CKAD — Common Pod Problems
CrashLoopBackOff
The container keeps crashing and Kubernetes keeps restarting it with increasing backoff delays.
# Check the exit code
kubectl describe pod my-pod | grep -A3 "Last State"
# Exit Code: 1 → Application error
# Exit Code: 137 → OOMKilled (out of memory)
# Exit Code: 139 → Segfault
# Check the logs
kubectl logs my-pod --previous
# Common fixes:
# - Wrong command/args in the Pod spec
# - Missing environment variables or config
# - Application bug
# - Insufficient memory (increase limits)
Exit code reference:
- 0 — Normal exit (success)
- 1 — Application error
- 137 — OOMKilled (SIGKILL) — container exceeded memory limits
- 139 — Segmentation fault (SIGSEGV)
- 143 — Graceful termination (SIGTERM)
ImagePullBackOff
Kubernetes cannot download the container image.
kubectl describe pod my-pod | grep -A5 Events
# "Failed to pull image" or "image not found"
# Common fixes:
# - Check image name and tag
# - Verify the image exists in the registry
# - Add imagePullSecrets for private registries
# - Check network connectivity from nodes
Pending Pod
The Pod cannot be scheduled to any node.
kubectl describe pod my-pod | grep -A5 Events
# "Insufficient cpu" → No node has enough CPU
# "Insufficient memory" → No node has enough memory
# "no nodes available" → All nodes are tainted or cordoned
# "pod has unbound immediate PersistentVolumeClaims" → PVC not bound
# Common fixes:
# - Reduce resource requests
# - Add more nodes
# - Check node taints: kubectl describe node <name> | grep Taint
# - Check PVC: kubectl get pvc
OOMKilled
The container used more memory than its limit allows. Kubernetes kills it immediately.
kubectl describe pod my-pod | grep OOMKilled
# Fix: Increase the memory limit
kubectl set resources deployment/web -c app --limits=memory=512Mi
Quick Reference: Status → Action
| Status | First Command | Likely Cause |
|---|---|---|
| CrashLoopBackOff | kubectl logs --previous |
App error, wrong cmd, missing config |
| ImagePullBackOff | kubectl describe pod |
Wrong image name, private registry |
| Pending | kubectl describe pod |
No resources, taints, PVC issues |
| OOMKilled | kubectl describe pod |
Memory limit too low |
| RunContainerError | kubectl describe pod |
Wrong command, missing binary |
Next: kubectl debug
