Determining that a Job failure was due to image pull errors in Kubernetes

When creating a kubernetes Job, it can fail for several different reasons, one of which is that the associated container image cannot be successfully pulled from the registry. However, after the job has completed I can't figure out a way to definitively determine that the failure was due to an image pull failure rather than some other err that caused the deadline to be exceeded.

Consider the case where I create a job similar to the following YAML:

kind: Job
apiVersion: batch/v1
metadata:
  name: test-job-image-pull
  namespace: mynamespace
spec:
  completions: 1
  activeDeadlineSeconds: 300
  template:
    spec:
      restartPolicy: Never
      containers:
        - name: mycontainer
          command:
            - mycommand
          imagePullPolicy: IfNotPresent
          image: 'my/nonexistentcontainer:latest'

When starting the job, it will create the pod and try to pull the my/nonexistentconatiner:latest image, which will fail. While the pod is attempting to pull the image, I can check the pod status and will notice that the container status is in waiting state with reason ErrImagePull. But after the deadline is exceeded, the job will fail and the pod will be automatically deleted, so I can no longer retrieve any information about the pod failure from the pod itself. The Job itself will have a status like the following:

status:
  conditions:
    - type: Failed
      status: 'True'
      lastProbeTime: '2024-07-30T15:49:01Z'
      lastTransitionTime: '2024-07-30T15:49:01Z'
      reason: DeadlineExceeded
      message: Job was active longer than specified deadline
  startTime: '2024-07-30T15:48:31Z'
  failed: 1
  uncountedTerminatedPods: {}
  ready: 0

So I can see that the job failed because of DeadlineExceeded, but I can no longer definitively determine that the failure was due to an image pull error. Is there a way to get kubernetes to keep the pod around for inspection when image pull fails? Or another way to definitively determine the cause of failure?

Solution

But after the deadline is exceeded, the job will fail and the pod will be automatically deleted

This part is key to the example you provided. Kubernetes jobs will delete any active pods when it fails. Any pods that are still stuck trying to pull the container image are considered active and will be cleaned up. I think this aspect might be by design of Kubernetes, as the job needs a way to ensure pods do not go into an endless restart loop (as it may have a restart policy of its own).

I think your best bet is to set up a logging system in your cluster so that you have a persistent store of your logs for debugging. Pod logs are temporary unless stored somewhere. This is recommended especially when the cause of failure is unknown.