Apply the following best practices to scale the number of worker machines in your OpenShift Container Platform cluster. You scale the worker machines by increasing or decreasing the number of replicas that are defined in the worker MachineSet.

When scaling up the cluster to higher node counts:

  • Spread nodes across all of the available zones for higher availability.

  • Scale up by no more than 25 to 50 machines at once.

  • Consider creating new MachineSets in each available zone with alternative instance types of similar size to help mitigate any periodic provider capacity constraints. For example, on AWS, use m5.large and m5d.large.

Cloud providers might implement a quota for API services. Therefore, gradually scale the cluster.

The controller might not be able to create the machines if the replicas in the MachineSets are set to higher numbers all at one time. The number of requests the cloud platform, which OpenShift Container Platform is deployed on top of, is able to handle impacts the process. The controller will start to query more while trying to create, check, and update the machines with the status. The cloud platform on which OpenShift Container Platform is deployed has API request limits and excessive queries might lead to machine creation failures due to cloud platform limitations.

Modifying a MachineSet

To make changes to a MachineSet, edit the MachineSet YAML. Then, remove all machines associated with the MachineSet by deleting each machine 'or scaling down the MachineSet to 0 replicas. Then, scale the replicas back to the desired number. Changes you make to a MachineSet do not affect existing machines.

If you need to scale a MachineSet without making other changes, you do not need to delete the machines.

By default, the OpenShift Container Platform router pods are deployed on workers. Because the router is required to access some cluster resources, including the web console, do not scale the worker MachineSet to 0 unless you first relocate the router pods.

Prerequisites
  • Install an OpenShift Container Platform cluster and the oc command line.

  • Log in to oc as a user with cluster-admin permission.

Procedure
  1. Edit the MachineSet:

    $ oc edit machineset <machineset> -n openshift-machine-api
  2. Scale down the MachineSet to 0:

    $ oc scale --replicas=0 machineset <machineset> -n openshift-machine-api

    Or:

    $ oc edit machineset <machineset> -n openshift-machine-api

    Wait for the machines to be removed.

  3. Scale up the MachineSet 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 new Machines contain changes you made to the Machineset.