Common Issues and Solutions
This section covers frequent problems encountered when working with Azure Kubernetes Service (AKS). We'll provide actionable steps to diagnose and resolve these issues.
Pod & Container Issues
Problems within pods are the most common. Here's how to approach them:
Pod Stuck in Pending State
A pod might remain in the Pending state if the scheduler cannot find a suitable node to run it. Common causes include:
- Insufficient Resources: The cluster lacks nodes with enough CPU or memory. Check resource requests and limits defined in your pod specifications.
- Taints and Tolerations: Nodes might have taints that prevent the pod from being scheduled. Verify taints on nodes and ensure your pods have corresponding tolerations.
- PersistentVolumeClaim (PVC) Issues: If the pod requires persistent storage, a pending PVC can block its startup. Check the status of your PVCs and the underlying storage provisioner.
Tip
Use kubectl describe pod to view events that might explain why a pod is pending.
Container CrashLoopBackOff
This error indicates that a container in a pod is repeatedly starting, crashing, and restarting. Debugging steps:
- Check Container Logs: The most crucial step is to examine the application logs. Use
kubectl logs.-c -n - Resource Limits: If memory limits are too low, the application might be OOMKilled (Out Of Memory killed).
- Application Errors: The application itself might have bugs or configuration issues causing it to crash.
- Readiness/Liveness Probes: Misconfigured probes can cause Kubernetes to restart healthy containers.
kubectl logs my-app-pod-xyz -c my-app-container -n default
Image Pull Errors (ErrImagePull, ImagePullBackOff)
These errors occur when Kubernetes cannot pull the container image. Solutions:
- Image Name & Tag: Double-check that the image name and tag are spelled correctly and exist in the registry.
- Registry Authentication: For private registries, ensure your
imagePullSecretsare correctly configured and contain valid credentials. - Network Connectivity: Verify that your AKS nodes can reach the container registry.
Networking Issues
Network problems can manifest as connectivity issues between pods, services, or to external resources.
Service Not Reachable
If your service endpoint is inaccessible:
- Service Definition: Verify the
selectorin your Service definition correctly matches the labels on your pods. - EndpointSlice: Check if the Service has healthy endpoints. Use
kubectl get endpointslices -l kubernetes.io/service-name=.-n - Network Policies: Ensure no Network Policies are blocking traffic to or from the pods backing the service.
- Ingress/Load Balancer: If accessing via an Ingress or Load Balancer, check their configurations and logs.
DNS Resolution Problems
Pods may fail to resolve hostnames:
- CoreDNS/Kube-DNS: Check the health of your cluster's DNS service (usually CoreDNS). Use
kubectl get pods -n kube-system -l k8s-app=kube-dns. - Node Network: Ensure nodes can reach external DNS servers.
- Service Discovery: Verify your Service names are correctly formatted (e.g.,
service-name.namespace.svc.cluster.local).
Storage Issues
Problems related to persistent storage.
PersistentVolumeClaim (PVC) Not Bound
A PVC might fail to bind to a PersistentVolume (PV):
- Storage Class: Ensure a Storage Class is specified in the PVC and that it exists and is correctly configured. For Azure, this might be
managed-csior similar. - Dynamic Provisioning: If dynamic provisioning is used, check the logs of the storage provisioner pod.
- Access Modes: Verify that the access modes (e.g.,
ReadWriteOnce,ReadOnlyMany) requested by the PVC are compatible with the underlying storage and the PV.
Node & Cluster Issues
Problems affecting the nodes or the overall cluster health.
Nodes Not Ready
If nodes show as NotReady:
- Kubelet Health: Check the status of the Kubelet service on the affected node.
- Resource Saturation: The node might be out of disk space, memory, or CPU.
- Network Connectivity: The node might have lost network connectivity to the control plane.
- AKS Service Health: Check the Azure Service Health dashboard for any ongoing issues with AKS in your region.
kubectl get nodes
Performance Tuning
Optimizing AKS performance.
- Resource Requests/Limits: Properly set CPU and memory requests and limits for your containers to ensure predictable performance and efficient scheduling.
- Horizontal Pod Autoscaler (HPA): Automate scaling of your deployments based on CPU or memory usage.
- Cluster Autoscaler: Automatically adjust the number of nodes in your node pools based on pending pods.
- Node Pool Sizing: Choose appropriate VM sizes for your node pools based on workload requirements.
Security Concerns
Addressing security vulnerabilities.
- RBAC: Implement Role-Based Access Control (RBAC) to manage permissions effectively.
- Secrets Management: Use Kubernetes Secrets or Azure Key Vault for sensitive information.
- Network Policies: Restrict network traffic between pods.
- Image Scanning: Regularly scan container images for vulnerabilities.
Advanced Diagnostics
For deeper troubleshooting, consider these tools and techniques:
- AKS Diagnostics: Utilize the built-in diagnostics tool in the Azure portal for AKS.
- Metrics Server: Install Metrics Server to gather resource utilization data for pods and nodes.
- Prometheus & Grafana: Deploy monitoring stacks for in-depth observability.
- AKS Troubleshoot Command: The
aks troubleshootercommand-line tool can help diagnose common cluster issues.
By systematically approaching these common areas, you can efficiently diagnose and resolve most issues within your Azure Kubernetes Service deployments.