Mastering Troubleshooting: Common Issues in Azure Kubernetes Service (AKS) Clusters and How to Resolve Them

Managing an Azure Kubernetes Service (AKS) cluster can offer powerful benefits for deploying and scaling containerized applications. However, like any complex system, AKS can encounter issues that impact performance, availability, or functionality. Being able to quickly identify and troubleshoot these problems is essential for maintaining a healthy cluster.

In this guide, we will explore some of the most common AKS issues, their causes, and practical steps to resolve them. Whether you're a DevOps engineer or a developer managing AKS, this article aims to provide clear, actionable insights.

1. Diagnosing Cluster Connectivity Issues

Symptoms:

• Unable to access the Kubernetes dashboard or APIs.
• kubectl commands fail or timeout.

Troubleshooting Steps:

• Check Cluster Status:
  • Use Azure CLI: az aks show --resource-group <resource-group> --name <cluster-name>
  • Verify that the cluster is in a "Succeeded" state.
• Validate kubeconfig:
  • Ensure your kubeconfig is configured correctly: az aks get-credentials --resource-group <resource-group> --name <cluster-name>
  • Confirm current context: kubectl config current-context
• Network Security Groups (NSGs):
  • Check if NSGs or firewalls are blocking access to the cluster API server.
• Azure Firewall and VPNs:
  • Ensure network routes and firewalls permit traffic to the AKS API endpoint.

2. Pod Crashes or Not Starting

Symptoms:

• Pods stay in Pending or CrashLoopBackOff states.

Troubleshooting Steps:

• Check Pod Status:
  • kubectl get pods --namespace <namespace>
  • Identify problematic pods.
• Describe Pod:
  • kubectl describe pod <pod-name> --namespace <namespace>
  • Look for events indicating scheduling issues, image pull errors, or resource constraints.
• Inspect Logs:
  • kubectl logs <pod-name> --namespace <namespace>
  • Review application logs for errors.
• Resource Limits and Quotas:
  • Verify if the node has enough CPU/memory.
  • Check namespace resource quotas.
• Image Issues:
  • Confirm image tags are correct and accessible.
  • Check if image registry credentials are properly configured.

3. Node Issues and Failures

Symptoms:

• Nodes are NotReady.
• Pods are evicted or stuck.

Troubleshooting Steps:

• Check Node Status:
  • kubectl get nodes
  • Look for NotReady status.
• Describe Node:
  • kubectl describe node <node-name>
  • Review conditions and events.
• Azure Portal:
  • Use Azure Portal to check node health, logs, and metrics.
• Node Restart or Replacement:
  • Consider restarting the node: az vm restart --resource-group <rg> --name <vm-name>
  • For persistent issues, cordon and drain the node: kubectl cordon <node> and kubectl drain <node>
• Update Cluster:
  • Keep AKS and node pools updated to benefit from the latest fixes.

4. Persistent Storage Problems

Symptoms:

• Persistent volume claims (PVCs) stuck in Pending.
• Data loss or inaccessible storage.

Troubleshooting Steps:

• Check PVC Status:
  • kubectl get pvc --namespace <namespace>
  • Look for Pending status.
• Describe PVC:
  • kubectl describe pvc <pvc-name>
  • Check for errors related to storage class or provisioner.
• Storage Class Configuration:
  • Verify that the storage class is correctly configured.
  • Ensure the corresponding Azure disk or file share exists.
• Azure Storage Accounts:
  • Confirm sufficient quota and permissions.
• Provisioner Logs:
  • Check logs of the storage provisioner for errors.

5. Monitoring and Logs

Symptoms:

• Difficult to identify root cause due to lack of insights.

Troubleshooting Steps:

• Use Azure Monitor:
  • Enable and review AKS diagnostics.
  • Check metrics and alerts.
• Kubernetes Dashboard:
  • Use the dashboard for real-time visualization.
• kubectl top:
  • kubectl top nodes and kubectl top pods for resource usage.
• Event Logs:
  • kubectl get events --namespace <namespace>
  • Review recent cluster events for clues.

Conclusion

Troubleshooting AKS clusters involves a systematic approach—checking cluster health, examining nodes and pods, reviewing storage and network configurations, and utilizing monitoring tools. By familiarizing yourself with these common issues and their solutions, you can maintain a robust and resilient AKS environment.

Regular monitoring, timely updates, and proactive management are key to minimizing downtime and ensuring your containerized applications run smoothly on Azure Kubernetes Service.