How to fix FailedPostStartHook in Kubernetes

KubernetesINTERMEDIATEMEDIUM

PostStartHookError occurs when a container lifecycle postStart hook fails. The hook failure kills the container, causing restart loops. Fix the hook command or remove it.

What this error means

PostStartHookError (FailedPostStartHook) occurs when a container's postStart lifecycle hook fails to execute successfully. PostStart hooks run immediately after a container is created, and any failure causes Kubernetes to kill the container. This creates a challenging situation: the container starts, the hook runs and fails, the container is killed, and the cycle repeats. The pod may appear stuck in ContainerCreating or enter a restart loop depending on timing.

Typical symptoms

How to fix "FailedPostStartHook"

1Check pod events for hook failure

Inspect pod events:

bash

kubectl describe pod <pod-name>

Look for:
- FailedPostStartHook events
- Specific error messages (may be empty in newer K8s versions)

Also check:

bash

kubectl get events --field-selector involvedObject.name=<pod-name>

2Test the hook command manually

Remove the hook temporarily and test in the running container:

yaml

# Comment out the lifecycle hook
# lifecycle:
#   postStart:
#     exec:
#       command: ["/scripts/init.sh"]

Then exec in and test:

bash

kubectl exec -it <pod-name> -- /bin/sh
/scripts/init.sh
echo $?  # Check exit code

3Verify hook command exists and is executable

Common issues:

yaml

# Wrong - command doesn't exist
lifecycle:
  postStart:
    exec:
      command: ["/nonexistent/script.sh"]

# Wrong - no execute permission
lifecycle:
  postStart:
    exec:
      command: ["/scripts/init.sh"]  # Missing chmod +x

# Correct
lifecycle:
  postStart:
    exec:
      command: ["/bin/sh", "-c", "chmod +x /scripts/init.sh && /scripts/init.sh"]

4Redirect hook output for debugging

PostStart hooks don't automatically log to kubectl logs. Redirect output:

yaml

lifecycle:
  postStart:
    exec:
      command:
      - /bin/sh
      - -c
      - |
        /scripts/init.sh > /proc/1/fd/1 2>&1

This sends hook output to the container's stdout where kubectl logs can capture it.

5Handle timing issues

If the hook connects to services not yet ready:

yaml

lifecycle:
  postStart:
    exec:
      command:
      - /bin/sh
      - -c
      - |
        sleep 5  # Wait for container to stabilize
        curl -f http://localhost:8080/ready || exit 0  # Don't fail if not ready

Consider whether the logic belongs in the application startup instead of a hook.

6Use HTTP GET for simpler hooks

For calling endpoints, HTTP hooks can be cleaner:

yaml

lifecycle:
  postStart:
    httpGet:
      path: /initialize
      port: 8080
      scheme: HTTP

Note: HTTP GET hooks also fail if the endpoint returns non-2xx status, so ensure your endpoint is ready immediately on container start.

How to fix FailedPostStartHook in Kubernetes

What this error means

Typical symptoms

Common causes

How to fix "FailedPostStartHook"

Advanced notes

Related errors

Official resources & further reading