nginx use volume , PVC and PV in Open shift - unix1998/technical_notes GitHub Wiki

When deploying an Nginx application with multiple replicas (or pods) in OpenShift (or Kubernetes), there are some best practices and considerations to keep in mind for handling persistent storage, especially when using Persistent Volume Claims (PVCs). Let's break down the scenario and the common settings for such an application.

Scenario: Nginx with 3 Replicas

1. Nginx Configuration Folder:

   • Contains configuration files like nginx.conf, site-specific configurations, etc.
   • Typically, this data is shared across all replicas to ensure consistent configuration.

2. Document Root:

   • Contains the web content (HTML, CSS, JS files, etc.) served by Nginx.
   • This data can also be shared across replicas or managed individually, depending on the use case.

Using PVCs with Nginx

1. Config Folder and Document Root as PVCs:

   • You can indeed have two separate PVCs: one for the Nginx configuration and one for the document root.

2. Access Modes:

   • ReadWriteMany (RWX): This mode allows the volume to be mounted as read-write by many nodes. This is suitable if you need multiple replicas (pods) to write to the same volume.
   • ReadOnlyMany (ROX): This mode allows the volume to be mounted as read-only by many nodes. This is useful if the content doesn't change frequently and you want to share it across multiple replicas without risking concurrent writes.
   • ReadWriteOnce (RWO): This mode allows the volume to be mounted as read-write by a single node. This is not suitable for scenarios where multiple replicas need access to the same volume.

Best Practices and Common Settings

1. Using ReadWriteMany (RWX):

   • Shared Configuration and Content: If your Nginx configuration and document root need to be the same across all replicas, using PVCs with RWX access mode makes sense. This ensures consistency and simplifies management.
   • Cluster File System: Ensure your underlying storage supports RWX. Not all storage backends in Kubernetes support RWX. Options like NFS, GlusterFS, or other distributed file systems are typically used.

2. Alternative Approaches:

   • ConfigMap for Configuration: For the Nginx configuration, consider using a ConfigMap. ConfigMaps can be mounted as files inside your pods and are suitable for configuration data. This way, you don't need a PVC for the config folder.
   • Separate Document Roots: Depending on the application, you might want to keep the document root separate for each replica (using RWO PVCs) if the content changes frequently and independently for each pod.
   • Immutable Content: If the document root content is immutable (doesn't change after deployment), you can use a ConfigMap for small amounts of data or a read-only PV.

Example Deployment Configuration

Here's an example of how you might configure your deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        volumeMounts:
        - name: nginx-config
          mountPath: /etc/nginx
        - name: document-root
          mountPath: /usr/share/nginx/html
      volumes:
      - name: nginx-config
        persistentVolumeClaim:
          claimName: nginx-config-pvc
      - name: document-root
        persistentVolumeClaim:
          claimName: document-root-pvc
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nginx-config-pvc
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: document-root-pvc
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 10Gi

Summary

• Use RWX PVCs: If you need shared configuration and document root across multiple replicas, use PVCs with RWX access mode.
• Consider ConfigMap: For static and small configuration files, ConfigMaps are an excellent alternative to PVCs.
• Storage Backend: Ensure your storage backend supports the RWX access mode.

This approach ensures consistency and manageability for your Nginx deployment in OpenShift.