my-docs/Containerization & Orchestration/Kubernetes/workloads/11-Pv.md

🌐 Kubernetes Persistent Volumes (PV) Cheat Sheet

📦 What is a Persistent Volume (PV)?

A Persistent Volume (PV) is a piece of storage in a Kubernetes cluster that is either:

• Pre-provisioned by an administrator, or
• Dynamically provisioned using StorageClasses.

It allows data to persist beyond the lifecycle of individual Pods.

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📁 PV Storage Options

1. HostPath

   • Mounts a file or directory from the host node’s filesystem into your Pod.
   • Useful only for single-node testing or development.

2. Using PV and PVC

   • PV (Persistent Volume): Represents the actual storage resource.
   • PVC (Persistent Volume Claim): A user's request for storage resources and access.

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🧱 Kubernetes Storage Layers

1. Persistent Volume (PV) – The actual storage unit.
2. Persistent Volume Claim (PVC) – A request for that storage.

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🔄 PV Lifecycle States

State	Description
Provisioning	PV is being prepared.
Binding	PV is bound to a PVC.
Using	PV is in use by a Pod.
Releasing	PVC is deleted; PV becomes unbound.
Reclaiming	Reclaim policy is applied:
	• Delete – Remove the storage.
	• Recycle – Basic scrub (deprecated).
	• Retain – Manual intervention required.

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🔒 PV Access Modes

Mode	Description
RWO	ReadWriteOnce – One node can read/write
ROX	ReadOnlyMany – Multiple nodes read-only
RWX	ReadWriteMany – Multiple nodes read/write
RWOP	ReadWriteOncePod – Only one Pod can use it

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🛠️ CLI Commands to Manage PVs

# List all Persistent Volumes
kubectl get pv

# List all Persistent Volume Claims
kubectl get pvc

# Edit a PVC
kubectl edit pvc -n <namespace> <pvc-name>

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🚀 Example 1: Deployment with hostPath Volume

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-1
  namespace: dev
  labels:
    app.kubernetes.io/name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: nginx
  template:
    metadata:
      labels:
        app.kubernetes.io/name: 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

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📂 Example 2: NFS-backed Persistent Volume

🧩 PersistentVolume Definition

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv1
spec:
  capacity:
    storage: 5Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: custom-name
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /nfs/data
    server: 192.168.1.10

📄 PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc1
  namespace: ns-test
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi
  storageClassName: custom-name

🚀 Deployment Using PVC

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-1
  namespace: dev
  labels:
    app.kubernetes.io/name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: nginx
  template:
    metadata:
      labels:
        app.kubernetes.io/name: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
          ports:
            - containerPort: 80
          volumeMounts:
            - name: nginx-log
              mountPath: /var/log/nginx
      volumes:
        - name: nginx-log
          persistentVolumeClaim:
            claimName: pvc1

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📝 Common Mistakes Fixed