How to make Cluster Autoscaler skip a node for scale down in OpenShift 4

Environment

• Red Hat OpenShift Container Platform (RHOCP)
  • 4

Issue

• Can I configure Cluster Autoscaler to skip a node for scale down process where a specific pod is running in OCP 4?
• How to stop the Cluster Autoscaler from evicting a specific pod in the scale-down process?

Resolution

To make the cluster autoscaler skip a node for scale-down process, add the annotation "cluster-autoscaler.kubernetes.io/safe-to-evict": "false" in the deployment or the pod definition. Example:

[...]
template:
     metadata:
       labels:
         app: jenkins
       annotations:
         "cluster-autoscaler.kubernetes.io/safe-to-evict": "false"             ## <-----

     spec:
       nodeSelector:
         failure-domain.beta.kubernetes.io/zone: us-west-2b
[...]

Root Cause

Cluster Autoscaler is designed to reduce the number of nodes when the load is reduced. In this process, Cluster Autoscaler can delete any node which satisfies the criteria. Refer to How does scale down works in Cluster Autoscaler in OCP 4? for additional information.

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