Red Hat OpenShift Container Platform

Configure a priority expander for the cluster autoscaler

Configure a priority expander to control which machine set expands when the cluster autoscaler increases the size of the cluster. You can create a priority expander config map by listing priority values and regular expressions that define machine sets.

Prerequisites

You have deployed an Red Hat OpenShift Container Platform cluster that uses the Machine API.
You have access to the cluster using an account with cluster-admin permissions.
You have installed the OpenShift CLI (oc).

Procedure

List the compute machine sets on your cluster by running the following command:

$ oc get machinesets.machine.openshift.io

Example output

NAME                                        DESIRED   CURRENT   READY   AVAILABLE   AGE
archive-agl030519-vplxk-worker-us-east-1c   1         1         1       1           25m
fast-01-agl030519-vplxk-worker-us-east-1a   1         1         1       1           55m
fast-02-agl030519-vplxk-worker-us-east-1a   1         1         1       1           55m
fast-03-agl030519-vplxk-worker-us-east-1b   1         1         1       1           55m
fast-04-agl030519-vplxk-worker-us-east-1b   1         1         1       1           55m
prod-01-agl030519-vplxk-worker-us-east-1a   1         1         1       1           33m
prod-02-agl030519-vplxk-worker-us-east-1c   1         1         1       1           33m

Using regular expressions, construct one or more patterns that match the name of any compute machine set that you want to set a priority level for.

For example, use the regular expression pattern *fast* to match any compute machine set that includes the string fast in its name.
Create a cluster-autoscaler-priority-expander.yml YAML file that defines a config map similar to the following:
apiVersion: v1 kind: ConfigMap metadata: name: cluster-autoscaler-priority-expander namespace: openshift-machine-api data: priorities: |- 10: - .*fast.* - .*archive.* 40: - .*prod.*
Define the priority of your machine sets. The priorities values must be positive integers. The cluster autoscaler uses higher-value priorities before lower-value priorities. For each priority level, specify the regular expressions that correspond to the machine sets you want to use.

Create the config map by running the following command:

$ oc create configmap cluster-autoscaler-priority-expander \
  --from-file=<location_of_config_map_file>/cluster-autoscaler-priority-expander.yml

Verification

Review the config map by running the following command:

$ oc get configmaps cluster-autoscaler-priority-expander -o yaml

Next steps

To use the priority expander, ensure that the ClusterAutoscaler resource definition is configured to use the expanders: ["Priority"] parameter.