Kubernetes PVC Unbound: Troubleshooting Guide

• Introduction
• Step-by-Step Guide
• Code Example
• Additional Notes
• Summary
• Conclusion
• References

Troubleshooting MongoDB deployments on Kubernetes can be tricky. This guide outlines common issues and solutions to help you get your MongoDB instance up and running smoothly. We'll cover checks for PersistentVolumeClaims, StorageClasses, pod events, resource constraints, and more.

1. Check PersistentVolumeClaims (PVCs):

   kubectl get pvc

   Ensure your PVCs are in Bound state. If not, check your PersistentVolumes (PVs) and StorageClasses.

2. Verify StorageClass:

   kubectl describe pvc <pvc-name>

   Confirm the StorageClass used by your PVC exists and is correctly configured for your environment (e.g., local storage, cloud provider).

3. Inspect Pod Events:

   kubectl describe pod <pod-name>

   Look for events related to scheduling or volume mounting issues. Common messages include "Unschedulable" or "Failed to mount volumes".

4. Resource Constraints: Ensure your nodes have sufficient resources (CPU, memory, disk space) to run the MongoDB pod. Adjust resource requests and limits in your deployment YAML if needed.

5. Node Affinity/Taints and Tolerations: If using node selectors, affinity rules, taints, or tolerations, verify they are correctly configured and allow the MongoDB pod to be scheduled on suitable nodes.

6. Kompose for Migration (if applicable): If migrating from Docker Compose, Kompose can help generate Kubernetes YAML files. However, manually review and adjust the generated configurations for production use.

7. MongoDB Configuration:

   • Check MongoDB logs for errors related to data directory access or initialization.
   • Ensure the dbPath in your MongoDB configuration points to a persistent volume mount.

8. Clean Shutdown: If restarting a previously running pod, ensure a clean shutdown of MongoDB to prevent "dbPathInUse" errors.

9. Kubernetes Version Compatibility: Verify compatibility between your Kubernetes version and the MongoDB Docker image you are using.

10. Network Connectivity: Ensure the MongoDB pod can reach other necessary services, such as other replica set members, within the cluster network.

This document provides code examples for troubleshooting MongoDB on Kubernetes. It includes commands for checking PersistentVolumeClaims status, verifying StorageClass configuration, inspecting pod events for issues, and adjusting resource constraints in deployment YAML. It also covers node affinity configuration, Kompose usage for migration from Docker Compose, MongoDB configuration file settings, clean pod shutdown, Kubernetes version compatibility, and network connectivity troubleshooting within a MongoDB pod. Remember to replace placeholders with actual values and refer to official documentation for specific setups.

This document provides code examples and explanations for the troubleshooting steps outlined in the article.

1. Check PersistentVolumeClaims (PVCs):

kubectl get pvc

Example Output:

NAME        STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
mongo-pvc   Bound    pvc-f574989c-8b8c-4a4f-b15c-a8245c34645f   1Gi        RWX            local-storage   20h

Explanation: This command lists all PVCs in your namespace. Ensure the STATUS is Bound. If not, investigate your PVs and StorageClasses.

2. Verify StorageClass:

kubectl describe pvc mongo-pvc

Example Output (truncated):

Name:          mongo-pvc
Namespace:     default
StorageClass:  local-storage
Status:        Bound
...

Explanation: This command shows details about a specific PVC. Check the StorageClass field and ensure it matches your environment's configuration.

3. Inspect Pod Events:

kubectl describe pod mongo-pod

Example Output (truncated):

Events:
  Type     Reason                  Age                From               Message
  ----     ------                  ----               ----               -------
  Warning  FailedScheduling        3m                default-scheduler  0/3 nodes are available: 1 node(s) had taint {key=node-role.kubernetes.io/master:NoSchedule}, that the pod didn't tolerate, 2 Insufficient memory.

Explanation: This command displays pod events, including scheduling and volume mounting issues. Look for error messages like "Unschedulable" or "Failed to mount volumes".

4. Resource Constraints:

Example Deployment YAML (excerpt):

apiVersion: apps/v1
kind: Deployment
...
spec:
  ...
  resources:
    limits:
      cpu: "1000m"
      memory: "2Gi"
    requests:
      cpu: "500m"
      memory: "1Gi"

Explanation: Adjust the limits and requests for CPU and memory based on your MongoDB workload and node capacity.

5. Node Affinity/Taints and Tolerations:

Example Deployment YAML (excerpt):

apiVersion: apps/v1
kind: Deployment
...
spec:
  ...
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: kubernetes.io/hostname
            operator: In
            values:
            - mongo-node

Explanation: This example demonstrates node affinity, ensuring the pod is scheduled on a node with the hostname "mongo-node". Adjust selectors, taints, and tolerations based on your requirements.

6. Kompose for Migration (if applicable):

kompose convert -f docker-compose.yml

Explanation: This command converts a Docker Compose file (docker-compose.yml) into Kubernetes YAML files. Review and modify the generated files for production readiness.

7. MongoDB Configuration:

Example MongoDB Configuration File (excerpt):

storage:
  dbPath: /data/db

Explanation: Ensure the dbPath points to the directory where your persistent volume is mounted within the container.

8. Clean Shutdown:

kubectl delete pod mongo-pod --grace-period=30 --force

Explanation: This command gracefully terminates the pod with a 30-second grace period, allowing MongoDB to shut down cleanly.

9. Kubernetes Version Compatibility:

Refer to the MongoDB documentation and Docker Hub for compatibility information between your Kubernetes version and the MongoDB Docker image.

10. Network Connectivity:

Use kubectl exec to run network troubleshooting commands within the MongoDB pod:

kubectl exec -it mongo-pod -- nslookup <service-name>
kubectl exec -it mongo-pod -- ping <ip-address>

Explanation: These commands test DNS resolution and network connectivity from within the pod to other services or IP addresses.

Remember to replace placeholders like <pvc-name>, <pod-name>, <service-name>, and <ip-address> with your actual values. This guide provides a starting point for troubleshooting MongoDB on Kubernetes. Always consult the official documentation for your specific setup and tools.

• Liveness and Readiness Probes: Implement liveness and readiness probes in your MongoDB deployment to ensure the container is healthy and ready to accept traffic. This helps Kubernetes automatically restart unhealthy pods or remove them from service endpoints.
• Security:
  • Authentication and Authorization: Enable access control and configure authentication mechanisms in your MongoDB deployment to secure your data.
  • Network Policies: Use network policies to restrict traffic to your MongoDB pods, limiting access to authorized clients and services only.
• Monitoring and Logging:
  • Metrics: Collect and monitor essential metrics like memory usage, connections, operations, and replication lag to ensure optimal performance and identify potential issues.
  • Logging: Configure centralized logging to aggregate and analyze MongoDB logs for troubleshooting and performance tuning.
• Backups and Disaster Recovery:
  • Regular Backups: Implement a robust backup strategy to protect your data against accidental loss or corruption.
  • Disaster Recovery Plan: Have a disaster recovery plan in place to restore your MongoDB deployment in case of a major outage.
• Scaling:
  • Horizontal Pod Scaling: Use Horizontal Pod Autoscaler (HPA) to automatically adjust the number of MongoDB pods based on CPU utilization or other metrics.
  • MongoDB Replica Sets: For high availability and fault tolerance, deploy MongoDB as a replica set with multiple instances across different nodes.
• StatefulSet: Use StatefulSet instead of Deployment for managing MongoDB deployments, as it provides guarantees about the ordering and uniqueness of pods, which is crucial for stateful applications like databases.
• Resource Limits: Set resource limits (CPU, memory) for your MongoDB containers to prevent resource starvation and ensure predictable performance.
• Image Optimization: Use optimized Docker images for MongoDB to reduce image size and improve startup time.
• Keep Updated: Regularly update your Kubernetes cluster, MongoDB Docker images, and other related components to benefit from the latest security patches and performance improvements.

Remember that these notes provide general guidance. Always refer to the official MongoDB and Kubernetes documentation for specific instructions and best practices tailored to your environment and deployment needs.

This guide provides a concise checklist for troubleshooting MongoDB deployments on Kubernetes:

Storage & Scheduling:

• PVC Status: Ensure all PersistentVolumeClaims (PVCs) are in a Bound state using kubectl get pvc. Investigate PersistentVolumes (PVs) and StorageClasses if not.
• StorageClass Configuration: Verify the StorageClass used by your PVC is correctly configured for your environment (e.g., local storage, cloud provider) using kubectl describe pvc <pvc-name>.
• Pod Scheduling: Inspect pod events for scheduling or volume mounting issues using kubectl describe pod <pod-name>. Look for messages like "Unschedulable" or "Failed to mount volumes".
• Resource Availability: Ensure nodes have sufficient resources (CPU, memory, disk space) for the MongoDB pod. Adjust resource requests and limits in your deployment YAML if needed.
• Node Selection: If using node selectors, affinity rules, taints, or tolerations, verify they are correctly configured to allow scheduling on suitable nodes.

MongoDB Specific:

• Configuration: Check MongoDB logs for errors related to data directory access or initialization. Ensure the dbPath points to a persistent volume mount.
• Clean Shutdown: Ensure a clean shutdown of MongoDB before restarting a pod to prevent "dbPathInUse" errors.

Other Considerations:

• Kompose Migration: If migrating from Docker Compose, review and adjust Kompose-generated Kubernetes YAML files for production use.
• Version Compatibility: Verify compatibility between your Kubernetes version and the MongoDB Docker image.
• Network Connectivity: Ensure the MongoDB pod can reach other necessary services within the cluster network.

This guide provides a starting point for troubleshooting MongoDB deployments on Kubernetes, covering storage and scheduling, MongoDB-specific configurations, and other crucial considerations. Remember to consult official documentation for specific setups and always prioritize security, monitoring, backups, and disaster recovery in your deployment strategy. By systematically addressing potential issues and following best practices, you can ensure a robust and reliable MongoDB deployment on your Kubernetes cluster.

• Kompose : migration facile de Docker Compose à Kubernetes | Vous souhaitez migrer vos applications Docker sur Kubernetes ? Kompose peut vous aider à gagner du temps dans la migration !
• kubernetes - failing k8s mongodb pod after some time ... | Nov 6, 2022 ... K8s pod has unbound immediate PersistentVolumeClaims - mongoDB · 1 · K8s ... mongo db pod on bare metal kubernetese cluster is always pending.