Chapter 5. Working with nodes

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        v1.24.0

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 using the --delete-local-data flag set to true. Local data is deleted when the node is drained:

     $ oc adm drain <node1> <node2> --delete-local-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>

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
     policy:
       name: ""
   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.

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: 2.2.0
       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

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                                          5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    00-worker                                          5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-master-container-runtime                        5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-master-kubelet                                  5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-worker-container-runtime                        5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-worker-kubelet                                  5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    99-master-generated-registries                     5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    99-master-ssh                                                                                 3.1.0             77m
    99-worker-generated-registries                     5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    99-worker-ssh                                                                                 3.1.0             77m
    rendered-master-0f314bb55448c47e6776e16e608c5912   5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             42m
    rendered-master-c7761e6162e6c9538b0cdd7eef567d38   5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m

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:
     config:
       ignition:
         version: 3.1.0
     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                                          5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    00-worker                                          5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-master-container-runtime                        5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-master-kubelet                                  5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-worker-container-runtime                        5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    01-worker-kubelet                                  5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
   
    05-worker-kernelarg-selinuxpermissive                                                         3.1.0             105s
   
    99-master-generated-registries                     5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    99-master-ssh                                                                                 3.1.0             77m
    99-worker-generated-registries                     5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m
    99-worker-ssh                                                                                 3.1.0             77m
    rendered-master-0f314bb55448c47e6776e16e608c5912   5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             42m
    rendered-master-c7761e6162e6c9538b0cdd7eef567d38   5ce9351ceb24e721e28cd82de3a44fc7cc27137c   3.1.0             65m

5. Check the nodes:

   $ oc get nodes

   Example output

   NAME                           STATUS                     ROLES    AGE   VERSION
   ip-10-0-136-161.ec2.internal   Ready                      worker   28m   v1.19.0
   ip-10-0-136-243.ec2.internal   Ready                      master   34m   v1.19.0
   ip-10-0-141-105.ec2.internal   Ready,SchedulingDisabled   worker   28m   v1.19.0
   ip-10-0-142-249.ec2.internal   Ready                      master   34m   v1.19.0
   ip-10-0-153-11.ec2.internal    Ready                      worker   28m   v1.19.0
   ip-10-0-153-150.ec2.internal   Ready                      master   34m   v1.19.0

   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.

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

Prerequisites

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

   1. View the machine config pool:

      $ oc describe machineconfigpool <name>

      For example:

      $ oc describe machineconfigpool worker

      Example output

      apiVersion: machineconfiguration.openshift.io/v1
      kind: MachineConfigPool
      metadata:
        creationTimestamp: 2019-02-08T14:52:39Z
        generation: 1
        labels:
          custom-kubelet: small-pods 1

      1

      If a label has been added it appears under labels.

   2. If the label is not present, add a key/value pair:

      $ 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:
         custom-kubelet: small-pods 2
     kubeletConfig:
       podsPerCore: 10 3
       maxPods: 250 4

   1

   Assign a name to CR.

   2

   Specify the label to apply the configuration change.

   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. 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

Procedure

1. Run:

   $ oc get Tuned/default -o yaml -n openshift-cluster-node-tuning-operator

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.

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-local-data

   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 the host:

   $ chroot /host

5. Restart the node:

   $ systemctl reboot

   In a moment, the node enters the NotReady state.

6. After the reboot is complete, mark the node as schedulable by running the following command:

   $ oc adm uncordon <node1>

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

1. A list of images currently running in at least one pod.
2. A list of images available on a host.

Prerequisites

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

   1. View the machine config pool:

      $ oc describe machineconfigpool <name>

      For example:

      $ oc describe machineconfigpool worker

      Example output

      Name:         worker
      Namespace:
      Labels:       custom-kubelet=small-pods 1

      1

      If a label has been added it appears under Labels.

   2. If the label is not present, add a key/value pair:

      $ 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:
         custom-kubelet: small-pods 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

   Selector label.

   3

   Type of eviction: evictionSoft or evictionHard.

   4

   Eviction thresholds based on a specific eviction trigger signal.

   5

   Grace periods for the soft eviction. This parameter does not apply to eviction-hard.

   6

   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

   The duration to wait before transitioning out of an eviction pressure condition.

   8

   The minimum age for an unused image before the image is removed by garbage collection.

   9

   The percent of disk usage (expressed as an integer) that triggers image garbage collection.

   10

   The percent of disk usage (expressed as an integer) that image garbage collection attempts to free.

2. Create the object:

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

   For example:

   $ oc create -f gc-container.yaml

   Example output

   kubeletconfig.machineconfiguration.openshift.io/gc-container created

3. Verify that garbage collection is active. 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

Prerequisites

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

   1. View the Machine Config Pool:

      $ oc describe machineconfigpool <name>

      For example:

      $ oc describe machineconfigpool worker

      Example output

      apiVersion: machineconfiguration.openshift.io/v1
      kind: MachineConfigPool
      metadata:
        creationTimestamp: 2019-02-08T14:52:39Z
        generation: 1
        labels:
          custom-kubelet: small-pods 1

      1

      If a label has been added it appears under labels.

   2. If the label is not present, add a key/value pair:

      $ 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:
         custom-kubelet: small-pods 2
     kubeletConfig:
       systemReserved:
         cpu: 1000m
         memory: 1Gi

   1

   Assign a name to CR.

   2

   Specify the label from the Machine Config Pool.

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