4장. Configuring MCO-related custom resources

Prerequisites

1. Obtain the label associated with the static MachineConfigPool CR 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: set-kubelet-config 

      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=set-kubelet-config

Procedure

1. View the available machine configuration objects that you can select:

   $ oc get machineconfig

   By default, the two kubelet-related configs are 01-master-kubelet and 01-worker-kubelet.

2. Check the current value for the maximum pods per node:

   $ oc describe node <node_name>

   For example:

   $ oc describe node ci-ln-5grqprb-f76d1-ncnqq-worker-a-mdv94

   Look for value: pods: <value> in the Allocatable stanza:

   Example output

   Allocatable:
    attachable-volumes-aws-ebs:  25
    cpu:                         3500m
    hugepages-1Gi:               0
    hugepages-2Mi:               0
    memory:                      15341844Ki
    pods:                        250

3. Configure the worker nodes as needed:

   1. Create a YAML file similar to the following that contains the kubelet configuration:

      중요

      Kubelet configurations that target a specific machine config pool also affect any dependent pools. For example, creating a kubelet configuration for the pool containing worker nodes will also apply to any subset pools, including the pool containing infrastructure nodes. To avoid this, you must create a new machine config pool with a selection expression that only includes worker nodes, and have your kubelet configuration target this new pool.

      apiVersion: machineconfiguration.openshift.io/v1
      kind: KubeletConfig
      metadata:
        name: set-kubelet-config
      spec:
        machineConfigPoolSelector:
          matchLabels:
            custom-kubelet: set-kubelet-config 

      1

      
        kubeletConfig: 

      2

      
            podPidsLimit: 8192
            containerLogMaxSize: 50Mi
            maxPods: 500

      1

      Enter the label from the machine config pool.

      2

      Add the kubelet configuration. For example:

      • Use podPidsLimit to set the maximum number of PIDs in any pod.
      • Use containerLogMaxSize to set the maximum size of the container log file before it is rotated.

      • Use maxPods to set the maximum pods per node.

        참고

        The rate at which the kubelet talks to the API server depends on queries per second (QPS) and burst values. The default values, 50 for kubeAPIQPS and 100 for kubeAPIBurst, are sufficient if there are limited pods running on each node. It is recommended to update the kubelet QPS and burst rates if there are enough CPU and memory resources on the node.

        apiVersion: machineconfiguration.openshift.io/v1
        kind: KubeletConfig
        metadata:
          name: set-kubelet-config
        spec:
          machineConfigPoolSelector:
            matchLabels:
              custom-kubelet: set-kubelet-config
          kubeletConfig:
            maxPods: <pod_count>
            kubeAPIBurst: <burst_rate>
            kubeAPIQPS: <QPS>

   2. Update the machine config pool for workers with the label:

      $ oc label machineconfigpool worker custom-kubelet=set-kubelet-config

   3. Create the KubeletConfig object:

      $ oc create -f change-maxPods-cr.yaml

Verification

1. Verify that the KubeletConfig object is created:

   $ oc get kubeletconfig

   Example output

   NAME                      AGE
   set-kubelet-config        15m

   Depending on the number of worker nodes in the cluster, wait for the worker nodes to be rebooted one by one. For a cluster with 3 worker nodes, this could take about 10 to 15 minutes.

2. Verify that the changes are applied to the node:

   1. Check on a worker node that the maxPods value changed:

      $ oc describe node <node_name>

   2. Locate the Allocatable stanza:

       ...
      Allocatable:
        attachable-volumes-gce-pd:  127
        cpu:                        3500m
        ephemeral-storage:          123201474766
        hugepages-1Gi:              0
        hugepages-2Mi:              0
        memory:                     14225400Ki
        pods:                       500 

      1

      
       ...

      1

      In this example, the pods parameter should report the value you set in the KubeletConfig object.

3. Verify the change in the KubeletConfig object:

   $ oc get kubeletconfigs set-kubelet-config -o yaml

   This should show a status of True and type:Success, as shown in the following example:

   spec:
     kubeletConfig:
       containerLogMaxSize: 50Mi
       maxPods: 500
       podPidsLimit: 8192
     machineConfigPoolSelector:
       matchLabels:
         custom-kubelet: set-kubelet-config
   status:
     conditions:
     - lastTransitionTime: "2021-06-30T17:04:07Z"
       message: Success
       status: "True"
       type: Success