my-docs/Containerization-Orchestration/Kubernetes/Storage/pv-pvc.md

Kubernetes Persistent Volumes (PV) – Technical Reference Guide

1. Overview

A Persistent Volume (PV) is a storage resource in Kubernetes that allows data to persist beyond the lifecycle of Pods. Persistent Volumes can be:

• Pre-provisioned by a cluster administrator, or
• Dynamically provisioned using a StorageClass.

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2. PV Storage Options

2.1 HostPath

• Mounts a directory or file from the host node’s filesystem into a Pod.
• Suitable only for local development or single-node clusters (e.g., Minikube, Kind).
• Not recommended for production environments.

2.2 NFS

• Uses Network File System (NFS) to allow multiple Pods and nodes to share storage.
• Recommended for shared or distributed setups.

2.3 Cloud Volumes

• AWS: awsElasticBlockStore
• GCP: gcePersistentDisk
• Azure: azureDisk or azureFile
• CSI Drivers: Preferred for all modern cloud and on-prem environments.

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3. Kubernetes Storage Architecture

1. Persistent Volume (PV): Represents the actual storage resource, either statically created or dynamically provisioned.
2. Persistent Volume Claim (PVC): A user request for storage of specific size and access modes.
3. StorageClass: Defines dynamic provisioning behavior (provisioner, reclaim policy, parameters).

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4. PV Lifecycle Phases

State	Description
Available	PV is ready to be bound to a claim.
Bound	PV is bound to a PVC.
Released	PVC was deleted; PV is unbound but retains data.
Failed	Automatic cleanup failed.

Reclaim Policies

• Delete: Deletes the underlying storage resource.
• Retain: Keeps the data for manual recovery.
• Recycle: Deprecated (was used to scrub the volume).

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5. PV Access Modes

Access Mode	Description
ReadWriteOnce (RWO)	Volume can be mounted as read-write by a single node.
ReadOnlyMany (ROX)	Volume can be mounted read-only by multiple nodes.
ReadWriteMany (RWX)	Volume can be mounted as read-write by multiple nodes.
ReadWriteOncePod (RWOP)	Volume can be mounted read-write by a single Pod. (≥ v1.22)

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6. CLI Commands

# List all Persistent Volumes
kubectl get pv

# List all Persistent Volume Claims (across all namespaces)
kubectl get pvc -A

# Describe a specific PV or PVC
kubectl describe pv <pv-name>
kubectl describe pvc <pvc-name> -n <namespace>

# Delete a PV or PVC
kubectl delete pv <pv-name>
kubectl delete pvc <pvc-name> -n <namespace>

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7. Example: Deployment with HostPath Volume

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-1
  namespace: dev
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
          ports:
            - containerPort: 80
          volumeMounts:
            - name: nginx-log
              mountPath: /var/log/nginx
      volumes:
        - name: nginx-log
          hostPath:
            path: /root/nginx/logs
            type: DirectoryOrCreate

Valid hostPath types: DirectoryOrCreate, Directory, FileOrCreate, File, Socket, CharDevice, BlockDevice

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8. Example: Static Persistent Volume (PV)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv001
spec:
  capacity:
    storage: 128Mi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: /mnt/data/pv001

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9. Example: Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-2
  namespace: db
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 64Mi
  storageClassName: manual
  volumeName: pv001

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10. Example: NFS-Based PV and PVC

Persistent Volume (PV)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-nfs-2
spec:
  capacity:
    storage: 128Mi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: nginx-files
  mountOptions:
    - hard
    - nfsvers=4.2
  nfs:
    path: /root/Nginx_Files
    server: 192.168.6.160

Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-1
  namespace: db
spec:
  volumeName: pv-nfs-2
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 64Mi
  storageClassName: nginx-files

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11. Example: Static StorageClass

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nginx-files
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
reclaimPolicy: Retain

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12. Example: Nginx Deployment Using PVC

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  namespace: web-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app_type: nginx-web
  template:
    metadata:
      labels:
        app_type: nginx-web
    spec:
      containers:
        - name: nginx
          image: nginx:latest
          ports:
            - containerPort: 80
          volumeMounts:
            - name: nginx-configs-volume
              mountPath: /etc/nginx/conf.d/default.conf
              subPath: reverse_proxy.conf
            - name: nginx-logs-volume
              mountPath: /var/log/nginx
      volumes:
        - name: nginx-configs-volume
          configMap:
            name: nginx-configs
        - name: nginx-logs-volume
          persistentVolumeClaim:
            claimName: nginx-pvc

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13. Best Practices and Recommendations

1. Always specify storageClassName for predictable PV/PVC binding.

2. Use volumeBindingMode: WaitForFirstConsumer to ensure node-aware provisioning.

3. Avoid hostPath in multi-node or production clusters; use NFS or CSI drivers instead.

4. Monitor events for troubleshooting binding issues:

   kubectl describe pvc <pvc-name> -n <namespace>
   

5. Implement proper reclaim policies or automated cleanup mechanisms for storage lifecycle management.