Kubernetes Common Errors

Kubernetes common errors

1. **CrashLoopBackOff**:
- **Description**: A pod repeatedly crashes and restarts.
- **Troubleshooting**:
- Check pod logs: `kubectl logs <pod-name>`.
- Describe the pod for more details: `kubectl describe pod <pod-name>`.
- Investigate the application's start-up and initialization code.

2. **ImagePullBackOff**:
- **Description**: Kubernetes cannot pull the container image from the registry.
- **Troubleshooting**:
- Verify the image name and tag.
- Check the image registry credentials.
- Ensure the image exists in the specified registry.

3. **Pending Pods**:
- **Description**: Pods remain in the "Pending" state and are not scheduled.
- Troubleshooting:
- Check node resources (CPU, memory) to ensure there is enough capacity.
- Ensure the nodes are labeled correctly if using node selectors or affinities.
- Verify there are no taints on nodes that would prevent scheduling.

4. Node Not Ready:
- Description: One or more nodes are in a "NotReady" state.
- Troubleshooting:
- Check node status: `kubectl describe node <node-name>`.
- Review kubelet logs on the affected node.
- Ensure the node has network connectivity.

5. Service Not Working
- Description: Services are not accessible or routing traffic correctly.
- Troubleshooting:
- Check the service and endpoints: `kubectl get svc` and `kubectl get endpoints`.
- Verify network policies and firewall rules.
- Ensure the pods backing the service are healthy and running.

6. **Insufficient Resources**:
- **Description**: Pods cannot be scheduled due to insufficient resources.
- **Troubleshooting**:
- Review resource requests and limits in pod specifications.
- Scale the cluster by adding more nodes.

8. **PersistentVolume Claims Pending**:
- **Description**: PVCs remain in a "Pending" state.
- **Troubleshooting**:
- Check if there are available PVs that match the PVC specifications.
- Ensure the storage class exists and is configured correctly.
- Verify that the underlying storage backend is healthy.

9. **Pod Stuck Terminating**:
- **Description**: Pods get stuck in a "Terminating" state.
- **Troubleshooting**:
- Check for finalizers that might be preventing pod deletion.
- Review the logs for shutdown hooks or long-running processes.
- Force delete the pod if necessary: `kubectl delete pod <pod-name> --force --grace-period=0`.

10. **DNS Resolution Issues**:
- **Description**: DNS lookups within the cluster fail.
- **Troubleshooting**:
- Check the DNS pod logs (e.g., CoreDNS): `kubectl logs <coredns-pod>`.
- Ensure the DNS service is running: `kubectl get svc -n kube-system`.
- Verify network policies and firewall rules do not block DNS traffic.

Reference- https://www.linkedin.com/posts/fadhel-smiti-110197242_kubernetes-common-errors-1-crashloopbackoff-activity-7217825726790602752-hf-E?utm_source=share&utm_medium=member_desktop