Mastering Kubernetes: Advanced Troubleshooting Techniques for Professionals

Kubernetes is the cornerstone of modern infrastructure, orchestrating containerized applications with efficiency and scalability. However, its complexity can make troubleshooting daunting, especially in production environments. In this guide, we’ll delve into common and advanced Kubernetes troubleshooting scenarios, providing actionable insights for DevOps, DevSecOps, and infrastructure engineers.

1. Pod Issues

a. CrashLoopBackOff Errors

Problem: Pods are continuously restarting.

Common Causes:

• Incorrect configurations or missing environment variables.

• Application crashes due to runtime errors.

• Insufficient resources (CPU/Memory).

Troubleshooting Steps:

1. Check Pod logs:

   kubectl logs <pod-name>
   

2. Inspect events:

   kubectl describe pod <pod-name>
   

3. Validate configuration:

   kubectl get pod <pod-name> -o yaml
   

   Look for errors in env, volumes, or image configurations.

4. Increase resource limits if necessary:

   resources:
     limits:
       memory: "512Mi"
       cpu: "0.5"
   

b. Pending Pods

Problem: Pods are stuck in Pending status.

Common Causes:

• Insufficient node resources.

• Unfulfilled PersistentVolumeClaims (PVCs).

• Node affinity/anti-affinity conflicts.

Troubleshooting Steps:

1. Check Pod status:

   kubectl describe pod <pod-name>
   

2. Inspect node conditions:

   kubectl describe nodes
   

3. Investigate PVC issues:

   kubectl get pvc
   

4. Adjust node affinity rules if applicable.

2. Node and Cluster Issues

a. Node NotReady State

Problem: Nodes are marked NotReady.

Common Causes:

• Kubelet or container runtime issues.

• Insufficient system resources.

• Network connectivity issues.

Troubleshooting Steps:

1. Check node status:

   kubectl describe node <node-name>
   

2. Inspect Kubelet logs:

   journalctl -u kubelet
   

3. Validate container runtime:

   systemctl status docker
   

   or

   systemctl status containerd
   

4. Check system resource usage (CPU, memory, disk):

   top
   df -h
   

b. API Server Connectivity Issues

Problem: Unable to connect to the Kubernetes API server.

Common Causes:

• API server down.

• Incorrect kubeconfig configuration.

• Networking issues (firewall, DNS).

Troubleshooting Steps:

1. Test API server endpoint:

   curl https://<api-server-url>:6443/healthz
   

2. Verify kubeconfig:

   kubectl config view
   

3. Check control plane logs:

   journalctl -u kube-apiserver
   

3. Networking Issues

a. Pods Cannot Communicate

Problem: Pods in the same namespace or across namespaces cannot communicate.

Common Causes:

• Network policies blocking traffic.

• CNI plugin misconfiguration.

• Node-to-node network issues.

Troubleshooting Steps:

1. Verify network policies:

   kubectl get networkpolicy
   

2. Test pod connectivity using ping or curl:

   kubectl exec -it <pod-name> -- curl <service-ip>
   

3. Check CNI plugin status:

   kubectl describe pod -n kube-system <cni-plugin-pod>
   

4. Validate node networking:

   ping <node-ip>
   

b. Service Unreachable

Problem: A Kubernetes service is not reachable from pods or external clients.

Common Causes:

• Incorrect service configuration.

• Endpoint issues.

• External load balancer misconfiguration.

Troubleshooting Steps:

1. Check service endpoints:

   kubectl get endpoints <service-name>
   

2. Inspect service configuration:

   kubectl describe svc <service-name>
   

3. Test service reachability:

   curl <cluster-ip>:<port>
   

4. Validate ingress or external load balancer logs.

4. Storage Issues

a. PVC Bound but Pod Cannot Mount

Problem: A PVC is successfully bound, but the pod cannot mount the volume.

Common Causes:

• Volume mount path conflict.

• Incorrect storage class configuration.

• Node compatibility issues.

Troubleshooting Steps:

1. Inspect PVC and PV status:

   kubectl get pvc
   kubectl get pv
   

2. Check pod events:

   kubectl describe pod <pod-name>
   

3. Verify storage class:

   kubectl describe storageclass <storage-class-name>
   

4. Check logs for storage provider (e.g., EBS, NFS).

b. PersistentVolume Not Released

Problem: PV remains in Released state after PVC deletion.

Common Causes:

• Retain reclaim policy.

• Orphaned volume resources.

Troubleshooting Steps:

1. Delete the PV manually if reclaim policy is Retain:

   kubectl delete pv <pv-name>
   

2. Update reclaim policy:

   persistentVolumeReclaimPolicy: Delete
   

5. Authentication and Authorization Issues

a. RBAC Authorization Failures

Problem: Users or services cannot access resources due to RBAC errors.

Common Causes:

• Missing or misconfigured role bindings.

• Incorrect service account usage.

Troubleshooting Steps:

1. Check RBAC bindings:

   kubectl get rolebinding -n <namespace>
   kubectl get clusterrolebinding
   

2. Verify permissions:

   kubectl auth can-i <verb> <resource> --as <user>
   

3. Update or create role bindings as necessary:

   apiVersion: rbac.authorization.k8s.io/v1
   kind: RoleBinding
   metadata:
     name: example-rolebinding
   roleRef:
     apiGroup: rbac.authorization.k8s.io
     kind: Role
     name: example-role
   subjects:
   - kind: User
     name: example-user
   

b. Service Account Token Issues

Problem: Pods fail to authenticate with the Kubernetes API.

Common Causes:

• Expired service account tokens.

• Missing service account configurations.

Troubleshooting Steps:

1. Check service account:

   kubectl get sa -n <namespace>
   

2. Verify token mounts:

   kubectl describe pod <pod-name> | grep token
   

3. Regenerate service account tokens if necessary.

Final Thoughts

Kubernetes troubleshooting requires a methodical approach, combining a deep understanding of cluster internals with real-world debugging experience. By mastering these advanced techniques, you’ll ensure smoother operations, reduced downtime, and enhanced reliability in your Kubernetes environment.

What’s the most challenging Kubernetes issue you’ve faced? Share your experience in the comments!