNC_RSH environment variable as a workaround, as follows:

$ rsync --rsh='oc rsh' --exclude-from=<file_name> <local-dir> <pod-name>:/<remote-dir>

or:

Export the RSYNC_RSH variable:

$ export RSYNC_RSH='oc rsh'

Then, run the rsync command:

$ rsync --exclude-from=<file_name> <local-dir> <pod-name>:/<remote-dir>

Both of the above examples configure standard rsync to use oc rsh as its remote shell program to enable it to connect to the remote pod, and are an alternative to running oc rsync.

7.7. Executing remote commands in an OpenShift Container Platform container

You can use the CLI to execute remote commands in an OpenShift Container Platform container.

7.7.1. Executing remote commands in containers

Support for remote container command execution is built into the CLI.

Procedure

To run a command in a container:

$ oc exec <pod> [-c <container>] -- <command> [<arg_1> ... <arg_n>]

For example:

$ oc exec mypod date

Example output

Thu Apr  9 02:21:53 UTC 2015

Important

For security purposes, the oc exec command does not work when accessing privileged containers except when the command is executed by a cluster-admin user.

7.7.2. Protocol for initiating a remote command from a client

Clients initiate the execution of a remote command in a container by issuing a request to the Kubernetes API server:

/proxy/nodes/<node_name>/exec/<namespace>/<pod>/<container>?command=<command>

In the above URL:

  • <node_name> is the FQDN of the node.
  • <namespace> is the project of the target pod.
  • <pod> is the name of the target pod.
  • <container> is the name of the target container.
  • <command> is the desired command to be executed.

For example:

/proxy/nodes/node123.openshift.com/exec/myns/mypod/mycontainer?command=date

Additionally, the client can add parameters to the request to indicate if:

  • the client should send input to the remote container’s command (stdin).
  • the client’s terminal is a TTY.
  • the remote container’s command should send output from stdout to the client.
  • the remote container’s command should send output from stderr to the client.

After sending an exec request to the API server, the client upgrades the connection to one that supports multiplexed streams; the current implementation uses HTTP/2.

The client creates one stream each for stdin, stdout, and stderr. To distinguish among the streams, the client sets the streamType header on the stream to one of stdin, stdout, or stderr.

The client closes all streams, the upgraded connection, and the underlying connection when it is finished with the remote command execution request.

7.8. Using port forwarding to access applications in a container

OpenShift Container Platform supports port forwarding to pods.

7.8.1. Understanding port forwarding

You can use the CLI to forward one or more local ports to a pod. This allows you to listen on a given or random port locally, and have data forwarded to and from given ports in the pod.

Support for port forwarding is built into the CLI:

$ oc port-forward <pod> [<local_port>:]<remote_port> [...[<local_port_n>:]<remote_port_n>]

The CLI listens on each local port specified by the user, forwarding using the protocol described below.

Ports may be specified using the following formats:

5000

The client listens on port 5000 locally and forwards to 5000 in the pod.

6000:5000

The client listens on port 6000 locally and forwards to 5000 in the pod.

:5000 or 0:5000

The client selects a free local port and forwards to 5000 in the pod.

OpenShift Container Platform handles port-forward requests from clients. Upon receiving a request, OpenShift Container Platform upgrades the response and waits for the client to create port-forwarding streams. When OpenShift Container Platform receives a new stream, it copies data between the stream and the pod’s port.

Architecturally, there are options for forwarding to a pod’s port. The supported OpenShift Container Platform implementation invokes nsenter directly on the node host to enter the pod’s network namespace, then invokes socat to copy data between the stream and the pod’s port. However, a custom implementation could include running a helper pod that then runs nsenter and socat, so that those binaries are not required to be installed on the host.

7.8.2. Using port forwarding

You can use the CLI to port-forward one or more local ports to a pod.

Procedure

Use the following command to listen on the specified port in a pod:

$ oc port-forward <pod> [<local_port>:]<remote_port> [...[<local_port_n>:]<remote_port_n>]

For example:

  • Use the following command to listen on ports 5000 and 6000 locally and forward data to and from ports 5000 and 6000 in the pod:

    $ oc port-forward <pod> 5000 6000

    Example output

    Forwarding from 127.0.0.1:5000 -> 5000
    Forwarding from [::1]:5000 -> 5000
    Forwarding from 127.0.0.1:6000 -> 6000
    Forwarding from [::1]:6000 -> 6000

  • Use the following command to listen on port 8888 locally and forward to 5000 in the pod:

    $ oc port-forward <pod> 8888:5000

    Example output

    Forwarding from 127.0.0.1:8888 -> 5000
    Forwarding from [::1]:8888 -> 5000

  • Use the following command to listen on a free port locally and forward to 5000 in the pod:

    $ oc port-forward <pod> :5000

    Example output

    Forwarding from 127.0.0.1:42390 -> 5000
    Forwarding from [::1]:42390 -> 5000

    Or:

    $ oc port-forward <pod> 0:5000

7.8.3. Protocol for initiating port forwarding from a client

Clients initiate port forwarding to a pod by issuing a request to the Kubernetes API server:

/proxy/nodes/<node_name>/portForward/<namespace>/<pod>

In the above URL:

  • <node_name> is the FQDN of the node.
  • <namespace> is the namespace of the target pod.
  • <pod> is the name of the target pod.

For example:

/proxy/nodes/node123.openshift.com/portForward/myns/mypod

After sending a port forward request to the API server, the client upgrades the connection to one that supports multiplexed streams; the current implementation uses Hyptertext Transfer Protocol Version 2 (HTTP/2).

The client creates a stream with the port header containing the target port in the pod. All data written to the stream is delivered via the kubelet to the target pod and port. Similarly, all data sent from the pod for that forwarded connection is delivered back to the same stream in the client.

The client closes all streams, the upgraded connection, and the underlying connection when it is finished with the port forwarding request.

7.9. Using sysctls in containers

Sysctl settings are exposed through Kubernetes, allowing users to modify certain kernel parameters at runtime. Only sysctls that are namespaced can be set independently on pods. If a sysctl is not namespaced, called node-level, you must use another method of setting the sysctl, such as by using the Node Tuning Operator.

Network sysctls are a special category of sysctl. Network sysctls include:

  • System-wide sysctls, for example net.ipv4.ip_local_port_range, that are valid for all networking. You can set these independently for each pod on a node.
  • Interface-specific sysctls, for example net.ipv4.conf.IFNAME.accept_local, that only apply to a specific additional network interface for a given pod. You can set these independently for each additional network configuration. You set these by using a configuration in the tuning-cni after the network interfaces are created.

Moreover, only those sysctls considered safe are whitelisted by default; you can manually enable other unsafe sysctls on the node to be available to the user.

Additional resources

If you are setting the sysctl and it is not node-level, you can find information on this procedure in the section Using the Node Tuning Operator.

7.9.1. About sysctls

In Linux, the sysctl interface allows an administrator to modify kernel parameters at runtime. Parameters are available from the /proc/sys/ virtual process file system. The parameters cover various subsystems, such as:

  • kernel (common prefix: kernel.)
  • networking (common prefix: net.)
  • virtual memory (common prefix: vm.)
  • MDADM (common prefix: dev.)

More subsystems are described in Kernel documentation. To get a list of all parameters, run:

$ sudo sysctl -a

7.9.2. Namespaced and node-level sysctls

A number of sysctls are namespaced in the Linux kernels. This means that you can set them independently for each pod on a node. Being namespaced is a requirement for sysctls to be accessible in a pod context within Kubernetes.

The following sysctls are known to be namespaced:

  • kernel.shm*
  • kernel.msg*
  • kernel.sem
  • fs.mqueue.*

Additionally, most of the sysctls in the net.* group are known to be namespaced. Their namespace adoption differs based on the kernel version and distributor.

Sysctls that are not namespaced are called node-level and must be set manually by the cluster administrator, either by means of the underlying Linux distribution of the nodes, such as by modifying the /etc/sysctls.conf file, or by using a daemon set with privileged containers. You can use the Node Tuning Operator to set node-level sysctls.

Note

Consider marking nodes with special sysctls as tainted. Only schedule pods onto them that need those sysctl settings. Use the taints and toleration feature to mark the nodes.

7.9.3. Safe and unsafe sysctls

Sysctls are grouped into safe and unsafe sysctls.

For system-wide sysctls to be considered safe, they must be namespaced. A namespaced sysctl ensures there is isolation between namespaces and therefore pods. If you set a sysctl for one pod it must not add any of the following:

  • Influence any other pod on the node
  • Harm the node health
  • Gain CPU or memory resources outside of the resource limits of a pod
Note

Being namespaced alone is not sufficient for the sysctl to be considered safe.

Any sysctl that is not added to the allowed list on OpenShift Container Platform is considered unsafe for OpenShift Container Platform.

Unsafe sysctls are not allowed by default. For system-wide sysctls the cluster administrator must manually enable them on a per-node basis. Pods with disabled unsafe sysctls are scheduled but do not launch.

Note

You cannot manually enable interface-specific unsafe sysctls.

OpenShift Container Platform adds the following system-wide and interface-specific safe sysctls to an allowed safe list:

Table 7.4. System-wide safe sysctls
sysctlDescription

kernel.shm_rmid_forced

When set to 1, all shared memory objects in current IPC namespace are automatically forced to use IPC_RMID. For more information, see shm_rmid_forced.

net.ipv4.ip_local_port_range

Defines the local port range that is used by TCP and UDP to choose the local port. The first number is the first port number, and the second number is the last local port number. If possible, it is better if these numbers have different parity (one even and one odd value). They must be greater than or equal to ip_unprivileged_port_start. The default values are 32768 and 60999 respectively. For more information, see ip_local_port_range.

net.ipv4.tcp_syncookies

When net.ipv4.tcp_syncookies is set, the kernel handles TCP SYN packets normally until the half-open connection queue is full, at which time, the SYN cookie functionality kicks in. This functionality allows the system to keep accepting valid connections, even if under a denial-of-service attack. For more information, see tcp_syncookies.

net.ipv4.ping_group_range

This restricts ICMP_PROTO datagram sockets to users in the group range. The default is 1 0, meaning that nobody, not even root, can create ping sockets. For more information, see ping_group_range.

net.ipv4.ip_unprivileged_port_start

This defines the first unprivileged port in the network namespace. To disable all privileged ports, set this to 0. Privileged ports must not overlap with the ip_local_port_range. For more information, see ip_unprivileged_port_start.

Table 7.5. Interface-specific safe sysctls
sysctlDescription

net.ipv4.conf.IFNAME.accept_redirects

Accept IPv4 ICMP redirect messages.

net.ipv4.conf.IFNAME.accept_source_route

Accept IPv4 packets with strict source route (SRR) option.

net.ipv4.conf.IFNAME.arp_accept

Define behavior for gratuitous ARP frames with an IPv4 address that is not already present in the ARP table:

  • 0 - Do not create new entries in the ARP table.
  • 1 - Create new entries in the ARP table.

net.ipv4.conf.IFNAME.arp_notify

Define mode for notification of IPv4 address and device changes.

net.ipv4.conf.IFNAME.disable_policy

Disable IPSEC policy (SPD) for this IPv4 interface.

net.ipv4.conf.IFNAME.secure_redirects

Accept ICMP redirect messages only to gateways listed in the interface’s current gateway list.

net.ipv4.conf.IFNAME.send_redirects

Send redirects is enabled only if the node acts as a router. That is, a host should not send an ICMP redirect message. It is used by routers to notify the host about a better routing path that is available for a particular destination.

net.ipv6.conf.IFNAME.accept_ra

Accept IPv6 Router advertisements; autoconfigure using them. It also determines whether or not to transmit router solicitations. Router solicitations are transmitted only if the functional setting is to accept router advertisements.

net.ipv6.conf.IFNAME.accept_redirects

Accept IPv6 ICMP redirect messages.

net.ipv6.conf.IFNAME.accept_source_route

Accept IPv6 packets with SRR option.

net.ipv6.conf.IFNAME.arp_accept

Define behavior for gratuitous ARP frames with an IPv6 address that is not already present in the ARP table:

  • 0 - Do not create new entries in the ARP table.
  • 1 - Create new entries in the ARP table.

net.ipv6.conf.IFNAME.arp_notify

Define mode for notification of IPv6 address and device changes.

net.ipv6.neigh.IFNAME.base_reachable_time_ms

This parameter controls the hardware address to IP mapping lifetime in the neighbour table for IPv6.

net.ipv6.neigh.IFNAME.retrans_time_ms

Set the retransmit timer for neighbor discovery messages.

Note

When setting these values using the tuning CNI plugin, use the value IFNAME literally. The interface name is represented by the IFNAME token, and is replaced with the actual name of the interface at runtime.

7.9.4. Updating the interface-specific safe sysctls list

OpenShift Container Platform includes a predefined list of safe interface-specific sysctls. You can modify this list by updating the cni-sysctl-allowlist in the openshift-multus namespace.

Important

The support for updating the interface-specific safe sysctls list is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

Follow this procedure to modify the predefined list of safe sysctls. This procedure describes how to extend the default allow list.

Procedure

  1. View the existing predefined list by running the following command:

    $ oc get cm -n openshift-multus cni-sysctl-allowlist -oyaml

    Expected output

    apiVersion: v1
    data:
      allowlist.conf: |-
        ^net.ipv4.conf.IFNAME.accept_redirects$
        ^net.ipv4.conf.IFNAME.accept_source_route$
        ^net.ipv4.conf.IFNAME.arp_accept$
        ^net.ipv4.conf.IFNAME.arp_notify$
        ^net.ipv4.conf.IFNAME.disable_policy$
        ^net.ipv4.conf.IFNAME.secure_redirects$
        ^net.ipv4.conf.IFNAME.send_redirects$
        ^net.ipv6.conf.IFNAME.accept_ra$
        ^net.ipv6.conf.IFNAME.accept_redirects$
        ^net.ipv6.conf.IFNAME.accept_source_route$
        ^net.ipv6.conf.IFNAME.arp_accept$
        ^net.ipv6.conf.IFNAME.arp_notify$
        ^net.ipv6.neigh.IFNAME.base_reachable_time_ms$
        ^net.ipv6.neigh.IFNAME.retrans_time_ms$
    kind: ConfigMap
    metadata:
      annotations:
        kubernetes.io/description: |
          Sysctl allowlist for nodes.
        release.openshift.io/version: 4.12.0-0.nightly-2022-11-16-003434
      creationTimestamp: "2022-11-17T14:09:27Z"
      name: cni-sysctl-allowlist
      namespace: openshift-multus
      resourceVersion: "2422"
      uid: 96d138a3-160e-4943-90ff-6108fa7c50c3

  2. Edit the list by using the following command:

    $ oc edit cm -n openshift-multus cni-sysctl-allowlist -oyaml

    For example, to allow you to be able to implement stricter reverse path forwarding you need to add ^net.ipv4.conf.IFNAME.rp_filter$ and ^net.ipv6.conf.IFNAME.rp_filter$ to the list as shown here:

    # Please edit the object below. Lines beginning with a '#' will be ignored,
    # and an empty file will abort the edit. If an error occurs while saving this file will be
    # reopened with the relevant failures.
    #
    apiVersion: v1
    data:
      allowlist.conf: |-
        ^net.ipv4.conf.IFNAME.accept_redirects$
        ^net.ipv4.conf.IFNAME.accept_source_route$
        ^net.ipv4.conf.IFNAME.arp_accept$
        ^net.ipv4.conf.IFNAME.arp_notify$
        ^net.ipv4.conf.IFNAME.disable_policy$
        ^net.ipv4.conf.IFNAME.secure_redirects$
        ^net.ipv4.conf.IFNAME.send_redirects$
        ^net.ipv4.conf.IFNAME.rp_filter$
        ^net.ipv6.conf.IFNAME.accept_ra$
        ^net.ipv6.conf.IFNAME.accept_redirects$
        ^net.ipv6.conf.IFNAME.accept_source_route$
        ^net.ipv6.conf.IFNAME.arp_accept$
        ^net.ipv6.conf.IFNAME.arp_notify$
        ^net.ipv6.neigh.IFNAME.base_reachable_time_ms$
        ^net.ipv6.neigh.IFNAME.retrans_time_ms$
        ^net.ipv6.conf.IFNAME.rp_filter$
  3. Save the changes to the file and exit.

    Note

    The removal of sysctls is also supported. Edit the file, remove the sysctl or sysctls then save the changes and exit.

Verification

Follow this procedure to enforce stricter reverse path forwarding for IPv4. For more information on reverse path forwarding see Reverse Path Forwarding .

  1. Create a network attachment definition, such as reverse-path-fwd-example.yaml, with the following content:

    apiVersion: "k8s.cni.cncf.io/v1"
    kind: NetworkAttachmentDefinition
    metadata:
      name: tuningnad
      namespace: default
    spec:
      config: '{
        "cniVersion": "0.4.0",
        "name": "tuningnad",
        "plugins": [{
          "type": "bridge"
          },
          {
          "type": "tuning",
          "sysctl": {
             "net.ipv4.conf.IFNAME.rp_filter": "1"
            }
        }
      ]
    }'
  2. Apply the yaml by running the following command:

    $ oc apply -f reverse-path-fwd-example.yaml

    Example output

    networkattachmentdefinition.k8.cni.cncf.io/tuningnad created

  3. Create a pod such as examplepod.yaml using the following YAML:

    apiVersion: v1
    kind: Pod
    metadata:
      name: example
      labels:
        app: httpd
      namespace: default
      annotations:
        k8s.v1.cni.cncf.io/networks: tuningnad  1
    spec:
      securityContext:
        runAsNonRoot: true
        seccompProfile:
          type: RuntimeDefault
      containers:
        - name: httpd
          image: 'image-registry.openshift-image-registry.svc:5000/openshift/httpd:latest'
          ports:
            - containerPort: 8080
          securityContext:
            allowPrivilegeEscalation: false
            capabilities:
              drop:
                - ALL
    1
    Specify the name of the configured NetworkAttachmentDefinition.
  4. Apply the yaml by running the following command:

    $ oc apply -f examplepod.yaml
  5. Verify that the pod is created by running the following command:

    $ oc get pod

    Example output

    NAME      READY   STATUS    RESTARTS   AGE
    example   1/1     Running   0          47s

  6. Log in to the pod by running the following command:

    $ oc rsh example
  7. Verify the value of the configured sysctl flag. For example, find the value net.ipv4.conf.net1.rp_filter by running the following command:

    sh-4.4# sysctl net.ipv4.conf.net1.rp_filter

    Expected output

    net.ipv4.conf.net1.rp_filter = 1

7.9.5. Starting a pod with safe sysctls

You can set sysctls on pods using the pod’s securityContext. The securityContext applies to all containers in the same pod.

Safe sysctls are allowed by default.

This example uses the pod securityContext to set the following safe sysctls:

  • kernel.shm_rmid_forced
  • net.ipv4.ip_local_port_range
  • net.ipv4.tcp_syncookies
  • net.ipv4.ping_group_range
Warning

To avoid destabilizing your operating system, modify sysctl parameters only after you understand their effects.

Use this procedure to start a pod with the configured sysctl settings.

Note

In most cases you modify an existing pod definition and add the securityContext spec.

Procedure

  1. Create a YAML file sysctl_pod.yaml that defines an example pod and add the securityContext spec, as shown in the following example:

    apiVersion: v1
    kind: Pod
    metadata:
      name: sysctl-example
      namespace: default
    spec:
      containers:
      - name: podexample
        image: centos
        command: ["bin/bash", "-c", "sleep INF"]
        securityContext:
          runAsUser: 2000 1
          runAsGroup: 3000 2
          allowPrivilegeEscalation: false 3
          capabilities: 4
            drop: ["ALL"]
      securityContext:
        runAsNonRoot: true 5
        seccompProfile: 6
          type: RuntimeDefault
        sysctls:
        - name: kernel.shm_rmid_forced
          value: "1"
        - name: net.ipv4.ip_local_port_range
          value: "32770       60666"
        - name: net.ipv4.tcp_syncookies
          value: "0"
        - name: net.ipv4.ping_group_range
          value: "0           200000000"
    1
    runAsUser controls which user ID the container is run with.
    2
    runAsGroup controls which primary group ID the containers is run with.
    3
    allowPrivilegeEscalation determines if a pod can request to allow privilege escalation. If unspecified, it defaults to true. This boolean directly controls whether the no_new_privs flag gets set on the container process.
    4
    capabilities permit privileged actions without giving full root access. This policy ensures all capabilities are dropped from the pod.
    5
    runAsNonRoot: true requires that the container will run with a user with any UID other than 0.
    6
    RuntimeDefault enables the default seccomp profile for a pod or container workload.
  2. Create the pod by running the following command:

    $ oc apply -f sysctl_pod.yaml
  3. Verify that the pod is created by running the following command:

    $ oc get pod

    Example output

    NAME              READY   STATUS            RESTARTS   AGE
    sysctl-example    1/1     Running           0          14s

  4. Log in to the pod by running the following command:

    $ oc rsh sysctl-example
  5. Verify the values of the configured sysctl flags. For example, find the value kernel.shm_rmid_forced by running the following command:

    sh-4.4# sysctl kernel.shm_rmid_forced

    Expected output

    kernel.shm_rmid_forced = 1

7.9.6. Starting a pod with unsafe sysctls

A pod with unsafe sysctls fails to launch on any node unless the cluster administrator explicitly enables unsafe sysctls for that node. As with node-level sysctls, use the taints and toleration feature or labels on nodes to schedule those pods onto the right nodes.

The following example uses the pod securityContext to set a safe sysctl kernel.shm_rmid_forced and two unsafe sysctls, net.core.somaxconn and kernel.msgmax. There is no distinction between safe and unsafe sysctls in the specification.

Warning

To avoid destabilizing your operating system, modify sysctl parameters only after you understand their effects.

The following example illustrates what happens when you add safe and unsafe sysctls to a pod specification:

Procedure

  1. Create a YAML file sysctl-example-unsafe.yaml that defines an example pod and add the securityContext specification, as shown in the following example:

    apiVersion: v1
    kind: Pod
    metadata:
      name: sysctl-example-unsafe
    spec:
      containers:
      - name: podexample
        image: centos
        command: ["bin/bash", "-c", "sleep INF"]
        securityContext:
          runAsUser: 2000
          runAsGroup: 3000
          allowPrivilegeEscalation: false
          capabilities:
            drop: ["ALL"]
      securityContext:
        runAsNonRoot: true
        seccompProfile:
          type: RuntimeDefault
        sysctls:
        - name: kernel.shm_rmid_forced
          value: "0"
        - name: net.core.somaxconn
          value: "1024"
        - name: kernel.msgmax
          value: "65536"
  2. Create the pod using the following command:

    $ oc apply -f sysctl-example-unsafe.yaml
  3. Verify that the pod is scheduled but does not deploy because unsafe sysctls are not allowed for the node using the following command:

    $ oc get pod

    Example output

    NAME                       READY             STATUS            RESTARTS   AGE
    sysctl-example-unsafe      0/1               SysctlForbidden   0          14s

7.9.7. Enabling unsafe sysctls

A cluster administrator can allow certain unsafe sysctls for very special situations such as high performance or real-time application tuning.

If you want to use unsafe sysctls, a cluster administrator must enable them individually for a specific type of node. The sysctls must be namespaced.

You can further control which sysctls are set in pods by specifying lists of sysctls or sysctl patterns in the allowedUnsafeSysctls field of the Security Context Constraints.

  • The allowedUnsafeSysctls option controls specific needs such as high performance or real-time application tuning.
Warning

Due to their nature of being unsafe, the use of unsafe sysctls is at-your-own-risk and can lead to severe problems, such as improper behavior of containers, resource shortage, or breaking a node.

Procedure

  1. List existing MachineConfig objects for your OpenShift Container Platform cluster to decide how to label your machine config by running the following command:

    $ oc get machineconfigpool

    Example output

    NAME     CONFIG                                             UPDATED   UPDATING   DEGRADED   MACHINECOUNT   READYMACHINECOUNT   UPDATEDMACHINECOUNT   DEGRADEDMACHINECOUNT   AGE
    master   rendered-master-bfb92f0cd1684e54d8e234ab7423cc96   True      False      False      3              3                   3                     0                      42m
    worker   rendered-worker-21b6cb9a0f8919c88caf39db80ac1fce   True      False      False      3              3                   3                     0                      42m

  2. Add a label to the machine config pool where the containers with the unsafe sysctls will run by running the following command:

    $ oc label machineconfigpool worker custom-kubelet=sysctl
  3. Create a YAML file set-sysctl-worker.yaml that defines a KubeletConfig custom resource (CR):

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: custom-kubelet
    spec:
      machineConfigPoolSelector:
        matchLabels:
          custom-kubelet: sysctl 1
      kubeletConfig:
        allowedUnsafeSysctls: 2
          - "kernel.msg*"
          - "net.core.somaxconn"
    1
    Specify the label from the machine config pool.
    2
    List the unsafe sysctls you want to allow.
  4. Create the object by running the following command:

    $ oc apply -f set-sysctl-worker.yaml
  5. Wait for the Machine Config Operator to generate the new rendered configuration and apply it to the machines by running the following command:

    $ oc get machineconfigpool worker -w

    After some minutes the UPDATING status changes from True to False:

    NAME     CONFIG                                             UPDATED   UPDATING   DEGRADED   MACHINECOUNT   READYMACHINECOUNT   UPDATEDMACHINECOUNT   DEGRADEDMACHINECOUNT   AGE
    worker   rendered-worker-f1704a00fc6f30d3a7de9a15fd68a800   False     True       False      3              2                   2                     0                      71m
    worker   rendered-worker-f1704a00fc6f30d3a7de9a15fd68a800   False     True       False      3              2                   3                     0                      72m
    worker   rendered-worker-0188658afe1f3a183ec8c4f14186f4d5   True      False      False      3              3                   3                     0                      72m
  6. Create a YAML file sysctl-example-safe-unsafe.yaml that defines an example pod and add the securityContext spec, as shown in the following example:

    apiVersion: v1
    kind: Pod
    metadata:
      name: sysctl-example-safe-unsafe
    spec:
      containers:
      - name: podexample
        image: centos
        command: ["bin/bash", "-c", "sleep INF"]
        securityContext:
          runAsUser: 2000
          runAsGroup: 3000
          allowPrivilegeEscalation: false
          capabilities:
            drop: ["ALL"]
      securityContext:
        runAsNonRoot: true
        seccompProfile:
          type: RuntimeDefault
        sysctls:
        - name: kernel.shm_rmid_forced
          value: "0"
        - name: net.core.somaxconn
          value: "1024"
        - name: kernel.msgmax
          value: "65536"
  7. Create the pod by running the following command:

    $ oc apply -f sysctl-example-safe-unsafe.yaml

    Expected output

    Warning: would violate PodSecurity "restricted:latest": forbidden sysctls (net.core.somaxconn, kernel.msgmax)
    pod/sysctl-example-safe-unsafe created

  8. Verify that the pod is created by running the following command:

    $ oc get pod

    Example output

    NAME                         READY   STATUS    RESTARTS   AGE
    sysctl-example-safe-unsafe   1/1     Running   0          19s

  9. Log in to the pod by running the following command:

    $ oc rsh sysctl-example-safe-unsafe
  10. Verify the values of the configured sysctl flags. For example, find the value net.core.somaxconn by running the following command:

    sh-4.4# sysctl net.core.somaxconn

    Expected output

    net.core.somaxconn = 1024

The unsafe sysctl is now allowed and the value is set as defined in the securityContext spec of the updated pod specification.

7.9.8. Additional resources

Chapter 8. Working with clusters

8.1. Viewing system event information in an OpenShift Container Platform cluster

Events in OpenShift Container Platform are modeled based on events that happen to API objects in an OpenShift Container Platform cluster.

8.1.1. Understanding events

Events allow OpenShift Container Platform to record information about real-world events in a resource-agnostic manner. They also allow developers and administrators to consume information about system components in a unified way.

8.1.2. Viewing events using the CLI

You can get a list of events in a given project using the CLI.

Procedure

  • To view events in a project use the following command:

    $ oc get events [-n <project>] 1
    1
    The name of the project.

    For example:

    $ oc get events -n openshift-config

    Example output

    LAST SEEN   TYPE      REASON                   OBJECT                      MESSAGE
    97m         Normal    Scheduled                pod/dapi-env-test-pod       Successfully assigned openshift-config/dapi-env-test-pod to ip-10-0-171-202.ec2.internal
    97m         Normal    Pulling                  pod/dapi-env-test-pod       pulling image "gcr.io/google_containers/busybox"
    97m         Normal    Pulled                   pod/dapi-env-test-pod       Successfully pulled image "gcr.io/google_containers/busybox"
    97m         Normal    Created                  pod/dapi-env-test-pod       Created container
    9m5s        Warning   FailedCreatePodSandBox   pod/dapi-volume-test-pod    Failed create pod sandbox: rpc error: code = Unknown desc = failed to create pod network sandbox k8s_dapi-volume-test-pod_openshift-config_6bc60c1f-452e-11e9-9140-0eec59c23068_0(748c7a40db3d08c07fb4f9eba774bd5effe5f0d5090a242432a73eee66ba9e22): Multus: Err adding pod to network "openshift-sdn": cannot set "openshift-sdn" ifname to "eth0": no netns: failed to Statfs "/proc/33366/ns/net": no such file or directory
    8m31s       Normal    Scheduled                pod/dapi-volume-test-pod    Successfully assigned openshift-config/dapi-volume-test-pod to ip-10-0-171-202.ec2.internal

  • To view events in your project from the OpenShift Container Platform console.

    1. Launch the OpenShift Container Platform console.
    2. Click HomeEvents and select your project.
    3. Move to resource that you want to see events. For example: HomeProjects → <project-name> → <resource-name>.

      Many objects, such as pods and deployments, have their own Events tab as well, which shows events related to that object.

8.1.3. List of events

This section describes the events of OpenShift Container Platform.

Table 8.1. Configuration events
NameDescription

FailedValidation

Failed pod configuration validation.

Table 8.2. Container events
NameDescription

BackOff

Back-off restarting failed the container.

Created

Container created.

Failed

Pull/Create/Start failed.

Killing

Killing the container.

Started

Container started.

Preempting

Preempting other pods.

ExceededGracePeriod

Container runtime did not stop the pod within specified grace period.

Table 8.3. Health events
NameDescription

Unhealthy

Container is unhealthy.

Table 8.4. Image events
NameDescription

BackOff

Back off Ctr Start, image pull.

ErrImageNeverPull

The image’s NeverPull Policy is violated.

Failed

Failed to pull the image.

InspectFailed

Failed to inspect the image.

Pulled

Successfully pulled the image or the container image is already present on the machine.

Pulling

Pulling the image.

Table 8.5. Image Manager events
NameDescription

FreeDiskSpaceFailed

Free disk space failed.

InvalidDiskCapacity

Invalid disk capacity.

Table 8.6. Node events
NameDescription

FailedMount

Volume mount failed.

HostNetworkNotSupported

Host network not supported.

HostPortConflict

Host/port conflict.

KubeletSetupFailed

Kubelet setup failed.

NilShaper

Undefined shaper.

NodeNotReady

Node is not ready.

NodeNotSchedulable

Node is not schedulable.

NodeReady

Node is ready.

NodeSchedulable

Node is schedulable.

NodeSelectorMismatching

Node selector mismatch.

OutOfDisk

Out of disk.

Rebooted

Node rebooted.

Starting

Starting kubelet.

FailedAttachVolume

Failed to attach volume.

FailedDetachVolume

Failed to detach volume.

VolumeResizeFailed

Failed to expand/reduce volume.

VolumeResizeSuccessful

Successfully expanded/reduced volume.

FileSystemResizeFailed

Failed to expand/reduce file system.

FileSystemResizeSuccessful

Successfully expanded/reduced file system.

FailedUnMount

Failed to unmount volume.

FailedMapVolume

Failed to map a volume.

FailedUnmapDevice

Failed unmaped device.

AlreadyMountedVolume

Volume is already mounted.

SuccessfulDetachVolume

Volume is successfully detached.

SuccessfulMountVolume

Volume is successfully mounted.

SuccessfulUnMountVolume

Volume is successfully unmounted.

ContainerGCFailed

Container garbage collection failed.

ImageGCFailed

Image garbage collection failed.

FailedNodeAllocatableEnforcement

Failed to enforce System Reserved Cgroup limit.

NodeAllocatableEnforced

Enforced System Reserved Cgroup limit.

UnsupportedMountOption

Unsupported mount option.

SandboxChanged

Pod sandbox changed.

FailedCreatePodSandBox

Failed to create pod sandbox.

FailedPodSandBoxStatus

Failed pod sandbox status.

Table 8.7. Pod worker events
NameDescription

FailedSync

Pod sync failed.

Table 8.8. System Events
NameDescription

SystemOOM

There is an OOM (out of memory) situation on the cluster.

Table 8.9. Pod events
NameDescription

FailedKillPod

Failed to stop a pod.

FailedCreatePodContainer

Failed to create a pod container.

Failed

Failed to make pod data directories.

NetworkNotReady

Network is not ready.

FailedCreate

Error creating: <error-msg>.

SuccessfulCreate

Created pod: <pod-name>.

FailedDelete

Error deleting: <error-msg>.

SuccessfulDelete

Deleted pod: <pod-id>.

Table 8.10. Horizontal Pod AutoScaler events
NameDescription

SelectorRequired

Selector is required.

InvalidSelector

Could not convert selector into a corresponding internal selector object.

FailedGetObjectMetric

HPA was unable to compute the replica count.

InvalidMetricSourceType

Unknown metric source type.

ValidMetricFound

HPA was able to successfully calculate a replica count.

FailedConvertHPA

Failed to convert the given HPA.

FailedGetScale

HPA controller was unable to get the target’s current scale.

SucceededGetScale

HPA controller was able to get the target’s current scale.

FailedComputeMetricsReplicas

Failed to compute desired number of replicas based on listed metrics.

FailedRescale

New size: <size>; reason: <msg>; error: <error-msg>.

SuccessfulRescale

New size: <size>; reason: <msg>.

FailedUpdateStatus

Failed to update status.

Table 8.11. Network events (openshift-sdn)
NameDescription

Starting

Starting OpenShift SDN.

NetworkFailed

The pod’s network interface has been lost and the pod will be stopped.

Table 8.12. Network events (kube-proxy)
NameDescription

NeedPods

The service-port <serviceName>:<port> needs pods.

Table 8.13. Volume events
NameDescription

FailedBinding

There are no persistent volumes available and no storage class is set.

VolumeMismatch

Volume size or class is different from what is requested in claim.

VolumeFailedRecycle

Error creating recycler pod.

VolumeRecycled

Occurs when volume is recycled.

RecyclerPod

Occurs when pod is recycled.

VolumeDelete

Occurs when volume is deleted.

VolumeFailedDelete

Error when deleting the volume.

ExternalProvisioning

Occurs when volume for the claim is provisioned either manually or via external software.

ProvisioningFailed

Failed to provision volume.

ProvisioningCleanupFailed

Error cleaning provisioned volume.

ProvisioningSucceeded

Occurs when the volume is provisioned successfully.

WaitForFirstConsumer

Delay binding until pod scheduling.

Table 8.14. Lifecycle hooks
NameDescription

FailedPostStartHook

Handler failed for pod start.

FailedPreStopHook

Handler failed for pre-stop.

UnfinishedPreStopHook

Pre-stop hook unfinished.

Table 8.15. Deployments
NameDescription

DeploymentCancellationFailed

Failed to cancel deployment.

DeploymentCancelled

Canceled deployment.

DeploymentCreated

Created new replication controller.

IngressIPRangeFull

No available Ingress IP to allocate to service.

Table 8.16. Scheduler events
NameDescription

FailedScheduling

Failed to schedule pod: <pod-namespace>/<pod-name>. This event is raised for multiple reasons, for example: AssumePodVolumes failed, Binding rejected etc.

Preempted

By <preemptor-namespace>/<preemptor-name> on node <node-name>.

Scheduled

Successfully assigned <pod-name> to <node-name>.

Table 8.17. Daemon set events
NameDescription

SelectingAll

This daemon set is selecting all pods. A non-empty selector is required.

FailedPlacement

Failed to place pod on <node-name>.

FailedDaemonPod

Found failed daemon pod <pod-name> on node <node-name>, will try to kill it.

Table 8.18. LoadBalancer service events
NameDescription

CreatingLoadBalancerFailed

Error creating load balancer.

DeletingLoadBalancer

Deleting load balancer.

EnsuringLoadBalancer

Ensuring load balancer.

EnsuredLoadBalancer

Ensured load balancer.

UnAvailableLoadBalancer

There are no available nodes for LoadBalancer service.

LoadBalancerSourceRanges

Lists the new LoadBalancerSourceRanges. For example, <old-source-range> → <new-source-range>.

LoadbalancerIP

Lists the new IP address. For example, <old-ip> → <new-ip>.

ExternalIP

Lists external IP address. For example, Added: <external-ip>.

UID

Lists the new UID. For example, <old-service-uid> → <new-service-uid>.

ExternalTrafficPolicy

Lists the new ExternalTrafficPolicy. For example, <old-policy> → <new-policy>.

HealthCheckNodePort

Lists the new HealthCheckNodePort. For example, <old-node-port> → new-node-port>.

UpdatedLoadBalancer

Updated load balancer with new hosts.

LoadBalancerUpdateFailed

Error updating load balancer with new hosts.

DeletingLoadBalancer

Deleting load balancer.

DeletingLoadBalancerFailed

Error deleting load balancer.

DeletedLoadBalancer

Deleted load balancer.

8.2. Estimating the number of pods your OpenShift Container Platform nodes can hold

As a cluster administrator, you can use the OpenShift Cluster Capacity Tool to view the number of pods that can be scheduled to increase the current resources before they become exhausted, and to ensure any future pods can be scheduled. This capacity comes from an individual node host in a cluster, and includes CPU, memory, disk space, and others.

8.2.1. Understanding the OpenShift Cluster Capacity Tool

The OpenShift Cluster Capacity Tool simulates a sequence of scheduling decisions to determine how many instances of an input pod can be scheduled on the cluster before it is exhausted of resources to provide a more accurate estimation.

Note

The remaining allocatable capacity is a rough estimation, because it does not count all of the resources being distributed among nodes. It analyzes only the remaining resources and estimates the available capacity that is still consumable in terms of a number of instances of a pod with given requirements that can be scheduled in a cluster.

Also, pods might only have scheduling support on particular sets of nodes based on its selection and affinity criteria. As a result, the estimation of which remaining pods a cluster can schedule can be difficult.

You can run the OpenShift Cluster Capacity Tool as a stand-alone utility from the command line, or as a job in a pod inside an OpenShift Container Platform cluster. Running the tool as job inside of a pod enables you to run it multiple times without intervention.

8.2.2. Running the OpenShift Cluster Capacity Tool on the command line

You can run the OpenShift Cluster Capacity Tool from the command line to estimate the number of pods that can be scheduled onto your cluster.

You create a sample pod spec file, which the tool uses for estimating resource usage. The pod spec specifies its resource requirements as limits or requests. The cluster capacity tool takes the pod’s resource requirements into account for its estimation analysis.

Prerequisites

  1. Run the OpenShift Cluster Capacity Tool, which is available as a container image from the Red Hat Ecosystem Catalog.
  2. Create a sample pod spec file:

    1. Create a YAML file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: small-pod
        labels:
          app: guestbook
          tier: frontend
      spec:
        containers:
        - name: php-redis
          image: gcr.io/google-samples/gb-frontend:v4
          imagePullPolicy: Always
          resources:
            limits:
              cpu: 150m
              memory: 100Mi
            requests:
              cpu: 150m
              memory: 100Mi
    2. Create the cluster role:

      $ oc create -f <file_name>.yaml

      For example:

      $ oc create -f pod-spec.yaml

Procedure

To use the cluster capacity tool on the command line:

  1. From the terminal, log in to the Red Hat Registry:

    $ podman login registry.redhat.io
  2. Pull the cluster capacity tool image:

    $ podman pull registry.redhat.io/openshift4/ose-cluster-capacity
  3. Run the cluster capacity tool:

    $ podman run -v $HOME/.kube:/kube:Z -v $(pwd):/cc:Z  ose-cluster-capacity \
    /bin/cluster-capacity --kubeconfig /kube/config --<pod_spec>.yaml /cc/<pod_spec>.yaml \
    --verbose

    where:

    <pod_spec>.yaml
    Specifies the pod spec to use.
    verbose
    Outputs a detailed description of how many pods can be scheduled on each node in the cluster.

    Example output

    small-pod pod requirements:
    	- CPU: 150m
    	- Memory: 100Mi
    
    The cluster can schedule 88 instance(s) of the pod small-pod.
    
    Termination reason: Unschedulable: 0/5 nodes are available: 2 Insufficient cpu,
    3 node(s) had taint {node-role.kubernetes.io/master: }, that the pod didn't
    tolerate.
    
    Pod distribution among nodes:
    small-pod
    	- 192.168.124.214: 45 instance(s)
    	- 192.168.124.120: 43 instance(s)

    In the above example, the number of estimated pods that can be scheduled onto the cluster is 88.

8.2.3. Running the OpenShift Cluster Capacity Tool as a job inside a pod

Running the OpenShift Cluster Capacity Tool as a job inside of a pod allows you to run the tool multiple times without needing user intervention. You run the OpenShift Cluster Capacity Tool as a job by using a ConfigMap object.

Prerequisites

Download and install OpenShift Cluster Capacity Tool.

Procedure

To run the cluster capacity tool:

  1. Create the cluster role:

    1. Create a YAML file similar to the following:

      kind: ClusterRole
      apiVersion: rbac.authorization.k8s.io/v1
      metadata:
        name: cluster-capacity-role
      rules:
      - apiGroups: [""]
        resources: ["pods", "nodes", "persistentvolumeclaims", "persistentvolumes", "services", "replicationcontrollers"]
        verbs: ["get", "watch", "list"]
      - apiGroups: ["apps"]
        resources: ["replicasets", "statefulsets"]
        verbs: ["get", "watch", "list"]
      - apiGroups: ["policy"]
        resources: ["poddisruptionbudgets"]
        verbs: ["get", "watch", "list"]
      - apiGroups: ["storage.k8s.io"]
        resources: ["storageclasses"]
        verbs: ["get", "watch", "list"]
    2. Create the cluster role by running the following command:

      $ oc create -f <file_name>.yaml

      For example:

      $ oc create sa cluster-capacity-sa
  2. Create the service account:

    $ oc create sa cluster-capacity-sa -n default
  3. Add the role to the service account:

    $ oc adm policy add-cluster-role-to-user cluster-capacity-role \
        system:serviceaccount:<namespace>:cluster-capacity-sa

    where:

    <namespace>
    Specifies the namespace where the pod is located.
  4. Define and create the pod spec:

    1. Create a YAML file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: small-pod
        labels:
          app: guestbook
          tier: frontend
      spec:
        containers:
        - name: php-redis
          image: gcr.io/google-samples/gb-frontend:v4
          imagePullPolicy: Always
          resources:
            limits:
              cpu: 150m
              memory: 100Mi
            requests:
              cpu: 150m
              memory: 100Mi
    2. Create the pod by running the following command:

      $ oc create -f <file_name>.yaml

      For example:

      $ oc create -f pod.yaml
  5. Created a config map object by running the following command:

    $ oc create configmap cluster-capacity-configmap \
        --from-file=pod.yaml=pod.yaml

    The cluster capacity analysis is mounted in a volume using a config map object named cluster-capacity-configmap to mount the input pod spec file pod.yaml into a volume test-volume at the path /test-pod.

  6. Create the job using the below example of a job specification file:

    1. Create a YAML file similar to the following:

      apiVersion: batch/v1
      kind: Job
      metadata:
        name: cluster-capacity-job
      spec:
        parallelism: 1
        completions: 1
        template:
          metadata:
            name: cluster-capacity-pod
          spec:
              containers:
              - name: cluster-capacity
                image: openshift/origin-cluster-capacity
                imagePullPolicy: "Always"
                volumeMounts:
                - mountPath: /test-pod
                  name: test-volume
                env:
                - name: CC_INCLUSTER 1
                  value: "true"
                command:
                - "/bin/sh"
                - "-ec"
                - |
                  /bin/cluster-capacity --podspec=/test-pod/pod.yaml --verbose
              restartPolicy: "Never"
              serviceAccountName: cluster-capacity-sa
              volumes:
              - name: test-volume
                configMap:
                  name: cluster-capacity-configmap
      1
      A required environment variable letting the cluster capacity tool know that it is running inside a cluster as a pod.
      The pod.yaml key of the ConfigMap object is the same as the Pod spec file name, though it is not required. By doing this, the input pod spec file can be accessed inside the pod as /test-pod/pod.yaml.
    2. Run the cluster capacity image as a job in a pod by running the following command:

      $ oc create -f cluster-capacity-job.yaml

Verification

  1. Check the job logs to find the number of pods that can be scheduled in the cluster:

    $ oc logs jobs/cluster-capacity-job

    Example output

    small-pod pod requirements:
            - CPU: 150m
            - Memory: 100Mi
    
    The cluster can schedule 52 instance(s) of the pod small-pod.
    
    Termination reason: Unschedulable: No nodes are available that match all of the
    following predicates:: Insufficient cpu (2).
    
    Pod distribution among nodes:
    small-pod
            - 192.168.124.214: 26 instance(s)
            - 192.168.124.120: 26 instance(s)

8.3. Restrict resource consumption with limit ranges

By default, containers run with unbounded compute resources on an OpenShift Container Platform cluster. With limit ranges, you can restrict resource consumption for specific objects in a project:

  • pods and containers: You can set minimum and maximum requirements for CPU and memory for pods and their containers.
  • Image streams: You can set limits on the number of images and tags in an ImageStream object.
  • Images: You can limit the size of images that can be pushed to an internal registry.
  • Persistent volume claims (PVC): You can restrict the size of the PVCs that can be requested.

If a pod does not meet the constraints imposed by the limit range, the pod cannot be created in the namespace.

8.3.1. About limit ranges

A limit range, defined by a LimitRange object, restricts resource consumption in a project. In the project you can set specific resource limits for a pod, container, image, image stream, or persistent volume claim (PVC).

All requests to create and modify resources are evaluated against each LimitRange object in the project. If the resource violates any of the enumerated constraints, the resource is rejected.

The following shows a limit range object for all components: pod, container, image, image stream, or PVC. You can configure limits for any or all of these components in the same object. You create a different limit range object for each project where you want to control resources.

Sample limit range object for a container

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits"
spec:
  limits:
    - type: "Container"
      max:
        cpu: "2"
        memory: "1Gi"
      min:
        cpu: "100m"
        memory: "4Mi"
      default:
        cpu: "300m"
        memory: "200Mi"
      defaultRequest:
        cpu: "200m"
        memory: "100Mi"
      maxLimitRequestRatio:
        cpu: "10"

8.3.1.1. About component limits

The following examples show limit range parameters for each component. The examples are broken out for clarity. You can create a single LimitRange object for any or all components as necessary.

8.3.1.1.1. Container limits

A limit range allows you to specify the minimum and maximum CPU and memory that each container in a pod can request for a specific project. If a container is created in the project, the container CPU and memory requests in the Pod spec must comply with the values set in the LimitRange object. If not, the pod does not get created.

  • The container CPU or memory request and limit must be greater than or equal to the min resource constraint for containers that are specified in the LimitRange object.
  • The container CPU or memory request and limit must be less than or equal to the max resource constraint for containers that are specified in the LimitRange object.

    If the LimitRange object defines a max CPU, you do not need to define a CPU request value in the Pod spec. But you must specify a CPU limit value that satisfies the maximum CPU constraint specified in the limit range.

  • The ratio of the container limits to requests must be less than or equal to the maxLimitRequestRatio value for containers that is specified in the LimitRange object.

    If the LimitRange object defines a maxLimitRequestRatio constraint, any new containers must have both a request and a limit value. OpenShift Container Platform calculates the limit-to-request ratio by dividing the limit by the request. This value should be a non-negative integer greater than 1.

    For example, if a container has cpu: 500 in the limit value, and cpu: 100 in the request value, the limit-to-request ratio for cpu is 5. This ratio must be less than or equal to the maxLimitRequestRatio.

If the Pod spec does not specify a container resource memory or limit, the default or defaultRequest CPU and memory values for containers specified in the limit range object are assigned to the container.

Container LimitRange object definition

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits" 1
spec:
  limits:
    - type: "Container"
      max:
        cpu: "2" 2
        memory: "1Gi" 3
      min:
        cpu: "100m" 4
        memory: "4Mi" 5
      default:
        cpu: "300m" 6
        memory: "200Mi" 7
      defaultRequest:
        cpu: "200m" 8
        memory: "100Mi" 9
      maxLimitRequestRatio:
        cpu: "10" 10

1
The name of the LimitRange object.
2
The maximum amount of CPU that a single container in a pod can request.
3
The maximum amount of memory that a single container in a pod can request.
4
The minimum amount of CPU that a single container in a pod can request.
5
The minimum amount of memory that a single container in a pod can request.
6
The default amount of CPU that a container can use if not specified in the Pod spec.
7
The default amount of memory that a container can use if not specified in the Pod spec.
8
The default amount of CPU that a container can request if not specified in the Pod spec.
9
The default amount of memory that a container can request if not specified in the Pod spec.
10
The maximum limit-to-request ratio for a container.
8.3.1.1.2. Pod limits

A limit range allows you to specify the minimum and maximum CPU and memory limits for all containers across a pod in a given project. To create a container in the project, the container CPU and memory requests in the Pod spec must comply with the values set in the LimitRange object. If not, the pod does not get created.

If the Pod spec does not specify a container resource memory or limit, the default or defaultRequest CPU and memory values for containers specified in the limit range object are assigned to the container.

Across all containers in a pod, the following must hold true:

  • The container CPU or memory request and limit must be greater than or equal to the min resource constraints for pods that are specified in the LimitRange object.
  • The container CPU or memory request and limit must be less than or equal to the max resource constraints for pods that are specified in the LimitRange object.
  • The ratio of the container limits to requests must be less than or equal to the maxLimitRequestRatio constraint specified in the LimitRange object.

Pod LimitRange object definition

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits" 1
spec:
  limits:
    - type: "Pod"
      max:
        cpu: "2" 2
        memory: "1Gi" 3
      min:
        cpu: "200m" 4
        memory: "6Mi" 5
      maxLimitRequestRatio:
        cpu: "10" 6

1
The name of the limit range object.
2
The maximum amount of CPU that a pod can request across all containers.
3
The maximum amount of memory that a pod can request across all containers.
4
The minimum amount of CPU that a pod can request across all containers.
5
The minimum amount of memory that a pod can request across all containers.
6
The maximum limit-to-request ratio for a container.
8.3.1.1.3. Image limits

A LimitRange object allows you to specify the maximum size of an image that can be pushed to an OpenShift image registry.

When pushing images to an OpenShift image registry, the following must hold true:

  • The size of the image must be less than or equal to the max size for images that is specified in the LimitRange object.

Image LimitRange object definition

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits" 1
spec:
  limits:
    - type: openshift.io/Image
      max:
        storage: 1Gi 2

1
The name of the LimitRange object.
2
The maximum size of an image that can be pushed to an OpenShift image registry.
Note

To prevent blobs that exceed the limit from being uploaded to the registry, the registry must be configured to enforce quotas.

Warning

The image size is not always available in the manifest of an uploaded image. This is especially the case for images built with Docker 1.10 or higher and pushed to a v2 registry. If such an image is pulled with an older Docker daemon, the image manifest is converted by the registry to schema v1 lacking all the size information. No storage limit set on images prevent it from being uploaded.

The issue is being addressed.

8.3.1.1.4. Image stream limits

A LimitRange object allows you to specify limits for image streams.

For each image stream, the following must hold true:

  • The number of image tags in an ImageStream specification must be less than or equal to the openshift.io/image-tags constraint in the LimitRange object.
  • The number of unique references to images in an ImageStream specification must be less than or equal to the openshift.io/images constraint in the limit range object.

Imagestream LimitRange object definition

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits" 1
spec:
  limits:
    - type: openshift.io/ImageStream
      max:
        openshift.io/image-tags: 20 2
        openshift.io/images: 30 3

1
The name of the LimitRange object.
2
The maximum number of unique image tags in the imagestream.spec.tags parameter in imagestream spec.
3
The maximum number of unique image references in the imagestream.status.tags parameter in the imagestream spec.

The openshift.io/image-tags resource represents unique image references. Possible references are an ImageStreamTag, an ImageStreamImage and a DockerImage. Tags can be created using the oc tag and oc import-image commands. No distinction is made between internal and external references. However, each unique reference tagged in an ImageStream specification is counted just once. It does not restrict pushes to an internal container image registry in any way, but is useful for tag restriction.

The openshift.io/images resource represents unique image names recorded in image stream status. It allows for restriction of a number of images that can be pushed to the OpenShift image registry. Internal and external references are not distinguished.

8.3.1.1.5. Persistent volume claim limits

A LimitRange object allows you to restrict the storage requested in a persistent volume claim (PVC).

Across all persistent volume claims in a project, the following must hold true:

  • The resource request in a persistent volume claim (PVC) must be greater than or equal the min constraint for PVCs that is specified in the LimitRange object.
  • The resource request in a persistent volume claim (PVC) must be less than or equal the max constraint for PVCs that is specified in the LimitRange object.

PVC LimitRange object definition

apiVersion: "v1"
kind: "LimitRange"
metadata:
  name: "resource-limits" 1
spec:
  limits:
    - type: "PersistentVolumeClaim"
      min:
        storage: "2Gi" 2
      max:
        storage: "50Gi" 3

1
The name of the LimitRange object.
2
The minimum amount of storage that can be requested in a persistent volume claim.
3
The maximum amount of storage that can be requested in a persistent volume claim.

8.3.2. Creating a Limit Range

To apply a limit range to a project:

  1. Create a LimitRange object with your required specifications:

    apiVersion: "v1"
    kind: "LimitRange"
    metadata:
      name: "resource-limits" 1
    spec:
      limits:
        - type: "Pod" 2
          max:
            cpu: "2"
            memory: "1Gi"
          min:
            cpu: "200m"
            memory: "6Mi"
        - type: "Container" 3
          max:
            cpu: "2"
            memory: "1Gi"
          min:
            cpu: "100m"
            memory: "4Mi"
          default: 4
            cpu: "300m"
            memory: "200Mi"
          defaultRequest: 5
            cpu: "200m"
            memory: "100Mi"
          maxLimitRequestRatio: 6
            cpu: "10"
        - type: openshift.io/Image 7
          max:
            storage: 1Gi
        - type: openshift.io/ImageStream 8
          max:
            openshift.io/image-tags: 20
            openshift.io/images: 30
        - type: "PersistentVolumeClaim" 9
          min:
            storage: "2Gi"
          max:
            storage: "50Gi"
    1
    Specify a name for the LimitRange object.
    2
    To set limits for a pod, specify the minimum and maximum CPU and memory requests as needed.
    3
    To set limits for a container, specify the minimum and maximum CPU and memory requests as needed.
    4
    Optional. For a container, specify the default amount of CPU or memory that a container can use, if not specified in the Pod spec.
    5
    Optional. For a container, specify the default amount of CPU or memory that a container can request, if not specified in the Pod spec.
    6
    Optional. For a container, specify the maximum limit-to-request ratio that can be specified in the Pod spec.
    7
    To set limits for an Image object, set the maximum size of an image that can be pushed to an OpenShift image registry.
    8
    To set limits for an image stream, set the maximum number of image tags and references that can be in the ImageStream object file, as needed.
    9
    To set limits for a persistent volume claim, set the minimum and maximum amount of storage that can be requested.
  2. Create the object:

    $ oc create -f <limit_range_file> -n <project> 1
    1
    Specify the name of the YAML file you created and the project where you want the limits to apply.

8.3.3. Viewing a limit

You can view any limits defined in a project by navigating in the web console to the project’s Quota page.

You can also use the CLI to view limit range details:

  1. Get the list of LimitRange object defined in the project. For example, for a project called demoproject:

    $ oc get limits -n demoproject
    NAME              CREATED AT
    resource-limits   2020-07-15T17:14:23Z
  2. Describe the LimitRange object you are interested in, for example the resource-limits limit range:

    $ oc describe limits resource-limits -n demoproject
    Name:                           resource-limits
    Namespace:                      demoproject
    Type                            Resource                Min     Max     Default Request Default Limit   Max Limit/Request Ratio
    ----                            --------                ---     ---     --------------- -------------   -----------------------
    Pod                             cpu                     200m    2       -               -               -
    Pod                             memory                  6Mi     1Gi     -               -               -
    Container                       cpu                     100m    2       200m            300m            10
    Container                       memory                  4Mi     1Gi     100Mi           200Mi           -
    openshift.io/Image              storage                 -       1Gi     -               -               -
    openshift.io/ImageStream        openshift.io/image      -       12      -               -               -
    openshift.io/ImageStream        openshift.io/image-tags -       10      -               -               -
    PersistentVolumeClaim           storage                 -       50Gi    -               -               -

8.3.4. Deleting a Limit Range

To remove any active LimitRange object to no longer enforce the limits in a project:

  • Run the following command:

    $ oc delete limits <limit_name>

8.4. Configuring cluster memory to meet container memory and risk requirements

As a cluster administrator, you can help your clusters operate efficiently through managing application memory by:

  • Determining the memory and risk requirements of a containerized application component and configuring the container memory parameters to suit those requirements.
  • Configuring containerized application runtimes (for example, OpenJDK) to adhere optimally to the configured container memory parameters.
  • Diagnosing and resolving memory-related error conditions associated with running in a container.

8.4.1. Understanding managing application memory

It is recommended to fully read the overview of how OpenShift Container Platform manages Compute Resources before proceeding.

For each kind of resource (memory, CPU, storage), OpenShift Container Platform allows optional request and limit values to be placed on each container in a pod.

Note the following about memory requests and memory limits:

  • Memory request

    • The memory request value, if specified, influences the OpenShift Container Platform scheduler. The scheduler considers the memory request when scheduling a container to a node, then fences off the requested memory on the chosen node for the use of the container.
    • If a node’s memory is exhausted, OpenShift Container Platform prioritizes evicting its containers whose memory usage most exceeds their memory request. In serious cases of memory exhaustion, the node OOM killer may select and kill a process in a container based on a similar metric.
    • The cluster administrator can assign quota or assign default values for the memory request value.
    • The cluster administrator can override the memory request values that a developer specifies, to manage cluster overcommit.
  • Memory limit

    • The memory limit value, if specified, provides a hard limit on the memory that can be allocated across all the processes in a container.
    • If the memory allocated by all of the processes in a container exceeds the memory limit, the node Out of Memory (OOM) killer will immediately select and kill a process in the container.
    • If both memory request and limit are specified, the memory limit value must be greater than or equal to the memory request.
    • The cluster administrator can assign quota or assign default values for the memory limit value.
    • The minimum memory limit is 12 MB. If a container fails to start due to a Cannot allocate memory pod event, the memory limit is too low. Either increase or remove the memory limit. Removing the limit allows pods to consume unbounded node resources.
8.4.1.1. Managing application memory strategy

The steps for sizing application memory on OpenShift Container Platform are as follows:

  1. Determine expected container memory usage

    Determine expected mean and peak container memory usage, empirically if necessary (for example, by separate load testing). Remember to consider all the processes that may potentially run in parallel in the container: for example, does the main application spawn any ancillary scripts?

  2. Determine risk appetite

    Determine risk appetite for eviction. If the risk appetite is low, the container should request memory according to the expected peak usage plus a percentage safety margin. If the risk appetite is higher, it may be more appropriate to request memory according to the expected mean usage.

  3. Set container memory request

    Set container memory request based on the above. The more accurately the request represents the application memory usage, the better. If the request is too high, cluster and quota usage will be inefficient. If the request is too low, the chances of application eviction increase.

  4. Set container memory limit, if required

    Set container memory limit, if required. Setting a limit has the effect of immediately killing a container process if the combined memory usage of all processes in the container exceeds the limit, and is therefore a mixed blessing. On the one hand, it may make unanticipated excess memory usage obvious early ("fail fast"); on the other hand it also terminates processes abruptly.

    Note that some OpenShift Container Platform clusters may require a limit value to be set; some may override the request based on the limit; and some application images rely on a limit value being set as this is easier to detect than a request value.

    If the memory limit is set, it should not be set to less than the expected peak container memory usage plus a percentage safety margin.

  5. Ensure application is tuned

    Ensure application is tuned with respect to configured request and limit values, if appropriate. This step is particularly relevant to applications which pool memory, such as the JVM. The rest of this page discusses this.

8.4.2. Understanding OpenJDK settings for OpenShift Container Platform

The default OpenJDK settings do not work well with containerized environments. As a result, some additional Java memory settings must always be provided whenever running the OpenJDK in a container.

The JVM memory layout is complex, version dependent, and describing it in detail is beyond the scope of this documentation. However, as a starting point for running OpenJDK in a container, at least the following three memory-related tasks are key:

  1. Overriding the JVM maximum heap size.
  2. Encouraging the JVM to release unused memory to the operating system, if appropriate.
  3. Ensuring all JVM processes within a container are appropriately configured.

Optimally tuning JVM workloads for running in a container is beyond the scope of this documentation, and may involve setting multiple additional JVM options.

8.4.2.1. Understanding how to override the JVM maximum heap size

For many Java workloads, the JVM heap is the largest single consumer of memory. Currently, the OpenJDK defaults to allowing up to 1/4 (1/-XX:MaxRAMFraction) of the compute node’s memory to be used for the heap, regardless of whether the OpenJDK is running in a container or not. It is therefore essential to override this behavior, especially if a container memory limit is also set.

There are at least two ways the above can be achieved:

  • If the container memory limit is set and the experimental options are supported by the JVM, set -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap.

    Note

    The UseCGroupMemoryLimitForHeap option has been removed in JDK 11. Use -XX:+UseContainerSupport instead.

    This sets -XX:MaxRAM to the container memory limit, and the maximum heap size (-XX:MaxHeapSize / -Xmx) to 1/-XX:MaxRAMFraction (1/4 by default).

  • Directly override one of -XX:MaxRAM, -XX:MaxHeapSize or -Xmx.

    This option involves hard-coding a value, but has the advantage of allowing a safety margin to be calculated.

8.4.2.2. Understanding how to encourage the JVM to release unused memory to the operating system

By default, the OpenJDK does not aggressively return unused memory to the operating system. This may be appropriate for many containerized Java workloads, but notable exceptions include workloads where additional active processes co-exist with a JVM within a container, whether those additional processes are native, additional JVMs, or a combination of the two.

Java-based agents can use the following JVM arguments to encourage the JVM to release unused memory to the operating system:

-XX:+UseParallelGC
-XX:MinHeapFreeRatio=5 -XX:MaxHeapFreeRatio=10 -XX:GCTimeRatio=4
-XX:AdaptiveSizePolicyWeight=90.

These arguments are intended to return heap memory to the operating system whenever allocated memory exceeds 110% of in-use memory (-XX:MaxHeapFreeRatio), spending up to 20% of CPU time in the garbage collector (-XX:GCTimeRatio). At no time will the application heap allocation be less than the initial heap allocation (overridden by -XX:InitialHeapSize / -Xms). Detailed additional information is available Tuning Java’s footprint in OpenShift (Part 1), Tuning Java’s footprint in OpenShift (Part 2), and at OpenJDK and Containers.

8.4.2.3. Understanding how to ensure all JVM processes within a container are appropriately configured

In the case that multiple JVMs run in the same container, it is essential to ensure that they are all configured appropriately. For many workloads it will be necessary to grant each JVM a percentage memory budget, leaving a perhaps substantial additional safety margin.

Many Java tools use different environment variables (JAVA_OPTS, GRADLE_OPTS, and so on) to configure their JVMs and it can be challenging to ensure that the right settings are being passed to the right JVM.

The JAVA_TOOL_OPTIONS environment variable is always respected by the OpenJDK, and values specified in JAVA_TOOL_OPTIONS will be overridden by other options specified on the JVM command line. By default, to ensure that these options are used by default for all JVM workloads run in the Java-based agent image, the OpenShift Container Platform Jenkins Maven agent image sets:

JAVA_TOOL_OPTIONS="-XX:+UnlockExperimentalVMOptions
-XX:+UseCGroupMemoryLimitForHeap -Dsun.zip.disableMemoryMapping=true"
Note

The UseCGroupMemoryLimitForHeap option has been removed in JDK 11. Use -XX:+UseContainerSupport instead.

This does not guarantee that additional options are not required, but is intended to be a helpful starting point.

8.4.3. Finding the memory request and limit from within a pod

An application wishing to dynamically discover its memory request and limit from within a pod should use the Downward API.

Procedure

  1. Configure the pod to add the MEMORY_REQUEST and MEMORY_LIMIT stanzas:

    1. Create a YAML file similar to the following:

      apiVersion: v1
      kind: Pod
      metadata:
        name: test
      spec:
        containers:
        - name: test
          image: fedora:latest
          command:
          - sleep
          - "3600"
          env:
          - name: MEMORY_REQUEST 1
            valueFrom:
              resourceFieldRef:
                containerName: test
                resource: requests.memory
          - name: MEMORY_LIMIT 2
            valueFrom:
              resourceFieldRef:
                containerName: test
                resource: limits.memory
          resources:
            requests:
              memory: 384Mi
            limits:
              memory: 512Mi
      1
      Add this stanza to discover the application memory request value.
      2
      Add this stanza to discover the application memory limit value.
    2. Create the pod by running the following command:

      $ oc create -f <file-name>.yaml

Verification

  1. Access the pod using a remote shell:

    $ oc rsh test
  2. Check that the requested values were applied:

    $ env | grep MEMORY | sort

    Example output

    MEMORY_LIMIT=536870912
    MEMORY_REQUEST=402653184

Note

The memory limit value can also be read from inside the container by the /sys/fs/cgroup/memory/memory.limit_in_bytes file.

8.4.4. Understanding OOM kill policy

OpenShift Container Platform can kill a process in a container if the total memory usage of all the processes in the container exceeds the memory limit, or in serious cases of node memory exhaustion.

When a process is Out of Memory (OOM) killed, this might result in the container exiting immediately. If the container PID 1 process receives the SIGKILL, the container will exit immediately. Otherwise, the container behavior is dependent on the behavior of the other processes.

For example, a container process exited with code 137, indicating it received a SIGKILL signal.

If the container does not exit immediately, an OOM kill is detectable as follows:

  1. Access the pod using a remote shell:

    # oc rsh test
  2. Run the following command to see the current OOM kill count in /sys/fs/cgroup/memory/memory.oom_control:

    $ grep '^oom_kill ' /sys/fs/cgroup/memory/memory.oom_control

    Example output

    oom_kill 0

  3. Run the following command to provoke an OOM kill:

    $ sed -e '' </dev/zero

    Example output

    Killed

  4. Run the following command to view the exit status of the sed command:

    $ echo $?

    Example output

    137

    The 137 code indicates the container process exited with code 137, indicating it received a SIGKILL signal.

  5. Run the following command to see that the OOM kill counter in /sys/fs/cgroup/memory/memory.oom_control incremented:

    $ grep '^oom_kill ' /sys/fs/cgroup/memory/memory.oom_control

    Example output

    oom_kill 1

    If one or more processes in a pod are OOM killed, when the pod subsequently exits, whether immediately or not, it will have phase Failed and reason OOMKilled. An OOM-killed pod might be restarted depending on the value of restartPolicy. If not restarted, controllers such as the replication controller will notice the pod’s failed status and create a new pod to replace the old one.

    Use the follwing command to get the pod status:

    $ oc get pod test

    Example output

    NAME      READY     STATUS      RESTARTS   AGE
    test      0/1       OOMKilled   0          1m

    • If the pod has not restarted, run the following command to view the pod:

      $ oc get pod test -o yaml

      Example output

      ...
      status:
        containerStatuses:
        - name: test
          ready: false
          restartCount: 0
          state:
            terminated:
              exitCode: 137
              reason: OOMKilled
        phase: Failed

    • If restarted, run the following command to view the pod:

      $ oc get pod test -o yaml

      Example output

      ...
      status:
        containerStatuses:
        - name: test
          ready: true
          restartCount: 1
          lastState:
            terminated:
              exitCode: 137
              reason: OOMKilled
          state:
            running:
        phase: Running

8.4.5. Understanding pod eviction

OpenShift Container Platform may evict a pod from its node when the node’s memory is exhausted. Depending on the extent of memory exhaustion, the eviction may or may not be graceful. Graceful eviction implies the main process (PID 1) of each container receiving a SIGTERM signal, then some time later a SIGKILL signal if the process has not exited already. Non-graceful eviction implies the main process of each container immediately receiving a SIGKILL signal.

An evicted pod has phase Failed and reason Evicted. It will not be restarted, regardless of the value of restartPolicy. However, controllers such as the replication controller will notice the pod’s failed status and create a new pod to replace the old one.

$ oc get pod test

Example output

NAME      READY     STATUS    RESTARTS   AGE
test      0/1       Evicted   0          1m

$ oc get pod test -o yaml

Example output

...
status:
  message: 'Pod The node was low on resource: [MemoryPressure].'
  phase: Failed
  reason: Evicted

8.5. Configuring your cluster to place pods on overcommitted nodes

In an overcommitted state, the sum of the container compute resource requests and limits exceeds the resources available on the system. For example, you might want to use overcommitment in development environments where a trade-off of guaranteed performance for capacity is acceptable.

Containers can specify compute resource requests and limits. Requests are used for scheduling your container and provide a minimum service guarantee. Limits constrain the amount of compute resource that can be consumed on your node.

The scheduler attempts to optimize the compute resource use across all nodes in your cluster. It places pods onto specific nodes, taking the pods' compute resource requests and nodes' available capacity into consideration.

OpenShift Container Platform administrators can control the level of overcommit and manage container density on nodes. You can configure cluster-level overcommit using the ClusterResourceOverride Operator to override the ratio between requests and limits set on developer containers. In conjunction with node overcommit and project memory and CPU limits and defaults, you can adjust the resource limit and request to achieve the desired level of overcommit.

Note

In OpenShift Container Platform, you must enable cluster-level overcommit. Node overcommitment is enabled by default. See Disabling overcommitment for a node.

8.5.1. Resource requests and overcommitment

For each compute resource, a container may specify a resource request and limit. Scheduling decisions are made based on the request to ensure that a node has enough capacity available to meet the requested value. If a container specifies limits, but omits requests, the requests are defaulted to the limits. A container is not able to exceed the specified limit on the node.

The enforcement of limits is dependent upon the compute resource type. If a container makes no request or limit, the container is scheduled to a node with no resource guarantees. In practice, the container is able to consume as much of the specified resource as is available with the lowest local priority. In low resource situations, containers that specify no resource requests are given the lowest quality of service.

Scheduling is based on resources requested, while quota and hard limits refer to resource limits, which can be set higher than requested resources. The difference between request and limit determines the level of overcommit; for instance, if a container is given a memory request of 1Gi and a memory limit of 2Gi, it is scheduled based on the 1Gi request being available on the node, but could use up to 2Gi; so it is 200% overcommitted.

8.5.2. Cluster-level overcommit using the Cluster Resource Override Operator

The Cluster Resource Override Operator is an admission webhook that allows you to control the level of overcommit and manage container density across all the nodes in your cluster. The Operator controls how nodes in specific projects can exceed defined memory and CPU limits.

You must install the Cluster Resource Override Operator using the OpenShift Container Platform console or CLI as shown in the following sections. During the installation, you create a ClusterResourceOverride custom resource (CR), where you set the level of overcommit, as shown in the following example:

apiVersion: operator.autoscaling.openshift.io/v1
kind: ClusterResourceOverride
metadata:
    name: cluster 1
spec:
  podResourceOverride:
    spec:
      memoryRequestToLimitPercent: 50 2
      cpuRequestToLimitPercent: 25 3
      limitCPUToMemoryPercent: 200 4
# ...
1
The name must be cluster.
2
Optional. If a container memory limit has been specified or defaulted, the memory request is overridden to this percentage of the limit, between 1-100. The default is 50.
3
Optional. If a container CPU limit has been specified or defaulted, the CPU request is overridden to this percentage of the limit, between 1-100. The default is 25.
4
Optional. If a container memory limit has been specified or defaulted, the CPU limit is overridden to a percentage of the memory limit, if specified. Scaling 1Gi of RAM at 100 percent is equal to 1 CPU core. This is processed prior to overriding the CPU request (if configured). The default is 200.
Note

The Cluster Resource Override Operator overrides have no effect if limits have not been set on containers. Create a LimitRange object with default limits per individual project or configure limits in Pod specs for the overrides to apply.

When configured, overrides can be enabled per-project by applying the following label to the Namespace object for each project:

apiVersion: v1
kind: Namespace
metadata:

# ...

  labels:
    clusterresourceoverrides.admission.autoscaling.openshift.io/enabled: "true"

# ...

The Operator watches for the ClusterResourceOverride CR and ensures that the ClusterResourceOverride admission webhook is installed into the same namespace as the operator.

8.5.2.1. Installing the Cluster Resource Override Operator using the web console

You can use the OpenShift Container Platform web console to install the Cluster Resource Override Operator to help control overcommit in your cluster.

Prerequisites

  • The Cluster Resource Override Operator has no effect if limits have not been set on containers. You must specify default limits for a project using a LimitRange object or configure limits in Pod specs for the overrides to apply.

Procedure

To install the Cluster Resource Override Operator using the OpenShift Container Platform web console:

  1. In the OpenShift Container Platform web console, navigate to HomeProjects

    1. Click Create Project.
    2. Specify clusterresourceoverride-operator as the name of the project.
    3. Click Create.
  2. Navigate to OperatorsOperatorHub.

    1. Choose ClusterResourceOverride Operator from the list of available Operators and click Install.
    2. On the Install Operator page, make sure A specific Namespace on the cluster is selected for Installation Mode.
    3. Make sure clusterresourceoverride-operator is selected for Installed Namespace.
    4. Select an Update Channel and Approval Strategy.
    5. Click Install.
  3. On the Installed Operators page, click ClusterResourceOverride.

    1. On the ClusterResourceOverride Operator details page, click Create ClusterResourceOverride.
    2. On the Create ClusterResourceOverride page, click YAML view and edit the YAML template to set the overcommit values as needed:

      apiVersion: operator.autoscaling.openshift.io/v1
      kind: ClusterResourceOverride
      metadata:
        name: cluster 1
      spec:
        podResourceOverride:
          spec:
            memoryRequestToLimitPercent: 50 2
            cpuRequestToLimitPercent: 25 3
            limitCPUToMemoryPercent: 200 4
      # ...
      1
      The name must be cluster.
      2
      Optional. Specify the percentage to override the container memory limit, if used, between 1-100. The default is 50.
      3
      Optional. Specify the percentage to override the container CPU limit, if used, between 1-100. The default is 25.
      4
      Optional. Specify the percentage to override the container memory limit, if used. Scaling 1Gi of RAM at 100 percent is equal to 1 CPU core. This is processed prior to overriding the CPU request, if configured. The default is 200.
    3. Click Create.
  4. Check the current state of the admission webhook by checking the status of the cluster custom resource:

    1. On the ClusterResourceOverride Operator page, click cluster.
    2. On the ClusterResourceOverride Details page, click YAML. The mutatingWebhookConfigurationRef section appears when the webhook is called.

      apiVersion: operator.autoscaling.openshift.io/v1
      kind: ClusterResourceOverride
      metadata:
        annotations:
          kubectl.kubernetes.io/last-applied-configuration: |
            {"apiVersion":"operator.autoscaling.openshift.io/v1","kind":"ClusterResourceOverride","metadata":{"annotations":{},"name":"cluster"},"spec":{"podResourceOverride":{"spec":{"cpuRequestToLimitPercent":25,"limitCPUToMemoryPercent":200,"memoryRequestToLimitPercent":50}}}}
        creationTimestamp: "2019-12-18T22:35:02Z"
        generation: 1
        name: cluster
        resourceVersion: "127622"
        selfLink: /apis/operator.autoscaling.openshift.io/v1/clusterresourceoverrides/cluster
        uid: 978fc959-1717-4bd1-97d0-ae00ee111e8d
      spec:
        podResourceOverride:
          spec:
            cpuRequestToLimitPercent: 25
            limitCPUToMemoryPercent: 200
            memoryRequestToLimitPercent: 50
      status:
      
      # ...
      
          mutatingWebhookConfigurationRef: 1
            apiVersion: admissionregistration.k8s.io/v1
            kind: MutatingWebhookConfiguration
            name: clusterresourceoverrides.admission.autoscaling.openshift.io
            resourceVersion: "127621"
            uid: 98b3b8ae-d5ce-462b-8ab5-a729ea8f38f3
      
      # ...
      1
      Reference to the ClusterResourceOverride admission webhook.
8.5.2.2. Installing the Cluster Resource Override Operator using the CLI

You can use the OpenShift Container Platform CLI to install the Cluster Resource Override Operator to help control overcommit in your cluster.

Prerequisites

  • The Cluster Resource Override Operator has no effect if limits have not been set on containers. You must specify default limits for a project using a LimitRange object or configure limits in Pod specs for the overrides to apply.

Procedure

To install the Cluster Resource Override Operator using the CLI:

  1. Create a namespace for the Cluster Resource Override Operator:

    1. Create a Namespace object YAML file (for example, cro-namespace.yaml) for the Cluster Resource Override Operator:

      apiVersion: v1
      kind: Namespace
      metadata:
        name: clusterresourceoverride-operator
    2. Create the namespace:

      $ oc create -f <file-name>.yaml

      For example:

      $ oc create -f cro-namespace.yaml
  2. Create an Operator group:

    1. Create an OperatorGroup object YAML file (for example, cro-og.yaml) for the Cluster Resource Override Operator:

      apiVersion: operators.coreos.com/v1
      kind: OperatorGroup
      metadata:
        name: clusterresourceoverride-operator
        namespace: clusterresourceoverride-operator
      spec:
        targetNamespaces:
          - clusterresourceoverride-operator
    2. Create the Operator Group:

      $ oc create -f <file-name>.yaml

      For example:

      $ oc create -f cro-og.yaml
  3. Create a subscription:

    1. Create a Subscription object YAML file (for example, cro-sub.yaml) for the Cluster Resource Override Operator:

      apiVersion: operators.coreos.com/v1alpha1
      kind: Subscription
      metadata:
        name: clusterresourceoverride
        namespace: clusterresourceoverride-operator
      spec:
        channel: "4.12"
        name: clusterresourceoverride
        source: redhat-operators
        sourceNamespace: openshift-marketplace
    2. Create the subscription:

      $ oc create -f <file-name>.yaml

      For example:

      $ oc create -f cro-sub.yaml
  4. Create a ClusterResourceOverride custom resource (CR) object in the clusterresourceoverride-operator namespace:

    1. Change to the clusterresourceoverride-operator namespace.

      $ oc project clusterresourceoverride-operator
    2. Create a ClusterResourceOverride object YAML file (for example, cro-cr.yaml) for the Cluster Resource Override Operator:

      apiVersion: operator.autoscaling.openshift.io/v1
      kind: ClusterResourceOverride
      metadata:
          name: cluster 1
      spec:
        podResourceOverride:
          spec:
            memoryRequestToLimitPercent: 50 2
            cpuRequestToLimitPercent: 25 3
            limitCPUToMemoryPercent: 200 4
      1
      The name must be cluster.
      2
      Optional. Specify the percentage to override the container memory limit, if used, between 1-100. The default is 50.
      3
      Optional. Specify the percentage to override the container CPU limit, if used, between 1-100. The default is 25.
      4
      Optional. Specify the percentage to override the container memory limit, if used. Scaling 1Gi of RAM at 100 percent is equal to 1 CPU core. This is processed prior to overriding the CPU request, if configured. The default is 200.
    3. Create the ClusterResourceOverride object:

      $ oc create -f <file-name>.yaml

      For example:

      $ oc create -f cro-cr.yaml
  5. Verify the current state of the admission webhook by checking the status of the cluster custom resource.

    $ oc get clusterresourceoverride cluster -n clusterresourceoverride-operator -o yaml

    The mutatingWebhookConfigurationRef section appears when the webhook is called.

    Example output

    apiVersion: operator.autoscaling.openshift.io/v1
    kind: ClusterResourceOverride
    metadata:
      annotations:
        kubectl.kubernetes.io/last-applied-configuration: |
          {"apiVersion":"operator.autoscaling.openshift.io/v1","kind":"ClusterResourceOverride","metadata":{"annotations":{},"name":"cluster"},"spec":{"podResourceOverride":{"spec":{"cpuRequestToLimitPercent":25,"limitCPUToMemoryPercent":200,"memoryRequestToLimitPercent":50}}}}
      creationTimestamp: "2019-12-18T22:35:02Z"
      generation: 1
      name: cluster
      resourceVersion: "127622"
      selfLink: /apis/operator.autoscaling.openshift.io/v1/clusterresourceoverrides/cluster
      uid: 978fc959-1717-4bd1-97d0-ae00ee111e8d
    spec:
      podResourceOverride:
        spec:
          cpuRequestToLimitPercent: 25
          limitCPUToMemoryPercent: 200
          memoryRequestToLimitPercent: 50
    status:
    
    # ...
    
        mutatingWebhookConfigurationRef: 1
          apiVersion: admissionregistration.k8s.io/v1
          kind: MutatingWebhookConfiguration
          name: clusterresourceoverrides.admission.autoscaling.openshift.io
          resourceVersion: "127621"
          uid: 98b3b8ae-d5ce-462b-8ab5-a729ea8f38f3
    
    # ...

    1
    Reference to the ClusterResourceOverride admission webhook.
8.5.2.3. Configuring cluster-level overcommit

The Cluster Resource Override Operator requires a ClusterResourceOverride custom resource (CR) and a label for each project where you want the Operator to control overcommit.

Prerequisites

  • The Cluster Resource Override Operator has no effect if limits have not been set on containers. You must specify default limits for a project using a LimitRange object or configure limits in Pod specs for the overrides to apply.

Procedure

To modify cluster-level overcommit:

  1. Edit the ClusterResourceOverride CR:

    apiVersion: operator.autoscaling.openshift.io/v1
    kind: ClusterResourceOverride
    metadata:
        name: cluster
    spec:
      podResourceOverride:
        spec:
          memoryRequestToLimitPercent: 50 1
          cpuRequestToLimitPercent: 25 2
          limitCPUToMemoryPercent: 200 3
    # ...
    1
    Optional. Specify the percentage to override the container memory limit, if used, between 1-100. The default is 50.
    2
    Optional. Specify the percentage to override the container CPU limit, if used, between 1-100. The default is 25.
    3
    Optional. Specify the percentage to override the container memory limit, if used. Scaling 1Gi of RAM at 100 percent is equal to 1 CPU core. This is processed prior to overriding the CPU request, if configured. The default is 200.
  2. Ensure the following label has been added to the Namespace object for each project where you want the Cluster Resource Override Operator to control overcommit:

    apiVersion: v1
    kind: Namespace
    metadata:
    
    # ...
    
      labels:
        clusterresourceoverrides.admission.autoscaling.openshift.io/enabled: "true" 1
    
    # ...
    1
    Add this label to each project.

8.5.3. Node-level overcommit

You can use various ways to control overcommit on specific nodes, such as quality of service (QOS) guarantees, CPU limits, or reserve resources. You can also disable overcommit for specific nodes and specific projects.

8.5.3.1. Understanding compute resources and containers

The node-enforced behavior for compute resources is specific to the resource type.

8.5.3.1.1. Understanding container CPU requests

A container is guaranteed the amount of CPU it requests and is additionally able to consume excess CPU available on the node, up to any limit specified by the container. If multiple containers are attempting to use excess CPU, CPU time is distributed based on the amount of CPU requested by each container.

For example, if one container requested 500m of CPU time and another container requested 250m of CPU time, then any extra CPU time available on the node is distributed among the containers in a 2:1 ratio. If a container specified a limit, it will be throttled not to use more CPU than the specified limit. CPU requests are enforced using the CFS shares support in the Linux kernel. By default, CPU limits are enforced using the CFS quota support in the Linux kernel over a 100ms measuring interval, though this can be disabled.

8.5.3.1.2. Understanding container memory requests

A container is guaranteed the amount of memory it requests. A container can use more memory than requested, but once it exceeds its requested amount, it could be terminated in a low memory situation on the node. If a container uses less memory than requested, it will not be terminated unless system tasks or daemons need more memory than was accounted for in the node’s resource reservation. If a container specifies a limit on memory, it is immediately terminated if it exceeds the limit amount.

8.5.3.2. Understanding overcommitment and quality of service classes

A node is overcommitted when it has a pod scheduled that makes no request, or when the sum of limits across all pods on that node exceeds available machine capacity.

In an overcommitted environment, it is possible that the pods on the node will attempt to use more compute resource than is available at any given point in time. When this occurs, the node must give priority to one pod over another. The facility used to make this decision is referred to as a Quality of Service (QoS) Class.

A pod is designated as one of three QoS classes with decreasing order of priority:

Table 8.19. Quality of Service Classes
PriorityClass NameDescription

1 (highest)

Guaranteed

If limits and optionally requests are set (not equal to 0) for all resources and they are equal, then the pod is classified as Guaranteed.

2

Burstable

If requests and optionally limits are set (not equal to 0) for all resources, and they are not equal, then the pod is classified as Burstable.

3 (lowest)

BestEffort

If requests and limits are not set for any of the resources, then the pod is classified as BestEffort.

Memory is an incompressible resource, so in low memory situations, containers that have the lowest priority are terminated first:

  • Guaranteed containers are considered top priority, and are guaranteed to only be terminated if they exceed their limits, or if the system is under memory pressure and there are no lower priority containers that can be evicted.
  • Burstable containers under system memory pressure are more likely to be terminated once they exceed their requests and no other BestEffort containers exist.
  • BestEffort containers are treated with the lowest priority. Processes in these containers are first to be terminated if the system runs out of memory.
8.5.3.2.1. Understanding how to reserve memory across quality of service tiers

You can use the qos-reserved parameter to specify a percentage of memory to be reserved by a pod in a particular QoS level. This feature attempts to reserve requested resources to exclude pods from lower OoS classes from using resources requested by pods in higher QoS classes.

OpenShift Container Platform uses the qos-reserved parameter as follows:

  • A value of qos-reserved=memory=100% will prevent the Burstable and BestEffort QoS classes from consuming memory that was requested by a higher QoS class. This increases the risk of inducing OOM on BestEffort and Burstable workloads in favor of increasing memory resource guarantees for Guaranteed and Burstable workloads.
  • A value of qos-reserved=memory=50% will allow the Burstable and BestEffort QoS classes to consume half of the memory requested by a higher QoS class.
  • A value of qos-reserved=memory=0% will allow a Burstable and BestEffort QoS classes to consume up to the full node allocatable amount if available, but increases the risk that a Guaranteed workload will not have access to requested memory. This condition effectively disables this feature.
8.5.3.3. Understanding swap memory and QOS

You can disable swap by default on your nodes to preserve quality of service (QOS) guarantees. Otherwise, physical resources on a node can oversubscribe, affecting the resource guarantees the Kubernetes scheduler makes during pod placement.

For example, if two guaranteed pods have reached their memory limit, each container could start using swap memory. Eventually, if there is not enough swap space, processes in the pods can be terminated due to the system being oversubscribed.

Failing to disable swap results in nodes not recognizing that they are experiencing MemoryPressure, resulting in pods not receiving the memory they made in their scheduling request. As a result, additional pods are placed on the node to further increase memory pressure, ultimately increasing your risk of experiencing a system out of memory (OOM) event.

Important

If swap is enabled, any out-of-resource handling eviction thresholds for available memory will not work as expected. Take advantage of out-of-resource handling to allow pods to be evicted from a node when it is under memory pressure, and rescheduled on an alternative node that has no such pressure.

8.5.3.4. Understanding nodes overcommitment

In an overcommitted environment, it is important to properly configure your node to provide best system behavior.

When the node starts, it ensures that the kernel tunable flags for memory management are set properly. The kernel should never fail memory allocations unless it runs out of physical memory.

To ensure this behavior, OpenShift Container Platform configures the kernel to always overcommit memory by setting the vm.overcommit_memory parameter to 1, overriding the default operating system setting.

OpenShift Container Platform also configures the kernel not to panic when it runs out of memory by setting the vm.panic_on_oom parameter to 0. A setting of 0 instructs the kernel to call oom_killer in an Out of Memory (OOM) condition, which kills processes based on priority

You can view the current setting by running the following commands on your nodes:

$ sysctl -a |grep commit

Example output

#...
vm.overcommit_memory = 0
#...

$ sysctl -a |grep panic

Example output

#...
vm.panic_on_oom = 0
#...

Note

The above flags should already be set on nodes, and no further action is required.

You can also perform the following configurations for each node:

  • Disable or enforce CPU limits using CPU CFS quotas
  • Reserve resources for system processes
  • Reserve memory across quality of service tiers
8.5.3.5. Disabling or enforcing CPU limits using CPU CFS quotas

Nodes by default enforce specified CPU limits using the Completely Fair Scheduler (CFS) quota support in the Linux kernel.

If you disable CPU limit enforcement, it is important to understand the impact on your node:

  • If a container has a CPU request, the request continues to be enforced by CFS shares in the Linux kernel.
  • If a container does not have a CPU request, but does have a CPU limit, the CPU request defaults to the specified CPU limit, and is enforced by CFS shares in the Linux kernel.
  • If a container has both a CPU request and limit, the CPU request is enforced by CFS shares in the Linux kernel, and the CPU limit has no impact on the node.

Prerequisites

  • Obtain the label associated with the static MachineConfigPool CRD for the type of node you want to configure by entering the following command:

    $ oc edit machineconfigpool <name>

    For example:

    $ oc edit machineconfigpool worker

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfigPool
    metadata:
      creationTimestamp: "2022-11-16T15:34:25Z"
      generation: 4
      labels:
        pools.operator.machineconfiguration.openshift.io/worker: "" 1
      name: worker

    1
    The label appears under Labels.
    Tip

    If the label is not present, add a key/value pair such as:

    $ oc label machineconfigpool worker custom-kubelet=small-pods

Procedure

  1. Create a custom resource (CR) for your configuration change.

    Sample configuration for a disabling CPU limits

    apiVersion: machineconfiguration.openshift.io/v1
    kind: KubeletConfig
    metadata:
      name: disable-cpu-units 1
    spec:
      machineConfigPoolSelector:
        matchLabels:
          pools.operator.machineconfiguration.openshift.io/worker: "" 2
      kubeletConfig:
        cpuCfsQuota: false 3

    1
    Assign a name to CR.
    2
    Specify the label from the machine config pool.
    3
    Set the cpuCfsQuota parameter to false.
  2. Run the following command to create the CR:

    $ oc create -f <file_name>.yaml
8.5.3.6. Reserving resources for system processes

To provide more reliable scheduling and minimize node resource overcommitment, each node can reserve a portion of its resources for use by system daemons that are required to run on your node for your cluster to function. In particular, it is recommended that you reserve resources for incompressible resources such as memory.

Procedure

To explicitly reserve resources for non-pod processes, allocate node resources by specifying resources available for scheduling. For more details, see Allocating Resources for Nodes.

8.5.3.7. Disabling overcommitment for a node

When enabled, overcommitment can be disabled on each node.

Procedure

To disable overcommitment in a node run the following command on that node:

$ sysctl -w vm.overcommit_memory=0

8.5.4. Project-level limits

To help control overcommit, you can set per-project resource limit ranges, specifying memory and CPU limits and defaults for a project that overcommit cannot exceed.

For information on project-level resource limits, see Additional resources.

Alternatively, you can disable overcommitment for specific projects.

8.5.4.1. Disabling overcommitment for a project

When enabled, overcommitment can be disabled per-project. For example, you can allow infrastructure components to be configured independently of overcommitment.

Procedure

To disable overcommitment in a project:

  1. Edit the namespace object to add the following annotation:

    apiVersion: v1
    kind: Namespace
    metadata:
      annotations:
        quota.openshift.io/cluster-resource-override-enabled: "false" 1
    # ...
    1
    Setting this annotation to false disables overcommit for this namespace.

8.5.5. Additional resources

8.6. Enabling Linux control group version 2 (cgroup v2)

You can enable Linux control group version 2 (cgroup v2) in your cluster by editing the node.config object. Enabling cgroup v2 in OpenShift Container Platform disables all cgroups version 1 controllers and hierarchies in your cluster. cgroup v1 is enabled by default.

cgroup v2 is the current version of the Linux cgroup API. cgroup v2 offers several improvements over cgroup v1, including a unified hierarchy, safer sub-tree delegation, new features such as Pressure Stall Information, and enhanced resource management and isolation. However, cgroup v2 has different CPU, memory, and I/O management characteristics than cgroup v1. Therefore, some workloads might experience slight differences in memory or CPU usage on clusters that run cgroup v2.

Note
  • If you run third-party monitoring and security agents that depend on the cgroup file system, update the agents to a version that supports cgroup v2.
  • If you have configured cgroup v2 and run cAdvisor as a stand-alone daemon set for monitoring pods and containers, update cAdvisor to v0.43.0 or later.
  • If you deploy Java applications, use versions that fully support cgroup v2, such as the following packages:

    • OpenJDK / HotSpot: jdk8u372, 11.0.16, 15 and later
    • IBM Semeru Runtimes: jdk8u345-b01, 11.0.16.0, 17.0.4.0, 18.0.2.0 and later
    • IBM SDK Java Technology Edition Version (IBM Java): 8.0.7.15 and later
Important

OpenShift Container Platform cgroups version 2 support is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

8.6.1. Configuring Linux cgroup v2

You enable cgroup v2 by editing the node.config object.

Note

Currently, disabling CPU load balancing is not supported by cgroup v2. As a result, you might not get the desired behavior from performance profiles if you have cgroup v2 enabled. Enabling cgroup v2 is not recommended if you are using performance profiles.

Prerequisites

  • You have a running OpenShift Container Platform cluster that uses version 4.12 or later.
  • You are logged in to the cluster as a user with administrative privileges.
  • You have enabled the TechPreviewNoUpgrade feature set by using the feature gates.

Procedure

  1. Enable cgroup v2 on nodes:

    1. Edit the node.config object:

      $ oc edit nodes.config/cluster
    2. Add spec.cgroupMode: "v2":

      Example node.config object

      apiVersion: config.openshift.io/v1
      kind: Node
      metadata:
        annotations:
          include.release.openshift.io/ibm-cloud-managed: "true"
          include.release.openshift.io/self-managed-high-availability: "true"
          include.release.openshift.io/single-node-developer: "true"
          release.openshift.io/create-only: "true"
        creationTimestamp: "2022-07-08T16:02:51Z"
        generation: 1
        name: cluster
        ownerReferences:
        - apiVersion: config.openshift.io/v1
          kind: ClusterVersion
          name: version
          uid: 36282574-bf9f-409e-a6cd-3032939293eb
        resourceVersion: "1865"
        uid: 0c0f7a4c-4307-4187-b591-6155695ac85b
      spec:
        cgroupMode: "v2" 1
      ...

      1
      Enables cgroup v2.

Verification

  1. Check the machine configs to see that the new machine configs were added:

    $ oc get mc

    Example output

    NAME                                               GENERATEDBYCONTROLLER                      IGNITIONVERSION   AGE
    00-master                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    00-worker                                          52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-master-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-container-runtime                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    01-worker-kubelet                                  52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    97-master-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0              3m 1
    99-worker-generated-kubelet                        52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0              3m
    99-master-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-master-ssh                                                                                 3.2.0             40m
    99-worker-generated-registries                     52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    99-worker-ssh                                                                                 3.2.0             40m
    rendered-master-23e785de7587df95a4b517e0647e5ab7   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    rendered-worker-5d596d9293ca3ea80c896a1191735bb1   52dd3ba6a9a527fc3ab42afac8d12b693534c8c9   3.2.0             33m
    worker-enable-cgroups-v2                                                                      3.2.0             10s

    1
    New machine configs are created, as expected.
  2. Check that the new kernelArguments were added to the new machine configs:

    $ oc describe mc <name>

    Example output

    apiVersion: machineconfiguration.openshift.io/v1
    kind: MachineConfig
    metadata:
      labels:
        machineconfiguration.openshift.io/role: worker
      name: 05-worker-kernelarg-selinuxpermissive
    spec:
      kernelArguments:
      - systemd_unified_cgroup_hierarchy=1 1
      - cgroup_no_v1="all" 2
      - psi=1 3

    1
    Enables cgroup v2 in systemd.
    2
    Disables cgroups v1.
    3
    Enables the Linux Pressure Stall Information (PSI) feature.
  3. Check the nodes to see that scheduling on the nodes is disabled. This indicates that the change is being applied:

    $ oc get nodes

    Example output

    NAME                                       STATUS                     ROLES    AGE   VERSION
    ci-ln-fm1qnwt-72292-99kt6-master-0         Ready                      master   58m   v1.25.0
    ci-ln-fm1qnwt-72292-99kt6-master-1         Ready                      master   58m   v1.25.0
    ci-ln-fm1qnwt-72292-99kt6-master-2         Ready                      master   58m   v1.25.0
    ci-ln-fm1qnwt-72292-99kt6-worker-a-h5gt4   Ready,SchedulingDisabled   worker   48m   v1.25.0
    ci-ln-fm1qnwt-72292-99kt6-worker-b-7vtmd   Ready                      worker   48m   v1.25.0
    ci-ln-fm1qnwt-72292-99kt6-worker-c-rhzkv   Ready                      worker   48m   v1.25.0

  4. After a node returns to the Ready state, start a debug session for that node:

    $ oc debug node/<node_name>
  5. Set /host as the root directory within the debug shell:

    sh-4.4# chroot /host
  6. Check that the sys/fs/cgroup/cgroup2fs file is present on your nodes. This file is created by cgroup v2:

    $ stat -c %T -f /sys/fs/cgroup

    Example output

    cgroup2fs

8.7. Enabling features using feature gates

As an administrator, you can use feature gates to enable features that are not part of the default set of features.

8.7.1. Understanding feature gates

You can use the FeatureGate custom resource (CR) to enable specific feature sets in your cluster. A feature set is a collection of OpenShift Container Platform features that are not enabled by default.

You can activate the following feature set by using the FeatureGate CR:

  • TechPreviewNoUpgrade. This feature set is a subset of the current Technology Preview features. This feature set allows you to enable these Technology Preview features on test clusters, where you can fully test them, while leaving the features disabled on production clusters.

    Warning

    Enabling the TechPreviewNoUpgrade feature set on your cluster cannot be undone and prevents minor version updates. You should not enable this feature set on production clusters.

    The following Technology Preview features are enabled by this feature set:

    • CSI automatic migration. Enables automatic migration for supported in-tree volume plugins to their equivalent Container Storage Interface (CSI) drivers. Supported for:

      • Azure File (CSIMigrationAzureFile)
      • VMware vSphere (CSIMigrationvSphere)
    • Shared Resources CSI Driver and Build CSI Volumes in OpenShift Builds. Enables the Container Storage Interface (CSI). (CSIDriverSharedResource)
    • CSI volumes. Enables CSI volume support for the OpenShift Container Platform build system. (BuildCSIVolumes)
    • Swap memory on nodes. Enables swap memory use for OpenShift Container Platform workloads on a per-node basis. (NodeSwap)
    • cgroups v2. Enables cgroup v2, the next version of the Linux cgroup API. (CGroupsV2)
    • crun. Enables the crun container runtime. (Crun)
    • Insights Operator. Enables the Insights Operator, which gathers OpenShift Container Platform configuration data and sends it to Red Hat. (InsightsConfigAPI)
    • External cloud providers. Enables support for external cloud providers for clusters on vSphere, AWS, Azure, and GCP. Support for OpenStack is GA. (ExternalCloudProvider)
    • Pod topology spread constraints. Enables the matchLabelKeys parameter for pod topology constraints. The parameter is list of pod label keys to select the pods over which spreading will be calculated. (MatchLabelKeysInPodTopologySpread)
    • Pod security admission enforcement. Enables restricted enforcement for pod security admission. Instead of only logging a warning, pods are rejected if they violate pod security standards. (OpenShiftPodSecurityAdmission)

      Note

      Pod security admission restricted enforcement is only activated if you enable the TechPreviewNoUpgrade feature set after your OpenShift Container Platform cluster is installed. It is not activated if you enable the TechPreviewNoUpgrade feature set during cluster installation.

For more information about the features activated by the TechPreviewNoUpgrade feature gate, see the following topics:

8.7.2. Enabling feature sets at installation

You can enable feature sets for all nodes in the cluster by editing the install-config.yaml file before you deploy the cluster.

Prerequisites

  • You have an install-config.yaml file.

Procedure

  1. Use the featureSet parameter to specify the name of the feature set you want to enable, such as TechPreviewNoUpgrade:

    Warning

    Enabling the TechPreviewNoUpgrade feature set on your cluster cannot be undone and prevents minor version updates. You should not enable this feature set on production clusters.

    Sample install-config.yaml file with an enabled feature set

    compute:
    - hyperthreading: Enabled
      name: worker
      platform:
        aws:
          rootVolume:
            iops: 2000
            size: 500
            type: io1
          metadataService:
            authentication: Optional
          type: c5.4xlarge
          zones:
          - us-west-2c
      replicas: 3
    featureSet: TechPreviewNoUpgrade

  2. Save the file and reference it when using the installation program to deploy the cluster.

Verification

You can verify that the feature gates are enabled by looking at the kubelet.conf file on a node after the nodes return to the ready state.

  1. From the Administrator perspective in the web console, navigate to ComputeNodes.
  2. Select a node.
  3. In the Node details page, click Terminal.
  4. In the terminal window, change your root directory to /host:

    sh-4.2# chroot /host
  5. View the kubelet.conf file:

    sh-4.2# cat /etc/kubernetes/kubelet.conf

    Sample output

    # ...
    featureGates:
      InsightsOperatorPullingSCA: true,
      LegacyNodeRoleBehavior: false
    # ...

    The features that are listed as true are enabled on your cluster.

    Note

    The features listed vary depending upon the OpenShift Container Platform version.

8.7.3. Enabling feature sets using the web console

You can use the OpenShift Container Platform web console to enable feature sets for all of the nodes in a cluster by editing the FeatureGate custom resource (CR).

Procedure

To enable feature sets:

  1. In the OpenShift Container Platform web console, switch to the AdministrationCustom Resource Definitions page.
  2. On the Custom Resource Definitions page, click FeatureGate.
  3. On the Custom Resource Definition Details page, click the Instances tab.
  4. Click the cluster feature gate, then click the YAML tab.
  5. Edit the cluster instance to add specific feature sets:

    Warning

    Enabling the TechPreviewNoUpgrade feature set on your cluster cannot be undone and prevents minor version updates. You should not enable this feature set on production clusters.

    Sample Feature Gate custom resource

    apiVersion: config.openshift.io/v1
    kind: FeatureGate
    metadata:
      name: cluster 1
    # ...
    spec:
      featureSet: TechPreviewNoUpgrade 2

    1
    The name of the FeatureGate CR must be cluster.
    2
    Add the feature set that you want to enable:
    • TechPreviewNoUpgrade enables specific Technology Preview features.

    After you save the changes, new machine configs are created, the machine config pools are updated, and scheduling on each node is disabled while the change is being applied.

Verification

You can verify that the feature gates are enabled by looking at the kubelet.conf file on a node after the nodes return to the ready state.

  1. From the Administrator perspective in the web console, navigate to ComputeNodes.
  2. Select a node.
  3. In the Node details page, click Terminal.
  4. In the terminal window, change your root directory to /host:

    sh-4.2# chroot /host
  5. View the kubelet.conf file:

    sh-4.2# cat /etc/kubernetes/kubelet.conf

    Sample output

    # ...
    featureGates:
      InsightsOperatorPullingSCA: true,
      LegacyNodeRoleBehavior: false
    # ...

    The features that are listed as true are enabled on your cluster.

    Note

    The features listed vary depending upon the OpenShift Container Platform version.

8.7.4. Enabling feature sets using the CLI

You can use the OpenShift CLI (oc) to enable feature sets for all of the nodes in a cluster by editing the FeatureGate custom resource (CR).

Prerequisites

  • You have installed the OpenShift CLI (oc).

Procedure

To enable feature sets:

  1. Edit the FeatureGate CR named cluster:

    $ oc edit featuregate cluster
    Warning

    Enabling the TechPreviewNoUpgrade feature set on your cluster cannot be undone and prevents minor version updates. You should not enable this feature set on production clusters.

    Sample FeatureGate custom resource

    apiVersion: config.openshift.io/v1
    kind: FeatureGate
    metadata:
      name: cluster 1
    # ...
    spec:
      featureSet: TechPreviewNoUpgrade 2

    1
    The name of the FeatureGate CR must be cluster.
    2
    Add the feature set that you want to enable:
    • TechPreviewNoUpgrade enables specific Technology Preview features.

    After you save the changes, new machine configs are created, the machine config pools are updated, and scheduling on each node is disabled while the change is being applied.

Verification

You can verify that the feature gates are enabled by looking at the kubelet.conf file on a node after the nodes return to the ready state.

  1. From the Administrator perspective in the web console, navigate to ComputeNodes.
  2. Select a node.
  3. In the Node details page, click Terminal.
  4. In the terminal window, change your root directory to /host:

    sh-4.2# chroot /host
  5. View the kubelet.conf file:

    sh-4.2# cat /etc/kubernetes/kubelet.conf

    Sample output

    # ...
    featureGates:
      InsightsOperatorPullingSCA: true,
      LegacyNodeRoleBehavior: false
    # ...

    The features that are listed as true are enabled on your cluster.

    Note

    The features listed vary depending upon the OpenShift Container Platform version.

8.8. Improving cluster stability in high latency environments using worker latency profiles

If the cluster administrator has performed latency tests for platform verification, they can discover the need to adjust the operation of the cluster to ensure stability in cases of high latency. The cluster administrator need change only one parameter, recorded in a file, which controls four parameters affecting how supervisory processes read status and interpret the health of the cluster. Changing only the one parameter provides cluster tuning in an easy, supportable manner.

The Kubelet process provides the starting point for monitoring cluster health. The Kubelet sets status values for all nodes in the OpenShift Container Platform cluster. The Kubernetes Controller Manager (kube controller) reads the status values every 10 seconds, by default. If the kube controller cannot read a node status value, it loses contact with that node after a configured period. The default behavior is:

  1. The node controller on the control plane updates the node health to Unhealthy and marks the node Ready condition`Unknown`.
  2. In response, the scheduler stops scheduling pods to that node.
  3. The Node Lifecycle Controller adds a node.kubernetes.io/unreachable taint with a NoExecute effect to the node and schedules any pods on the node for eviction after five minutes, by default.

This behavior can cause problems if your network is prone to latency issues, especially if you have nodes at the network edge. In some cases, the Kubernetes Controller Manager might not receive an update from a healthy node due to network latency. The Kubelet evicts pods from the node even though the node is healthy.

To avoid this problem, you can use worker latency profiles to adjust the frequency that the Kubelet and the Kubernetes Controller Manager wait for status updates before taking action. These adjustments help to ensure that your cluster runs properly if network latency between the control plane and the worker nodes is not optimal.

These worker latency profiles contain three sets of parameters that are pre-defined with carefully tuned values to control the reaction of the cluster to increased latency. No need to experimentally find the best values manually.

You can configure worker latency profiles when installing a cluster or at any time you notice increased latency in your cluster network.

8.8.1. Understanding worker latency profiles

Worker latency profiles are four different categories of carefully-tuned parameters. The four parameters which implement these values are node-status-update-frequency, node-monitor-grace-period, default-not-ready-toleration-seconds and default-unreachable-toleration-seconds. These parameters can use values which allow you control the reaction of the cluster to latency issues without needing to determine the best values using manual methods.

Important

Setting these parameters manually is not supported. Incorrect parameter settings adversely affect cluster stability.

All worker latency profiles configure the following parameters:

node-status-update-frequency
Specifies how often the kubelet posts node status to the API server.
node-monitor-grace-period
Specifies the amount of time in seconds that the Kubernetes Controller Manager waits for an update from a kubelet before marking the node unhealthy and adding the node.kubernetes.io/not-ready or node.kubernetes.io/unreachable taint to the node.
default-not-ready-toleration-seconds
Specifies the amount of time in seconds after marking a node unhealthy that the Kube API Server Operator waits before evicting pods from that node.
default-unreachable-toleration-seconds
Specifies the amount of time in seconds after marking a node unreachable that the Kube API Server Operator waits before evicting pods from that node.

The following Operators monitor the changes to the worker latency profiles and respond accordingly:

  • The Machine Config Operator (MCO) updates the node-status-update-frequency parameter on the worker nodes.
  • The Kubernetes Controller Manager updates the node-monitor-grace-period parameter on the control plane nodes.
  • The Kubernetes API Server Operator updates the default-not-ready-toleration-seconds and default-unreachable-toleration-seconds parameters on the control plane nodes.

While the default configuration works in most cases, OpenShift Container Platform offers two other worker latency profiles for situations where the network is experiencing higher latency than usual. The three worker latency profiles are described in the following sections:

Default worker latency profile

With the Default profile, each Kubelet updates it’s status every 10 seconds (node-status-update-frequency). The Kube Controller Manager checks the statuses of Kubelet every 5 seconds (node-monitor-grace-period).

The Kubernetes Controller Manager waits 40 seconds for a status update from Kubelet before considering the Kubelet unhealthy. If no status is made available to the Kubernetes Controller Manager, it then marks the node with the node.kubernetes.io/not-ready or node.kubernetes.io/unreachable taint and evicts the pods on that node.

If a pod on that node has the NoExecute taint, the pod is run according to tolerationSeconds. If the pod has no taint, it will be evicted in 300 seconds (default-not-ready-toleration-seconds and default-unreachable-toleration-seconds settings of the Kube API Server).

ProfileComponentParameterValue

Default

kubelet

node-status-update-frequency

10s

Kubelet Controller Manager

node-monitor-grace-period

40s

Kubernetes API Server Operator

default-not-ready-toleration-seconds

300s

Kubernetes API Server Operator

default-unreachable-toleration-seconds

300s

Medium worker latency profile

Use the MediumUpdateAverageReaction profile if the network latency is slightly higher than usual.

The MediumUpdateAverageReaction profile reduces the frequency of kubelet updates to 20 seconds and changes the period that the Kubernetes Controller Manager waits for those updates to 2 minutes. The pod eviction period for a pod on that node is reduced to 60 seconds. If the pod has the tolerationSeconds parameter, the eviction waits for the period specified by that parameter.

The Kubernetes Controller Manager waits for 2 minutes to consider a node unhealthy. In another minute, the eviction process starts.

ProfileComponentParameterValue

MediumUpdateAverageReaction

kubelet

node-status-update-frequency

20s

Kubelet Controller Manager

node-monitor-grace-period

2m

Kubernetes API Server Operator

default-not-ready-toleration-seconds

60s

Kubernetes API Server Operator

default-unreachable-toleration-seconds

60s

Low worker latency profile

Use the LowUpdateSlowReaction profile if the network latency is extremely high.

The LowUpdateSlowReaction profile reduces the frequency of kubelet updates to 1 minute and changes the period that the Kubernetes Controller Manager waits for those updates to 5 minutes. The pod eviction period for a pod on that node is reduced to 60 seconds. If the pod has the tolerationSeconds parameter, the eviction waits for the period specified by that parameter.

The Kubernetes Controller Manager waits for 5 minutes to consider a node unhealthy. In another minute, the eviction process starts.

ProfileComponentParameterValue

LowUpdateSlowReaction

kubelet

node-status-update-frequency

1m

Kubelet Controller Manager

node-monitor-grace-period

5m

Kubernetes API Server Operator

default-not-ready-toleration-seconds

60s

Kubernetes API Server Operator

default-unreachable-toleration-seconds

60s

8.8.2. Using and changing worker latency profiles

To change a worker latency profile to deal with network latency, edit the node.config object to add the name of the profile. You can change the profile at any time as latency increases or decreases.

You must move one worker latency profile at a time. For example, you cannot move directly from the Default profile to the LowUpdateSlowReaction worker latency profile. You must move from the Default worker latency profile to the MediumUpdateAverageReaction profile first, then to LowUpdateSlowReaction. Similarly, when returning to the Default profile, you must move from the low profile to the medium profile first, then to Default.

Note

You can also configure worker latency profiles upon installing an OpenShift Container Platform cluster.

Procedure

To move from the default worker latency profile:

  1. Move to the medium worker latency profile:

    1. Edit the node.config object:

      $ oc edit nodes.config/cluster
    2. Add spec.workerLatencyProfile: MediumUpdateAverageReaction:

      Example node.config object

      apiVersion: config.openshift.io/v1
      kind: Node
      metadata:
        annotations:
          include.release.openshift.io/ibm-cloud-managed: "true"
          include.release.openshift.io/self-managed-high-availability: "true"
          include.release.openshift.io/single-node-developer: "true"
          release.openshift.io/create-only: "true"
        creationTimestamp: "2022-07-08T16:02:51Z"
        generation: 1
        name: cluster
        ownerReferences:
        - apiVersion: config.openshift.io/v1
          kind: ClusterVersion
          name: version
          uid: 36282574-bf9f-409e-a6cd-3032939293eb
        resourceVersion: "1865"
        uid: 0c0f7a4c-4307-4187-b591-6155695ac85b
      spec:
        workerLatencyProfile: MediumUpdateAverageReaction 1
      
      # ...

      1
      Specifies the medium worker latency policy.

      Scheduling on each worker node is disabled as the change is being applied.

  2. Optional: Move to the low worker latency profile:

    1. Edit the node.config object:

      $ oc edit nodes.config/cluster
    2. Change the spec.workerLatencyProfile value to LowUpdateSlowReaction:

      Example node.config object

      apiVersion: config.openshift.io/v1
      kind: Node
      metadata:
        annotations:
          include.release.openshift.io/ibm-cloud-managed: "true"
          include.release.openshift.io/self-managed-high-availability: "true"
          include.release.openshift.io/single-node-developer: "true"
          release.openshift.io/create-only: "true"
        creationTimestamp: "2022-07-08T16:02:51Z"
        generation: 1
        name: cluster
        ownerReferences:
        - apiVersion: config.openshift.io/v1
          kind: ClusterVersion
          name: version
          uid: 36282574-bf9f-409e-a6cd-3032939293eb
        resourceVersion: "1865"
        uid: 0c0f7a4c-4307-4187-b591-6155695ac85b
      spec:
        workerLatencyProfile: LowUpdateSlowReaction 1
      
      # ...

      1
      Specifies use of the low worker latency policy.

Scheduling on each worker node is disabled as the change is being applied.

Verification

  • When all nodes return to the Ready condition, you can use the following command to look in the Kubernetes Controller Manager to ensure it was applied:

    $ oc get KubeControllerManager -o yaml | grep -i workerlatency -A 5 -B 5

    Example output

    # ...
        - lastTransitionTime: "2022-07-11T19:47:10Z"
          reason: ProfileUpdated
          status: "False"
          type: WorkerLatencyProfileProgressing
        - lastTransitionTime: "2022-07-11T19:47:10Z" 1
          message: all static pod revision(s) have updated latency profile
          reason: ProfileUpdated
          status: "True"
          type: WorkerLatencyProfileComplete
        - lastTransitionTime: "2022-07-11T19:20:11Z"
          reason: AsExpected
          status: "False"
          type: WorkerLatencyProfileDegraded
        - lastTransitionTime: "2022-07-11T19:20:36Z"
          status: "False"
    # ...

    1
    Specifies that the profile is applied and active.

To change the medium profile to default or change the default to medium, edit the node.config object and set the spec.workerLatencyProfile parameter to the appropriate value.

Chapter 9. Remote worker nodes on the network edge

9.1. Using remote worker nodes at the network edge

You can configure OpenShift Container Platform clusters with nodes located at your network edge. In this topic, they are called remote worker nodes. A typical cluster with remote worker nodes combines on-premise master and worker nodes with worker nodes in other locations that connect to the cluster. This topic is intended to provide guidance on best practices for using remote worker nodes and does not contain specific configuration details.

There are multiple use cases across different industries, such as telecommunications, retail, manufacturing, and government, for using a deployment pattern with remote worker nodes. For example, you can separate and isolate your projects and workloads by combining the remote worker nodes into Kubernetes zones.

However, having remote worker nodes can introduce higher latency, intermittent loss of network connectivity, and other issues. Among the challenges in a cluster with remote worker node are:

  • Network separation: The OpenShift Container Platform control plane and the remote worker nodes must be able communicate with each other. Because of the distance between the control plane and the remote worker nodes, network issues could prevent this communication. See Network separation with remote worker nodes for information on how OpenShift Container Platform responds to network separation and for methods to diminish the impact to your cluster.
  • Power outage: Because the control plane and remote worker nodes are in separate locations, a power outage at the remote location or at any point between the two can negatively impact your cluster. See Power loss on remote worker nodes for information on how OpenShift Container Platform responds to a node losing power and for methods to diminish the impact to your cluster.
  • Latency spikes or temporary reduction in throughput: As with any network, any changes in network conditions between your cluster and the remote worker nodes can negatively impact your cluster. OpenShift Container Platform offers multiple worker latency profiles that let you control the reaction of the cluster to latency issues.

Note the following limitations when planning a cluster with remote worker nodes:

  • OpenShift Container Platform does not support remote worker nodes that use a different cloud provider than the on-premise cluster uses.
  • Moving workloads from one Kubernetes zone to a different Kubernetes zone can be problematic due to system and environment issues, such as a specific type of memory not being available in a different zone.
  • Proxies and firewalls can present additional limitations that are beyond the scope of this document. See the relevant OpenShift Container Platform documentation for how to address such limitations, such as Configuring your firewall.
  • You are responsible for configuring and maintaining L2/L3-level network connectivity between the control plane and the network-edge nodes.

9.1.1. Adding remote worker nodes

Adding remote worker nodes to a cluster involves some additional considerations.

  • You must ensure that a route or a default gateway is in place to route traffic between the control plane and every remote worker node.
  • You must place the Ingress VIP on the control plane.
  • Adding remote worker nodes with user-provisioned infrastructure is identical to adding other worker nodes.
  • To add remote worker nodes to an installer-provisioned cluster at install time, specify the subnet for each worker node in the install-config.yaml file before installation. There are no additional settings required for the DHCP server. You must use virtual media, because the remote worker nodes will not have access to the local provisioning network.
  • To add remote worker nodes to an installer-provisioned cluster deployed with a provisioning network, ensure that virtualMediaViaExternalNetwork flag is set to true in the install-config.yaml file so that it will add the nodes using virtual media. Remote worker nodes will not have access to the local provisioning network. They must be deployed with virtual media rather than PXE. Additionally, specify each subnet for each group of remote worker nodes and the control plane nodes in the DHCP server.

9.1.2. Network separation with remote worker nodes

All nodes send heartbeats to the Kubernetes Controller Manager Operator (kube controller) in the OpenShift Container Platform cluster every 10 seconds. If the cluster does not receive heartbeats from a node, OpenShift Container Platform responds using several default mechanisms.

OpenShift Container Platform is designed to be resilient to network partitions and other disruptions. You can mitigate some of the more common disruptions, such as interruptions from software upgrades, network splits, and routing issues. Mitigation strategies include ensuring that pods on remote worker nodes request the correct amount of CPU and memory resources, configuring an appropriate replication policy, using redundancy across zones, and using Pod Disruption Budgets on workloads.

If the kube controller loses contact with a node after a configured period, the node controller on the control plane updates the node health to Unhealthy and marks the node Ready condition as Unknown. In response, the scheduler stops scheduling pods to that node. The on-premise node controller adds a node.kubernetes.io/unreachable taint with a NoExecute effect to the node and schedules pods on the node for eviction after five minutes, by default.

If a workload controller, such as a Deployment object or StatefulSet object, is directing traffic to pods on the unhealthy node and other nodes can reach the cluster, OpenShift Container Platform routes the traffic away from the pods on the node. Nodes that cannot reach the cluster do not get updated with the new traffic routing. As a result, the workloads on those nodes might continue to attempt to reach the unhealthy node.

You can mitigate the effects of connection loss by:

  • using daemon sets to create pods that tolerate the taints
  • using static pods that automatically restart if a node goes down
  • using Kubernetes zones to control pod eviction
  • configuring pod tolerations to delay or avoid pod eviction
  • configuring the kubelet to control the timing of when it marks nodes as unhealthy.

For more information on using these objects in a cluster with remote worker nodes, see About remote worker node strategies.

9.1.3. Power loss on remote worker nodes

If a remote worker node loses power or restarts ungracefully, OpenShift Container Platform responds using several default mechanisms.

If the Kubernetes Controller Manager Operator (kube controller) loses contact with a node after a configured period, the control plane updates the node health to Unhealthy and marks the node Ready condition as Unknown. In response, the scheduler stops scheduling pods to that node. The on-premise node controller adds a node.kubernetes.io/unreachable taint with a NoExecute effect to the node and schedules pods on the node for eviction after five minutes, by default.

On the node, the pods must be restarted when the node recovers power and reconnects with the control plane.

Note

If you want the pods to restart immediately upon restart, use static pods.

After the node restarts, the kubelet also restarts and attempts to restart the pods that were scheduled on the node. If the connection to the control plane takes longer than the default five minutes, the control plane cannot update the node health and remove the node.kubernetes.io/unreachable taint. On the node, the kubelet terminates any running pods. When these conditions are cleared, the scheduler can start scheduling pods to that node.

You can mitigate the effects of power loss by:

  • using daemon sets to create pods that tolerate the taints
  • using static pods that automatically restart with a node
  • configuring pods tolerations to delay or avoid pod eviction
  • configuring the kubelet to control the timing of when the node controller marks nodes as unhealthy.

For more information on using these objects in a cluster with remote worker nodes, see About remote worker node strategies.

9.1.4. Latency spikes or temporary reduction in throughput to remote workers

If the cluster administrator has performed latency tests for platform verification, they can discover the need to adjust the operation of the cluster to ensure stability in cases of high latency. The cluster administrator need change only one parameter, recorded in a file, which controls four parameters affecting how supervisory processes read status and interpret the health of the cluster. Changing only the one parameter provides cluster tuning in an easy, supportable manner.

The Kubelet process provides the starting point for monitoring cluster health. The Kubelet sets status values for all nodes in the OpenShift Container Platform cluster. The Kubernetes Controller Manager (kube controller) reads the status values every 10 seconds, by default. If the kube controller cannot read a node status value, it loses contact with that node after a configured period. The default behavior is:

  1. The node controller on the control plane updates the node health to Unhealthy and marks the node Ready condition`Unknown`.
  2. In response, the scheduler stops scheduling pods to that node.
  3. The Node Lifecycle Controller adds a node.kubernetes.io/unreachable taint with a NoExecute effect to the node and schedules any pods on the node for eviction after five minutes, by default.

This behavior can cause problems if your network is prone to latency issues, especially if you have nodes at the network edge. In some cases, the Kubernetes Controller Manager might not receive an update from a healthy node due to network latency. The Kubelet evicts pods from the node even though the node is healthy.

To avoid this problem, you can use worker latency profiles to adjust the frequency that the Kubelet and the Kubernetes Controller Manager wait for status updates before taking action. These adjustments help to ensure that your cluster runs properly if network latency between the control plane and the worker nodes is not optimal.

These worker latency profiles contain three sets of parameters that are pre-defined with carefully tuned values to control the reaction of the cluster to increased latency. No need to experimentally find the best values manually.

You can configure worker latency profiles when installing a cluster or at any time you notice increased latency in your cluster network.

9.1.5. Remote worker node strategies

If you use remote worker nodes, consider which objects to use to run your applications.

It is recommended to use daemon sets or static pods based on the behavior you want in the event of network issues or power loss. In addition, you can use Kubernetes zones and tolerations to control or avoid pod evictions if the control plane cannot reach remote worker nodes.

Daemon sets
Daemon sets are the best approach to managing pods on remote worker nodes for the following reasons:
  • Daemon sets do not typically need rescheduling behavior. If a node disconnects from the cluster, pods on the node can continue to run. OpenShift Container Platform does not change the state of daemon set pods, and leaves the pods in the state they last reported. For example, if a daemon set pod is in the Running state, when a node stops communicating, the pod keeps running and is assumed to be running by OpenShift Container Platform.
  • Daemon set pods, by default, are created with NoExecute tolerations for the node.kubernetes.io/unreachable and node.kubernetes.io/not-ready taints with no tolerationSeconds value. These default values ensure that daemon set pods are never evicted if the control plane cannot reach a node. For example:

    Tolerations added to daemon set pods by default

      tolerations:
        - key: node.kubernetes.io/not-ready
          operator: Exists
          effect: NoExecute
        - key: node.kubernetes.io/unreachable
          operator: Exists
          effect: NoExecute
        - key: node.kubernetes.io/disk-pressure
          operator: Exists
          effect: NoSchedule
        - key: node.kubernetes.io/memory-pressure
          operator: Exists
          effect: NoSchedule
        - key: node.kubernetes.io/pid-pressure
          operator: Exists
          effect: NoSchedule
        - key: node.kubernetes.io/unschedulable
          operator: Exists
          effect: NoSchedule

  • Daemon sets can use labels to ensure that a workload runs on a matching worker node.
  • You can use an OpenShift Container Platform service endpoint to load balance daemon set pods.
Note

Daemon sets do not schedule pods after a reboot of the node if OpenShift Container Platform cannot reach the node.

Static pods
If you want pods restart if a node reboots, after a power loss for example, consider static pods. The kubelet on a node automatically restarts static pods as node restarts.
Note

Static pods cannot use secrets and config maps.

Kubernetes zones
Kubernetes zones can slow down the rate or, in some cases, completely stop pod evictions.

When the control plane cannot reach a node, the node controller, by default, applies node.kubernetes.io/unreachable taints and evicts pods at a rate of 0.1 nodes per second. However, in a cluster that uses Kubernetes zones, pod eviction behavior is altered.

If a zone is fully disrupted, where all nodes in the zone have a Ready condition that is False or Unknown, the control plane does not apply the node.kubernetes.io/unreachable taint to the nodes in that zone.

For partially disrupted zones, where more than 55% of the nodes have a False or Unknown condition, the pod eviction rate is reduced to 0.01 nodes per second. Nodes in smaller clusters, with fewer than 50 nodes, are not tainted. Your cluster must have more than three zones for these behavior to take effect.

You assign a node to a specific zone by applying the topology.kubernetes.io/region label in the node specification.

Sample node labels for Kubernetes zones

kind: Node
apiVersion: v1
metadata:
  labels:
    topology.kubernetes.io/region=east

KubeletConfig objects

You can adjust the amount of time that the kubelet checks the state of each node.

To set the interval that affects the timing of when the on-premise node controller marks nodes with the Unhealthy or Unreachable condition, create a KubeletConfig object that contains the node-status-update-frequency and node-status-report-frequency parameters.

The kubelet on each node determines the node status as defined by the node-status-update-frequency setting and reports that status to the cluster based on the node-status-report-frequency setting. By default, the kubelet determines the pod status every 10 seconds and reports the status every minute. However, if the node state changes, the kubelet reports the change to the cluster immediately. OpenShift Container Platform uses the node-status-report-frequency setting only when the Node Lease feature gate is enabled, which is the default state in OpenShift Container Platform clusters. If the Node Lease feature gate is disabled, the node reports its status based on the node-status-update-frequency setting.

Example kubelet config

apiVersion: machineconfiguration.openshift.io/v1
kind: KubeletConfig
metadata:
  name: disable-cpu-units
spec:
  machineConfigPoolSelector:
    matchLabels:
      machineconfiguration.openshift.io/role: worker 1
  kubeletConfig:
    node-status-update-frequency: 2
      - "10s"
    node-status-report-frequency: 3
      - "1m"

1
Specify the type of node type to which this KubeletConfig object applies using the label from the MachineConfig object.
2
Specify the frequency that the kubelet checks the status of a node associated with this MachineConfig object. The default value is 10s. If you change this default, the node-status-report-frequency value is changed to the same value.
3
Specify the frequency that the kubelet reports the status of a node associated with this MachineConfig object. The default value is 1m.

The node-status-update-frequency parameter works with the node-monitor-grace-period and pod-eviction-timeout parameters.

  • The node-monitor-grace-period parameter specifies how long OpenShift Container Platform waits after a node associated with a MachineConfig object is marked Unhealthy if the controller manager does not receive the node heartbeat. Workloads on the node continue to run after this time. If the remote worker node rejoins the cluster after node-monitor-grace-period expires, pods continue to run. New pods can be scheduled to that node. The node-monitor-grace-period interval is 40s. The node-status-update-frequency value must be lower than the node-monitor-grace-period value.
  • The pod-eviction-timeout parameter specifies the amount of time OpenShift Container Platform waits after marking a node that is associated with a MachineConfig object as Unreachable to start marking pods for eviction. Evicted pods are rescheduled on other nodes. If the remote worker node rejoins the cluster after pod-eviction-timeout expires, the pods running on the remote worker node are terminated because the node controller has evicted the pods on-premise. Pods can then be rescheduled to that node. The pod-eviction-timeout interval is 5m0s.
Note

Modifying the node-monitor-grace-period and pod-eviction-timeout parameters is not supported.

Tolerations
You can use pod tolerations to mitigate the effects if the on-premise node controller adds a node.kubernetes.io/unreachable taint with a NoExecute effect to a node it cannot reach.

A taint with the NoExecute effect affects pods that are running on the node in the following ways:

  • Pods that do not tolerate the taint are queued for eviction.
  • Pods that tolerate the taint without specifying a tolerationSeconds value in their toleration specification remain bound forever.
  • Pods that tolerate the taint with a specified tolerationSeconds value remain bound for the specified amount of time. After the time elapses, the pods are queued for eviction.

You can delay or avoid pod eviction by configuring pods tolerations with the NoExecute effect for the node.kubernetes.io/unreachable and node.kubernetes.io/not-ready taints.

Example toleration in a pod spec

...
tolerations:
- key: "node.kubernetes.io/unreachable"
  operator: "Exists"
  effect: "NoExecute" 1
- key: "node.kubernetes.io/not-ready"
  operator: "Exists"
  effect: "NoExecute" 2
  tolerationSeconds: 600
...

1
The NoExecute effect without tolerationSeconds lets pods remain forever if the control plane cannot reach the node.
2
The NoExecute effect with tolerationSeconds: 600 lets pods remain for 10 minutes if the control plane marks the node as Unhealthy.

OpenShift Container Platform uses the tolerationSeconds value after the pod-eviction-timeout value elapses.

Other types of OpenShift Container Platform objects
You can use replica sets, deployments, and replication controllers. The scheduler can reschedule these pods onto other nodes after the node is disconnected for five minutes. Rescheduling onto other nodes can be beneficial for some workloads, such as REST APIs, where an administrator can guarantee a specific number of pods are running and accessible.
Note

When working with remote worker nodes, rescheduling pods on different nodes might not be acceptable if remote worker nodes are intended to be reserved for specific functions.

stateful sets do not get restarted when there is an outage. The pods remain in the terminating state until the control plane can acknowledge that the pods are terminated.

To avoid scheduling a to a node that does not have access to the same type of persistent storage, OpenShift Container Platform cannot migrate pods that require persistent volumes to other zones in the case of network separation.

Additional resources

Chapter 10. Worker nodes for single-node OpenShift clusters

10.1. Adding worker nodes to single-node OpenShift clusters

Single-node OpenShift clusters reduce the host prerequisites for deployment to a single host. This is useful for deployments in constrained environments or at the network edge. However, sometimes you need to add additional capacity to your cluster, for example, in telecommunications and network edge scenarios. In these scenarios, you can add worker nodes to the single-node cluster.

There are several ways that you can add worker nodes to a single-node cluster. You can add worker nodes to a cluster manually, using Red Hat OpenShift Cluster Manager, or by using the Assisted Installer REST API directly.

Important

Adding worker nodes does not expand the cluster control plane, and it does not provide high availability to your cluster. For single-node OpenShift clusters, high availability is handled by failing over to another site. It is not recommended to add a large number of worker nodes to a single-node cluster.

Note

Unlike multi-node clusters, by default all ingress traffic is routed to the single control-plane node, even after adding additional worker nodes.

10.1.1. Requirements for installing single-node OpenShift worker nodes

To install a single-node OpenShift worker node, you must address the following requirements:

  • Administration host: You must have a computer to prepare the ISO and to monitor the installation.
  • Production-grade server: Installing single-node OpenShift worker nodes requires a server with sufficient resources to run OpenShift Container Platform services and a production workload.

    Table 10.1. Minimum resource requirements
    ProfilevCPUMemoryStorage

    Minimum

    2 vCPU cores

    8GB of RAM

    100GB

    Note

    One vCPU is equivalent to one physical core when simultaneous multithreading (SMT), or hyperthreading, is not enabled. When enabled, use the following formula to calculate the corresponding ratio:

    (threads per core × cores) × sockets = vCPUs

    The server must have a Baseboard Management Controller (BMC) when booting with virtual media.

  • Networking: The worker node server must have access to the internet or access to a local registry if it is not connected to a routable network. The worker node server must have a DHCP reservation or a static IP address and be able to access the single-node OpenShift cluster Kubernetes API, ingress route, and cluster node domain names. You must configure the DNS to resolve the IP address to each of the following fully qualified domain names (FQDN) for the single-node OpenShift cluster:

    Table 10.2. Required DNS records
    UsageFQDNDescription

    Kubernetes API

    api.<cluster_name>.<base_domain>

    Add a DNS A/AAAA or CNAME record. This record must be resolvable by clients external to the cluster.

    Internal API

    api-int.<cluster_name>.<base_domain>

    Add a DNS A/AAAA or CNAME record when creating the ISO manually. This record must be resolvable by nodes within the cluster.

    Ingress route

    *.apps.<cluster_name>.<base_domain>

    Add a wildcard DNS A/AAAA or CNAME record that targets the node. This record must be resolvable by clients external to the cluster.

    Without persistent IP addresses, communications between the apiserver and etcd might fail.

10.1.2. Adding worker nodes using the Assisted Installer and OpenShift Cluster Manager

You can add worker nodes to single-node OpenShift clusters that were created on Red Hat OpenShift Cluster Manager using the Assisted Installer.

Important

Adding worker nodes to single-node OpenShift clusters is only supported for clusters running OpenShift Container Platform version 4.11 and up.

Prerequisites

  • Have access to a single-node OpenShift cluster installed using Assisted Installer.
  • Install the OpenShift CLI (oc).
  • Log in as a user with cluster-admin privileges.
  • Ensure that all the required DNS records exist for the cluster that you are adding the worker node to.

Procedure

  1. Log in to OpenShift Cluster Manager and click the single-node cluster that you want to add a worker node to.
  2. Click Add hosts, and download the discovery ISO for the new worker node, adding SSH public key and configuring cluster-wide proxy settings as required.
  3. Boot the target host using the discovery ISO, and wait for the host to be discovered in the console. After the host is discovered, start the installation.
  4. As the installation proceeds, the installation generates pending certificate signing requests (CSRs) for the worker node. When prompted, approve the pending CSRs to complete the installation.

    When the worker node is sucessfully installed, it is listed as a worker node in the cluster web console.

Important

New worker nodes will be encrypted using the same method as the original cluster.

10.1.3. Adding worker nodes using the Assisted Installer API

You can add worker nodes to single-node OpenShift clusters using the Assisted Installer REST API. Before you add worker nodes, you must log in to OpenShift Cluster Manager and authenticate against the API.

10.1.3.1. Authenticating against the Assisted Installer REST API

Before you can use the Assisted Installer REST API, you must authenticate against the API using a JSON web token (JWT) that you generate.

Prerequisites

Procedure

  1. Log in to OpenShift Cluster Manager and copy your API token.
  2. Set the $OFFLINE_TOKEN variable using the copied API token by running the following command:

    $ export OFFLINE_TOKEN=<copied_api_token>
  3. Set the $JWT_TOKEN variable using the previously set $OFFLINE_TOKEN variable:

    $ export JWT_TOKEN=$(
      curl \
      --silent \
      --header "Accept: application/json" \
      --header "Content-Type: application/x-www-form-urlencoded" \
      --data-urlencode "grant_type=refresh_token" \
      --data-urlencode "client_id=cloud-services" \
      --data-urlencode "refresh_token=${OFFLINE_TOKEN}" \
      "https://sso.redhat.com/auth/realms/redhat-external/protocol/openid-connect/token" \
      | jq --raw-output ".access_token"
    )
    Note

    The JWT token is valid for 15 minutes only.

Verification

  • Optional: Check that you can access the API by running the following command:

    $ curl -s https://api.openshift.com/api/assisted-install/v2/component-versions -H "Authorization: Bearer ${JWT_TOKEN}" | jq

    Example output

    {
        "release_tag": "v2.5.1",
        "versions":
        {
            "assisted-installer": "registry.redhat.io/rhai-tech-preview/assisted-installer-rhel8:v1.0.0-175",
            "assisted-installer-controller": "registry.redhat.io/rhai-tech-preview/assisted-installer-reporter-rhel8:v1.0.0-223",
            "assisted-installer-service": "quay.io/app-sre/assisted-service:ac87f93",
            "discovery-agent": "registry.redhat.io/rhai-tech-preview/assisted-installer-agent-rhel8:v1.0.0-156"
        }
    }

10.1.3.2. Adding worker nodes using the Assisted Installer REST API

You can add worker nodes to clusters using the Assisted Installer REST API.

Prerequisites

  • Install the OpenShift Cluster Manager CLI (ocm).
  • Log in to OpenShift Cluster Manager as a user with cluster creation privileges.
  • Install jq.
  • Ensure that all the required DNS records exist for the cluster that you are adding the worker node to.

Procedure

  1. Authenticate against the Assisted Installer REST API and generate a JSON web token (JWT) for your session. The generated JWT token is valid for 15 minutes only.
  2. Set the $API_URL variable by running the following command:

    $ export API_URL=<api_url> 1
    1
    Replace <api_url> with the Assisted Installer API URL, for example, https://api.openshift.com
  3. Import the single-node OpenShift cluster by running the following commands:

    1. Set the $OPENSHIFT_CLUSTER_ID variable. Log in to the cluster and run the following command:

      $ export OPENSHIFT_CLUSTER_ID=$(oc get clusterversion -o jsonpath='{.items[].spec.clusterID}')
    2. Set the $CLUSTER_REQUEST variable that is used to import the cluster:

      $ export CLUSTER_REQUEST=$(jq --null-input --arg openshift_cluster_id "$OPENSHIFT_CLUSTER_ID" '{
        "api_vip_dnsname": "<api_vip>", 1
        "openshift_cluster_id": $openshift_cluster_id,
        "name": "<openshift_cluster_name>" 2
      }')
      1
      Replace <api_vip> with the hostname for the cluster’s API server. This can be the DNS domain for the API server or the IP address of the single node which the worker node can reach. For example, api.compute-1.example.com.
      2
      Replace <openshift_cluster_name> with the plain text name for the cluster. The cluster name should match the cluster name that was set during the Day 1 cluster installation.
    3. Import the cluster and set the $CLUSTER_ID variable. Run the following command:

      $ CLUSTER_ID=$(curl "$API_URL/api/assisted-install/v2/clusters/import" -H "Authorization: Bearer ${JWT_TOKEN}" -H 'accept: application/json' -H 'Content-Type: application/json' \
        -d "$CLUSTER_REQUEST" | tee /dev/stderr | jq -r '.id')
  4. Generate the InfraEnv resource for the cluster and set the $INFRA_ENV_ID variable by running the following commands:

    1. Download the pull secret file from Red Hat OpenShift Cluster Manager at console.redhat.com.
    2. Set the $INFRA_ENV_REQUEST variable:

      export INFRA_ENV_REQUEST=$(jq --null-input \
          --slurpfile pull_secret <path_to_pull_secret_file> \1
          --arg ssh_pub_key "$(cat <path_to_ssh_pub_key>)" \2
          --arg cluster_id "$CLUSTER_ID" '{
        "name": "<infraenv_name>", 3
        "pull_secret": $pull_secret[0] | tojson,
        "cluster_id": $cluster_id,
        "ssh_authorized_key": $ssh_pub_key,
        "image_type": "<iso_image_type>" 4
      }')
      1
      Replace <path_to_pull_secret_file> with the path to the local file containing the downloaded pull secret from Red Hat OpenShift Cluster Manager at console.redhat.com.
      2
      Replace <path_to_ssh_pub_key> with the path to the public SSH key required to access the host. If you do not set this value, you cannot access the host while in discovery mode.
      3
      Replace <infraenv_name> with the plain text name for the InfraEnv resource.
      4
      Replace <iso_image_type> with the ISO image type, either full-iso or minimal-iso.
    3. Post the $INFRA_ENV_REQUEST to the /v2/infra-envs API and set the $INFRA_ENV_ID variable:

      $ INFRA_ENV_ID=$(curl "$API_URL/api/assisted-install/v2/infra-envs" -H "Authorization: Bearer ${JWT_TOKEN}" -H 'accept: application/json' -H 'Content-Type: application/json' -d "$INFRA_ENV_REQUEST" | tee /dev/stderr | jq -r '.id')
  5. Get the URL of the discovery ISO for the cluster worker node by running the following command:

    $ curl -s "$API_URL/api/assisted-install/v2/infra-envs/$INFRA_ENV_ID" -H "Authorization: Bearer ${JWT_TOKEN}" | jq -r '.download_url'

    Example output

    https://api.openshift.com/api/assisted-images/images/41b91e72-c33e-42ee-b80f-b5c5bbf6431a?arch=x86_64&image_token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE2NTYwMjYzNzEsInN1YiI6IjQxYjkxZTcyLWMzM2UtNDJlZS1iODBmLWI1YzViYmY2NDMxYSJ9.1EX_VGaMNejMhrAvVRBS7PDPIQtbOOc8LtG8OukE1a4&type=minimal-iso&version=4.12

  6. Download the ISO:

    $ curl -L -s '<iso_url>' --output rhcos-live-minimal.iso 1
    1
    Replace <iso_url> with the URL for the ISO from the previous step.
  7. Boot the new worker host from the downloaded rhcos-live-minimal.iso.
  8. Get the list of hosts in the cluster that are not installed. Keep running the following command until the new host shows up:

    $ curl -s "$API_URL/api/assisted-install/v2/clusters/$CLUSTER_ID" -H "Authorization: Bearer ${JWT_TOKEN}" | jq -r '.hosts[] | select(.status != "installed").id'

    Example output

    2294ba03-c264-4f11-ac08-2f1bb2f8c296

  9. Set the $HOST_ID variable for the new worker node, for example:

    $ HOST_ID=<host_id> 1
    1
    Replace <host_id> with the host ID from the previous step.
  10. Check that the host is ready to install by running the following command:

    Note

    Ensure that you copy the entire command including the complete jq expression.

    $ curl -s $API_URL/api/assisted-install/v2/clusters/$CLUSTER_ID -H "Authorization: Bearer ${JWT_TOKEN}" | jq '
    def host_name($host):
        if (.suggested_hostname // "") == "" then
            if (.inventory // "") == "" then
                "Unknown hostname, please wait"
            else
                .inventory | fromjson | .hostname
            end
        else
            .suggested_hostname
        end;
    
    def is_notable($validation):
        ["failure", "pending", "error"] | any(. == $validation.status);
    
    def notable_validations($validations_info):
        [
            $validations_info // "{}"
            | fromjson
            | to_entries[].value[]
            | select(is_notable(.))
        ];
    
    {
        "Hosts validations": {
            "Hosts": [
                .hosts[]
                | select(.status != "installed")
                | {
                    "id": .id,
                    "name": host_name(.),
                    "status": .status,
                    "notable_validations": notable_validations(.validations_info)
                }
            ]
        },
        "Cluster validations info": {
            "notable_validations": notable_validations(.validations_info)
        }
    }
    ' -r

    Example output

    {
      "Hosts validations": {
        "Hosts": [
          {
            "id": "97ec378c-3568-460c-bc22-df54534ff08f",
            "name": "localhost.localdomain",
            "status": "insufficient",
            "notable_validations": [
              {
                "id": "ntp-synced",
                "status": "failure",
                "message": "Host couldn't synchronize with any NTP server"
              },
              {
                "id": "api-domain-name-resolved-correctly",
                "status": "error",
                "message": "Parse error for domain name resolutions result"
              },
              {
                "id": "api-int-domain-name-resolved-correctly",
                "status": "error",
                "message": "Parse error for domain name resolutions result"
              },
              {
                "id": "apps-domain-name-resolved-correctly",
                "status": "error",
                "message": "Parse error for domain name resolutions result"
              }
            ]
          }
        ]
      },
      "Cluster validations info": {
        "notable_validations": []
      }
    }

  11. When the previous command shows that the host is ready, start the installation using the /v2/infra-envs/{infra_env_id}/hosts/{host_id}/actions/install API by running the following command:

    $ curl -X POST -s "$API_URL/api/assisted-install/v2/infra-envs/$INFRA_ENV_ID/hosts/$HOST_ID/actions/install"  -H "Authorization: Bearer ${JWT_TOKEN}"
  12. As the installation proceeds, the installation generates pending certificate signing requests (CSRs) for the worker node.

    Important

    You must approve the CSRs to complete the installation.

    Keep running the following API call to monitor the cluster installation:

    $ curl -s "$API_URL/api/assisted-install/v2/clusters/$CLUSTER_ID" -H "Authorization: Bearer ${JWT_TOKEN}" | jq '{
        "Cluster day-2 hosts":
            [
                .hosts[]
                | select(.status != "installed")
                | {id, requested_hostname, status, status_info, progress, status_updated_at, updated_at, infra_env_id, cluster_id, created_at}
            ]
    }'

    Example output

    {
      "Cluster day-2 hosts": [
        {
          "id": "a1c52dde-3432-4f59-b2ae-0a530c851480",
          "requested_hostname": "control-plane-1",
          "status": "added-to-existing-cluster",
          "status_info": "Host has rebooted and no further updates will be posted. Please check console for progress and to possibly approve pending CSRs",
          "progress": {
            "current_stage": "Done",
            "installation_percentage": 100,
            "stage_started_at": "2022-07-08T10:56:20.476Z",
            "stage_updated_at": "2022-07-08T10:56:20.476Z"
          },
          "status_updated_at": "2022-07-08T10:56:20.476Z",
          "updated_at": "2022-07-08T10:57:15.306369Z",
          "infra_env_id": "b74ec0c3-d5b5-4717-a866-5b6854791bd3",
          "cluster_id": "8f721322-419d-4eed-aa5b-61b50ea586ae",
          "created_at": "2022-07-06T22:54:57.161614Z"
        }
      ]
    }

  13. Optional: Run the following command to see all the events for the cluster:

    $ curl -s "$API_URL/api/assisted-install/v2/events?cluster_id=$CLUSTER_ID" -H "Authorization: Bearer ${JWT_TOKEN}" | jq -c '.[] | {severity, message, event_time, host_id}'

    Example output

    {"severity":"info","message":"Host compute-0: updated status from insufficient to known (Host is ready to be installed)","event_time":"2022-07-08T11:21:46.346Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}
    {"severity":"info","message":"Host compute-0: updated status from known to installing (Installation is in progress)","event_time":"2022-07-08T11:28:28.647Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}
    {"severity":"info","message":"Host compute-0: updated status from installing to installing-in-progress (Starting installation)","event_time":"2022-07-08T11:28:52.068Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}
    {"severity":"info","message":"Uploaded logs for host compute-0 cluster 8f721322-419d-4eed-aa5b-61b50ea586ae","event_time":"2022-07-08T11:29:47.802Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}
    {"severity":"info","message":"Host compute-0: updated status from installing-in-progress to added-to-existing-cluster (Host has rebooted and no further updates will be posted. Please check console for progress and to possibly approve pending CSRs)","event_time":"2022-07-08T11:29:48.259Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}
    {"severity":"info","message":"Host: compute-0, reached installation stage Rebooting","event_time":"2022-07-08T11:29:48.261Z","host_id":"9d7b3b44-1125-4ad0-9b14-76550087b445"}

  14. Log in to the cluster and approve the pending CSRs to complete the installation.

Verification

  • Check that the new worker node was successfully added to the cluster with a status of Ready:

    $ oc get nodes

    Example output

    NAME                           STATUS   ROLES           AGE   VERSION
    control-plane-1.example.com    Ready    master,worker   56m   v1.25.0
    compute-1.example.com          Ready    worker          11m   v1.25.0

10.1.4. Adding worker nodes to single-node OpenShift clusters manually

You can add a worker node to a single-node OpenShift cluster manually by booting the worker node from Red Hat Enterprise Linux CoreOS (RHCOS) ISO and by using the cluster worker.ign file to join the new worker node to the cluster.

Prerequisites

  • Install a single-node OpenShift cluster on bare metal.
  • Install the OpenShift CLI (oc).
  • Log in as a user with cluster-admin privileges.
  • Ensure that all the required DNS records exist for the cluster that you are adding the worker node to.

Procedure

  1. Set the OpenShift Container Platform version:

    $ OCP_VERSION=<ocp_version> 1
    1
    Replace <ocp_version> with the current version, for example, latest-4.12
  2. Set the host architecture:

    $ ARCH=<architecture> 1
    1
    Replace <architecture> with the target host architecture, for example, aarch64 or x86_64.
  3. Get the worker.ign data from the running single-node cluster by running the following command:

    $ oc extract -n openshift-machine-api secret/worker-user-data-managed --keys=userData --to=- > worker.ign
  4. Host the worker.ign file on a web server accessible from your network.
  5. Download the OpenShift Container Platform installer and make it available for use by running the following commands:

    $ curl -k https://mirror.openshift.com/pub/openshift-v4/clients/ocp/$OCP_VERSION/openshift-install-linux.tar.gz > openshift-install-linux.tar.gz
    $ tar zxvf openshift-install-linux.tar.gz
    $ chmod +x openshift-install
  6. Retrieve the RHCOS ISO URL:

    $ ISO_URL=$(./openshift-install coreos print-stream-json | grep location | grep $ARCH | grep iso | cut -d\" -f4)
  7. Download the RHCOS ISO:

    $ curl -L $ISO_URL -o rhcos-live.iso
  8. Use the RHCOS ISO and the hosted worker.ign file to install the worker node:

    1. Boot the target host with the RHCOS ISO and your preferred method of installation.
    2. When the target host has booted from the RHCOS ISO, open a console on the target host.
    3. If your local network does not have DHCP enabled, you need to create an ignition file with the new hostname and configure the worker node static IP address before running the RHCOS installation. Perform the following steps:

      1. Configure the worker host network connection with a static IP. Run the following command on the target host console:

        $ nmcli con mod <network_interface> ipv4.method manual /
        ipv4.addresses <static_ip> ipv4.gateway <network_gateway> ipv4.dns <dns_server> /
        802-3-ethernet.mtu 9000

        where:

        <static_ip>
        Is the host static IP address and CIDR, for example, 10.1.101.50/24
        <network_gateway>
        Is the network gateway, for example, 10.1.101.1
      2. Activate the modified network interface:

        $ nmcli con up <network_interface>
      3. Create a new ignition file new-worker.ign that includes a reference to the original worker.ign and an additional instruction that the coreos-installer program uses to populate the /etc/hostname file on the new worker host. For example:

        {
          "ignition":{
            "version":"3.2.0",
            "config":{
              "merge":[
                {
                  "source":"<hosted_worker_ign_file>" 1
                }
              ]
            }
          },
          "storage":{
            "files":[
              {
                "path":"/etc/hostname",
                "contents":{
                  "source":"data:,<new_fqdn>" 2
                },
                "mode":420,
                "overwrite":true,
                "path":"/etc/hostname"
              }
            ]
          }
        }
        1
        <hosted_worker_ign_file> is the locally accessible URL for the original worker.ign file. For example, http://webserver.example.com/worker.ign
        2
        <new_fqdn> is the new FQDN that you set for the worker node. For example, new-worker.example.com.
      4. Host the new-worker.ign file on a web server accessible from your network.
      5. Run the following coreos-installer command, passing in the ignition-url and hard disk details:

        $ sudo coreos-installer install --copy-network /
        --ignition-url=<new_worker_ign_file> <hard_disk> --insecure-ignition

        where:

        <new_worker_ign_file>
        is the locally accessible URL for the hosted new-worker.ign file, for example, http://webserver.example.com/new-worker.ign
        <hard_disk>
        Is the hard disk where you install RHCOS, for example, /dev/sda
    4. For networks that have DHCP enabled, you do not need to set a static IP. Run the following coreos-installer command from the target host console to install the system:

      $ coreos-installer install --ignition-url=<hosted_worker_ign_file> <hard_disk>
    5. To manually enable DHCP, apply the following NMStateConfig CR to the single-node OpenShift cluster:

      apiVersion: agent-install.openshift.io/v1
      kind: NMStateConfig
      metadata:
        name: nmstateconfig-dhcp
        namespace: example-sno
        labels:
          nmstate_config_cluster_name: <nmstate_config_cluster_label>
      spec:
        config:
          interfaces:
            - name: eth0
              type: ethernet
              state: up
              ipv4:
                enabled: true
                dhcp: true
              ipv6:
                enabled: false
        interfaces:
          - name: "eth0"
            macAddress: "AA:BB:CC:DD:EE:11"
      Important

      The NMStateConfig CR is required for successful deployments of worker nodes with static IP addresses and for adding a worker node with a dynamic IP address if the single-node OpenShift was deployed with a static IP address. The cluster network DHCP does not automatically set these network settings for the new worker node.

  9. As the installation proceeds, the installation generates pending certificate signing requests (CSRs) for the worker node. When prompted, approve the pending CSRs to complete the installation.
  10. When the install is complete, reboot the host. The host joins the cluster as a new worker node.

Verification

  • Check that the new worker node was successfully added to the cluster with a status of Ready:

    $ oc get nodes

    Example output

    NAME                           STATUS   ROLES           AGE   VERSION
    control-plane-1.example.com    Ready    master,worker   56m   v1.25.0
    compute-1.example.com          Ready    worker          11m   v1.25.0

10.1.5. Approving the certificate signing requests for your machines

When you add machines to a cluster, two pending certificate signing requests (CSRs) are generated for each machine that you added. You must confirm that these CSRs are approved or, if necessary, approve them yourself. The client requests must be approved first, followed by the server requests.

Prerequisites

  • You added machines to your cluster.

Procedure

  1. Confirm that the cluster recognizes the machines:

    $ oc get nodes

    Example output

    NAME      STATUS    ROLES   AGE  VERSION
    master-0  Ready     master  63m  v1.25.0
    master-1  Ready     master  63m  v1.25.0
    master-2  Ready     master  64m  v1.25.0

    The output lists all of the machines that you created.

    Note

    The preceding output might not include the compute nodes, also known as worker nodes, until some CSRs are approved.

  2. Review the pending CSRs and ensure that you see the client requests with the Pending or Approved status for each machine that you added to the cluster:

    $ oc get csr

    Example output

    NAME        AGE     REQUESTOR                                                                   CONDITION
    csr-8b2br   15m     system:serviceaccount:openshift-machine-config-operator:node-bootstrapper   Pending
    csr-8vnps   15m     system:serviceaccount:openshift-machine-config-operator:node-bootstrapper   Pending
    ...

    In this example, two machines are joining the cluster. You might see more approved CSRs in the list.

  3. If the CSRs were not approved, after all of the pending CSRs for the machines you added are in Pending status, approve the CSRs for your cluster machines:

    Note

    Because the CSRs rotate automatically, approve your CSRs within an hour of adding the machines to the cluster. If you do not approve them within an hour, the certificates will rotate, and more than two certificates will be present for each node. You must approve all of these certificates. After the client CSR is approved, the Kubelet creates a secondary CSR for the serving certificate, which requires manual approval. Then, subsequent serving certificate renewal requests are automatically approved by the machine-approver if the Kubelet requests a new certificate with identical parameters.

    Note

    For clusters running on platforms that are not machine API enabled, such as bare metal and other user-provisioned infrastructure, you must implement a method of automatically approving the kubelet serving certificate requests (CSRs). If a request is not approved, then the oc exec, oc rsh, and oc logs commands cannot succeed, because a serving certificate is required when the API server connects to the kubelet. Any operation that contacts the Kubelet endpoint requires this certificate approval to be in place. The method must watch for new CSRs, confirm that the CSR was submitted by the node-bootstrapper service account in the system:node or system:admin groups, and confirm the identity of the node.

    • To approve them individually, run the following command for each valid CSR:

      $ oc adm certificate approve <csr_name> 1
      1
      <csr_name> is the name of a CSR from the list of current CSRs.
    • To approve all pending CSRs, run the following command:

      $ oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs --no-run-if-empty oc adm certificate approve
      Note

      Some Operators might not become available until some CSRs are approved.

  4. Now that your client requests are approved, you must review the server requests for each machine that you added to the cluster:

    $ oc get csr

    Example output

    NAME        AGE     REQUESTOR                                                                   CONDITION
    csr-bfd72   5m26s   system:node:ip-10-0-50-126.us-east-2.compute.internal                       Pending
    csr-c57lv   5m26s   system:node:ip-10-0-95-157.us-east-2.compute.internal                       Pending
    ...

  5. If the remaining CSRs are not approved, and are in the Pending status, approve the CSRs for your cluster machines:

    • To approve them individually, run the following command for each valid CSR:

      $ oc adm certificate approve <csr_name> 1
      1
      <csr_name> is the name of a CSR from the list of current CSRs.
    • To approve all pending CSRs, run the following command:

      $ oc get csr -o go-template='{{range .items}}{{if not .status}}{{.metadata.name}}{{"\n"}}{{end}}{{end}}' | xargs oc adm certificate approve
  6. After all client and server CSRs have been approved, the machines have the Ready status. Verify this by running the following command:

    $ oc get nodes

    Example output

    NAME      STATUS    ROLES   AGE  VERSION
    master-0  Ready     master  73m  v1.25.0
    master-1  Ready     master  73m  v1.25.0
    master-2  Ready     master  74m  v1.25.0
    worker-0  Ready     worker  11m  v1.25.0
    worker-1  Ready     worker  11m  v1.25.0

    Note

    It can take a few minutes after approval of the server CSRs for the machines to transition to the Ready status.

Additional information

Legal Notice

Copyright © 2024 Red Hat, Inc.

OpenShift documentation is licensed under the Apache License 2.0 (https://www.apache.org/licenses/LICENSE-2.0).

Modified versions must remove all Red Hat trademarks.

Portions adapted from https://github.com/kubernetes-incubator/service-catalog/ with modifications by Red Hat.

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