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I want to execute a script immediately after the container is completed successfully or terminated due to an error in the pod.

I tried by attaching handlers to Container lifecycle events like preStop but it is only called when a container is terminated due to an API request or management event such as liveness probe failure, preemption, resource contention and others.

Reference - Kubernetes Doc: https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/

Is there an alternative approach to this?

kushagra
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  • You could try to put your workload to initContainer and put your script to the main container. If you make your InitContainer script exit with code 0 even if failed, the main container starts right after the InitContainer completes. To execute it just once Job is the perfect choice. If you need to cycle the process, Deployment matches better. – VAS Jan 12 '21 at 15:07

1 Answers1

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From the official docs, as you said:

Kubernetes only sends the preStop event when a Pod is terminated. This means that the preStop hook is not invoked when the Pod is completed.

Although, the use of bare pods is not recommended. Consider using a Job Controller:

A Job creates one or more Pods and ensures that a specified number of them successfully terminate. As pods successfully complete, the Job tracks the successful completions.

You can check job conditions and wait for them with this:
kubectl wait --for=condition=complete job/your-job, then run your script. In the meanwhile add preStop event to your pods definition to run script if pods are terminated. You can write extra script which will work in the background and will be checking if job is completed and then it will run script.

while kubectl get jobs your-job -o jsonpath='{.status.conditions[? 
    (@.type=="Complete")].status}' | grep True ; do <run your main script> ; done

See more: job-completion-task.

Malgorzata
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