my-docs/Containerization & Orchestration/Kubernetes/Storage/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 can be:

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

PVs allow 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 a Pod.
• Only suitable for single-node testing or development environments.

2. Persistent Volume (PV) & Persistent Volume Claim (PVC)

• PV: Represents the actual physical or virtual storage resource.
• PVC: A user's request for specific storage resources and access modes.

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🧱 Kubernetes Storage Architecture

1. Persistent Volume (PV) – The actual storage unit, managed by the admin or provisioned dynamically.
2. Persistent Volume Claim (PVC) – A user’s request for a certain amount and type of storage.

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🔄 PV Lifecycle Phases

State	Description
Provisioning	PV is being created or initialized.
Binding	PV is bound to a PVC.
Using	PV is in use by a Pod.
Releasing	PVC is deleted; PV becomes unbound.
Reclaiming	Based on reclaim policy:
	- Delete: Remove the storage.
	- Recycle: Basic scrub (deprecated).
	- Retain: Manual cleanup required.

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🔒 PV Access Modes

Mode	Description
RWO	ReadWriteOnce – One node can read/write.
ROX	ReadOnlyMany – Multiple nodes can read.
RWX	ReadWriteMany – Multiple nodes can read/write.
RWOP	ReadWriteOncePod – Only one Pod can mount it with read/write access.

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🛠️ CLI Commands to Manage PVs & PVCs

# 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: Deployment with hostPath Volume

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

Valid hostPath Types:

• DirectoryOrCreate
• Directory
• FileOrCreate
• File
• Socket
• CharDevice
• BlockDevice

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📄 Example: Static Persistent Volume (PV)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv001
spec:
  capacity:
    storage: 128Mi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain

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📄 Example: Persistent Volume Claim (PVC)

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

✅ To bind a PVC to a specific PV, add volumeName: <pv-name> in the PVC spec:

volumeName: pv001

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🌐 NFS-Based Persistent Volume

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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🏗️ Static StorageClass for Pre-Provisioned Volumes

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