# 🌐 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**.

---

## 📁 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.

---

## 🧱 Kubernetes Storage Layers

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

---

## 🔄 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. |

---

## 🔒 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 |

---

## 🛠️ CLI Commands to Manage PVs

```bash
# 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>
```

---

## 🚀 Example 1: Deployment with `hostPath` Volume

```yaml
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
```


---

## 📂 Example 2: NFS-backed Persistent Volume

### 🧩 PersistentVolume Definition

```yaml
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

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

### 🚀 Deployment Using PVC

```yaml
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
```

---

## 📝 Common Mistakes Fixed