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kuberneteskind

How to evict pods in kubernetes?

I'm testing a trigger i set on my k8s cluster. What it does it that detects if a pod is evicted. So to test I ran

kubectl drain <NODENAME> --ignore-daemonsets --force

but the evicted pods are just automatically deleted instead of staying in cluster. Can you guys help me on how can I evict a pod? I'm using kind to test this locally on my computer. Actually I want to read the evicted pod yaml after its evicted so that I can build that trigger.

Solution

  • First, to answer the title question: "How to evict pods in kubernetes?" There are a number of additional ways to trigger pod eviction, but two easy ones:

    API Based Eviction

    There is an API you can use to evict a pod manually. To use the API:

    Apply a NoExecute Taint

    A NoExecute taint that your pod does not tolerate will cause it to be evicted.

    kubectl taint nodes node1 key1=value1:NoExecute

    Now, the text of your question asks a slightly different question: reading the pod resource after a successful eviction. At least in my environment and k8s version, as soon as a pod is evicted, it is deleted by the service account associated with the node it was running on.

    In practice, many things can delete pods - including garbage collectors, so querying a pod after it has been terminated is fraught with potential race conditions.

    Instead, I would recommend setting up a programmatic watch for pod events. client-go offers the Informer pattern to accomplish this with a bit of boilerplate.

    Create an informer for Pods, define an UpdateFunc for your event handler, and you will reliably receive pod state changes as they are processed by the API -- which you can then assess to determine if they were evicted.