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Chapter 1. Scheduling logging resources

You can schedule logging resources by defining node selectors, taints and tolerations, and affinity and anti-affinity configurations.

Node selector
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 pair as the label on the node.
Taints and toleration
Taints and tolerations control which pods should, or should not, be scheduled on nodes.
Affinity and anti-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.
Important

If you configure both nodeSelector and `nodeAffinity`fields, the conditions of both fields must be met for the pod to be scheduled onto a candidate node.

1.1. Using tolerations to control log collector pod placement
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By default, log collector pods have the following tolerations configuration: 

apiVersion: v1
kind: Pod
metadata:
  name: collector-example
  namespace: openshift-logging
spec:
# ...
  collection:
    type: vector
    tolerations:
    - effect: NoSchedule
      key: node-role.kubernetes.io/master
      operator: Exists
    - effect: NoSchedule
      key: node.kubernetes.io/disk-pressure
      operator: Exists
    - effect: NoExecute
      key: node.kubernetes.io/not-ready
      operator: Exists
    - effect: NoExecute
      key: node.kubernetes.io/unreachable
      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
# ...

Prerequisites

  • You have installed the Red Hat OpenShift Logging Operator and OpenShift CLI (oc).

Procedure

  1. Add a taint to a node where you want logging collector pods to schedule logging collector pods by running the following command: 

    $ oc adm taint nodes <node_name> <key>=<value>:<effect>

    Example command

    $ oc adm taint nodes node1 collector=node:NoExecute

    This example places a taint on node1 that has key collector, value node, and taint effect NoExecute. You must use the NoExecute taint effect. NoExecute schedules only pods that match the taint and removes existing pods that do not match.

  2. Edit the collection stanza of the ClusterLogging custom resource (CR) to configure a toleration for the logging collector pods: 

    apiVersion: logging.openshift.io/v1
kind: ClusterLogging
metadata:
# ...
spec:
# ...
  collection:
    type: vector
    tolerations:
    - key: collector
    1 
    
      operator: Exists
    2 
    
      effect: NoExecute
    3 
    
      tolerationSeconds: 6000
    4 
    
    resources:
      limits:
        memory: 2Gi
      requests:
        cpu: 100m
        memory: 1Gi
# ...
    1
    Specify the key that you added to the node.
    2
    Specify the Exists operator to require the key/value/effect parameters to match.
    3
    Specify the NoExecute effect.
    4
    Optionally, specify the tolerationSeconds parameter to set how long a pod can remain bound to a node before being evicted.

This toleration matches the taint created by the oc adm taint command. A pod with this toleration can be scheduled onto node1.

1.2. Configuring resources and scheduling for logging collectors
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Administrators can modify the resources and scheduling of the collector by configuring the collector field in a ClusterLogForwarder custom resource (CR).

Prerequisites

  • You have administrator permissions.
  • You have installed Red Hat OpenShift Logging Operator.
  • You have created a ClusterLogForwarder CR.

Procedure

  1. Update the ClusterLogForwarder CR:

    Example ClusterLogForwarder CR YAML

    apiVersion:  observability.openshift.io/v1
kind: ClusterLogForwarder
metadata:
  name: <name>
  namespace: <namespace>
spec:
  collector:
    nodeSelector:
      collector: needed
    resources:
      limits:
        memory: 1Gi
      requests:
        cpu: 100m
        memory: 1Gi
    tolerations:
    - key: "logging"
      operator: "Exists"
      effect: "NoExecute"
      tolerationSeconds: 6000
    affinity:
      nodeAffinity:
        preferredDuringSchedulingIgnoredDuringExecution:
        - preference:
            matchExpressions:
            - key: label-1
              operator: Exists
          weight: 1
      podAffinity:
        preferredDuringSchedulingIgnoredDuringExecution:
        - podAffinityTerm:
            labelSelector:
              matchExpressions:
              - key: test
                operator: In
                values:
                 - value1
            topologyKey: kubernetes.io/hostname
          weight: 50
        requiredDuringSchedulingIgnoredDuringExecution:
        - labelSelector:
            matchExpressions:
            - key: run
              operator: In
              values:
              - test
          namespaceSelector: {}
          topologyKey: kubernetes.io/hostname
      podAntiAffinity:
        preferredDuringSchedulingIgnoredDuringExecution:
        - podAffinityTerm:
           labelSelector:
             matchExpressions:
             - key: security
               operator: In
               values:
               - S2
           topologyKey: topology.kubernetes.io/zone
          weight: 100
# ...

  2. Apply the ClusterLogForwarder CR by running the following command: 

    $ oc apply -f <filename>.yaml

1.3. Viewing logging collector pods
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You can view the logging collector pods and the corresponding nodes that they are running on.

Procedure

  • Run the following command in a project to view the logging collector pods and their details: 

    $ oc get pods --selector component=collector -o wide -n <project_name>

    Example output

    NAME           READY  STATUS    RESTARTS   AGE     IP            NODE                  NOMINATED NODE   READINESS GATES
collector-8d69v  1/1    Running   0          134m    10.130.2.30   master1.example.com   <none>           <none>
collector-bd225  1/1    Running   0          134m    10.131.1.11   master2.example.com   <none>           <none>
collector-cvrzs  1/1    Running   0          134m    10.130.0.21   master3.example.com   <none>           <none>
collector-gpqg2  1/1    Running   0          134m    10.128.2.27   worker1.example.com   <none>           <none>
collector-l9j7j  1/1    Running   0          134m    10.129.2.31   worker2.example.com   <none>           <none>

1.4. Loki pod placement
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You can control which nodes the Loki pods run on, and prevent other workloads from using those nodes, by using tolerations or node selectors on the pods.

You can apply tolerations to the log store pods with the LokiStack custom resource (CR) and apply taints to a node with the node specification. A taint on a node is a key:value pair that instructs the node to repel all pods that do not allow the taint. Using a specific key:value pair that is not on other pods ensures that only the log store pods can run on that node.

Example LokiStack with node selectors

apiVersion: loki.grafana.com/v1
kind: LokiStack
metadata:
  name: logging-loki
  namespace: openshift-logging
spec:
# ...
  template:
    compactor:
1 

      nodeSelector:
        node-role.kubernetes.io/infra: ""
2 

    distributor:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    gateway:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    indexGateway:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    ingester:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    querier:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    queryFrontend:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
    ruler:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
# ...

1
Specifies the component pod type that applies to the node selector.
2
Specifies the pods that are moved to nodes containing the defined label.

In the previous example configuration, all Loki pods are moved to nodes containing the node-role.kubernetes.io/infra: "" label.

Example LokiStack CR with node selectors and tolerations

apiVersion: loki.grafana.com/v1
kind: LokiStack
metadata:
  name: logging-loki
  namespace: openshift-logging
spec:
# ...
  template:
    compactor:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    distributor:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    indexGateway:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    ingester:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    querier:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    queryFrontend:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    ruler:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
    gateway:
      nodeSelector:
        node-role.kubernetes.io/infra: ""
      tolerations:
      - effect: NoSchedule
        key: node-role.kubernetes.io/infra
        value: reserved
      - effect: NoExecute
        key: node-role.kubernetes.io/infra
        value: reserved
# ...

To configure the nodeSelector and tolerations fields of the LokiStack (CR), you can use the oc explain command to view the description and fields for a particular resource: 

$ oc explain lokistack.spec.template

Example output

KIND:     LokiStack
VERSION:  loki.grafana.com/v1

RESOURCE: template <Object>

DESCRIPTION:
     Template defines the resource/limits/tolerations/nodeselectors per
     component

FIELDS:
   compactor	<Object>
     Compactor defines the compaction component spec.

   distributor	<Object>
     Distributor defines the distributor component spec.
...

For more detailed information, you can add a specific field: 

$ oc explain lokistack.spec.template.compactor

Example output

KIND:     LokiStack
VERSION:  loki.grafana.com/v1

RESOURCE: compactor <Object>

DESCRIPTION:
     Compactor defines the compaction component spec.

FIELDS:
   nodeSelector	<map[string]string>
     NodeSelector defines the labels required by a node to schedule the
     component onto it.
...

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