The FailedPostStartHook error occurs when a container's postStart lifecycle hook fails to execute successfully, preventing the container from starting properly.
The FailedPostStartHook event indicates that your container's postStart lifecycle hook exited with a non-zero status or failed to complete. PostStart hooks run immediately after a container is created (simultaneously with the container's ENTRYPOINT) and are used for initialization logic. When this hook fails, Kubernetes broadcasts a FailedPostStartHook event and typically restarts the container, preventing it from transitioning to a Running state. This creates a restart loop where the container keeps trying to start but fails at the postStart hook phase. The hook failure is often silent from a logging perspective—errors don't appear in container logs (kubectl logs) because the hook runs outside the normal container logging path. You must check pod events or kubelet logs to see what went wrong.
View the pod events to see the FailedPostStartHook message:
kubectl describe pod <pod-name>Look for events like:
Warning FailedPostStartHook Container hook failed: command 'xxx' exited with 1Remove or comment out the postStart hook in your pod spec to confirm the container itself can start:
lifecycle:
# postStart:
# exec:
# command: ["/bin/sh", "-c", "your-command"]If the container starts successfully without the hook, the issue is definitely in the hook configuration.
Start the container without the hook, then exec into it to test the command:
kubectl exec -it <pod-name> -- /bin/sh
# Run your postStart command manually
/path/to/your/script.sh
echo $? # Check exit codeFor scripts mounted from ConfigMaps, invoke through a shell:
lifecycle:
postStart:
exec:
command: ["/bin/sh", "-c", "sh /scripts/init.sh"]Ensure the script uses absolute paths and the shell exists in your container image.
If your hook needs network access, add a delay since CNI may not be ready:
lifecycle:
postStart:
exec:
command: ["/bin/sh", "-c", "sleep 5 && curl http://service/register"]If your postStart hook takes time, ensure liveness probes don't kill the container before the hook completes:
livenessProbe:
initialDelaySeconds: 30 # Wait for postStart to complete
failureThreshold: 3PostStart hooks run asynchronously with the container's ENTRYPOINT—there's no guarantee which completes first. If your application depends on hook completion before starting, you need coordination mechanisms.
For debugging, check kubelet logs on the node since postStart failures don't appear in container logs:
journalctl -u kubelet | grep -i poststartIf the hook produces exit code 137, it was killed by OOM or Kubernetes before completion. Consider whether a postStart hook is the right approach—for complex initialization, an init container might be more appropriate and easier to debug.
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