Debugging Kubernetes issues can often be challenging due to the complexity of the environment. Below, I’ve outlined some of the most common Kubernetes-related errors and step-by-step methods to debug them.

1. Pod Stuck in Pending State
Cause: This usually happens due to insufficient resources, scheduling issues, or lack of network connectivity.

How to Debug:

Check Pod Events: Run kubectl describe pod -n and look for events at the bottom to identify scheduling issues.
Check Node Status: Use kubectl get nodes to ensure nodes are Ready.
Check Resource Requests: Verify resource requests and limits in the Pod spec. Insufficient resources can prevent scheduling.
Inspect Network Policies: Check if any Network Policies are blocking connectivity.
Fix: Adjust resource requests, check node availability, and ensure proper network connectivity.

2. CrashLoopBackOff Error

Cause: The container repeatedly fails and restarts due to misconfiguration, application errors, or insufficient resources.

How to Debug:

Inspect Logs: Use kubectl logs <pod-name> -n <namespace> --previous to see logs from the last failed attempt.
Describe the Pod: Use kubectl describe pod <pod-name> -n <namespace> to see if there are OOMKilled or other error events.
Check Resource Limits: Ensure the container has enough CPU/memory.
Look at Container Command/Arguments: Misconfigured startup commands can cause failures.
Fix: Correct application errors, adjust resource limits, or modify startup commands.

3. ImagePullBackOff / ErrImagePull

Cause: Kubernetes is unable to pull the specified image, usually due to incorrect image name, tag, or lack of permissions.

How to Debug:

Describe the Pod: kubectl describe pod <pod-name> -n <namespace> to see detailed error messages regarding image pull failures.
Check Image Name and Tag: Ensure the image exists in the specified registry.
Check Registry Credentials: If pulling from a private registry, make sure the correct credentials are configured (imagePullSecrets).
Fix: Correct the image name, tag, or registry credentials.

4. Node Not Ready

Cause: Node is in NotReady state due to networking issues, disk pressure, memory pressure, or kubelet problems.

How to Debug:

Check Node Events: kubectl describe node <node-name> to see events related to node health.
Inspect Node Status: Use kubectl get nodes -o wide to check node conditions.
Check Kubelet Logs: SSH into the node and check kubelet logs with journalctl -u kubelet for more detailed errors.
Fix: Resolve disk/memory pressure, ensure network connectivity, and check if the kubelet is running correctly.

5. Service Not Accessible / Pending

Cause: Service is not reachable, or LoadBalancer service remains in Pending due to lack of external IP provisioning.

How to Debug:

Describe the Service: Use kubectl describe svc <service-name> -n <namespace> to see details about the service.
Check Endpoints: kubectl get endpoints <service-name> -n <namespace> should show the IP addresses of connected pods.
Network Issues: Verify network configuration and check for Network Policies that might block traffic.
Check Cloud Provider: For LoadBalancer, ensure that your cloud provider’s resources (like Load Balancers) are available.
Fix: Correct network configurations, ensure the cloud provider can provision resources, or switch to a different service type.

6. PVC Pending / Volume Mount Errors

Cause: PersistentVolumeClaim (PVC) cannot be bound to a PersistentVolume (PV), or there are permission issues with mounted volumes.

How to Debug:

Describe the PVC: kubectl describe pvc <pvc-name> -n <namespace> to see why it's not binding.
Check StorageClass: Ensure the StorageClass is correctly defined and available.
Inspect Pod Events: Look for permission errors in kubectl describe pod <pod-name> -n <namespace>.
Fix: Adjust StorageClass parameters, ensure sufficient storage resources, and correct volume mount paths.

7. High Latency / Performance Issues

Cause: Cluster performance issues due to resource bottlenecks, network problems, or unoptimized application deployments.

How to Debug:

Check Resource Usage: Use kubectl top nodes and kubectl top pods to see CPU and memory usage.
Check Network Performance: Use tools like kubectl exec with network testing commands (ping, curl) to verify connectivity.
Inspect Logs: Analyze application logs and system logs for any performance-related errors.
Fix: Scale resources, optimize application deployments, and troubleshoot any specific network performance issues.

8. Unauthorized Access / RBAC Denied

Cause: Insufficient permissions due to misconfigured Role-Based Access Control (RBAC).

How to Debug:

Check Role Bindings: Use kubectl get rolebinding,clusterrolebinding -n <namespace> to inspect RBAC bindings.
Describe the Resource: kubectl describe <resource> will show RBAC-related errors.
Audit Logs: Check audit logs for denied actions.
Fix: Update RBAC policies to grant necessary permissions.

9. Certificate Errors in API Server or Ingress

Cause: SSL certificate errors often due to expired certificates, misconfigurations, or missing certificate authorities.

How to Debug:

Inspect Certificate Expiry: Use openssl s_client -connect <service>:443 to view certificate details.
Check Ingress Logs: Analyze logs of the Ingress controller to see SSL handshake errors.
Describe Ingress: kubectl describe ingress <ingress-name> -n <namespace> to identify misconfigurations.
Fix: Update certificates, adjust Ingress TLS configurations, and ensure CA certificates are correctly configured.

10. DNS Resolution Issues

Cause: Pod-to-Pod or Pod-to-Service DNS issues caused by CoreDNS errors or network misconfigurations.

How to Debug:

Check DNS Logs: Use kubectl logs <coredns-pod-name> -n kube-system to see DNS errors.
Test DNS Resolution: Use kubectl exec <pod-name> -- nslookup <service-name> to test DNS resolution inside the cluster.
Inspect Network Policies: Ensure that policies are not blocking DNS traffic.
Fix: Restart CoreDNS pods, adjust network policies, or increase CoreDNS resources.

Summary

When dealing with Kubernetes errors, always start by describing the resource (kubectl describe) and reviewing the logs (kubectl logs). These provide the most immediate insight into the root cause of the problem. If you encounter persistent issues, consider checking node-level logs or the control plane for broader cluster-level problems.