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Containerization-Orchestration/Kubernetes/Storage/Pv.md
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Containerization-Orchestration/Kubernetes/Storage/Pv.md
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# 🌐 Kubernetes Persistent Volumes (PV) Cheat Sheet
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## 📦 What is a Persistent Volume (PV)?
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A **Persistent Volume (PV)** is a piece of storage in a Kubernetes cluster that can be:
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- **Pre-provisioned** by an administrator, or
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- **Dynamically provisioned** using a **StorageClass**.
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> PVs allow data to **persist beyond the lifecycle of individual Pods**.
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---
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## 📁 PV Storage Options
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### 1. **HostPath**
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- Mounts a file or directory from the host node’s filesystem into a Pod.
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- Only suitable for **single-node testing or development** environments.
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### 2. **Persistent Volume (PV) & Persistent Volume Claim (PVC)**
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- **PV**: Represents the actual physical or virtual storage resource.
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- **PVC**: A user's request for specific storage resources and access modes.
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---
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## 🧱 Kubernetes Storage Architecture
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1. **Persistent Volume (PV)** – The actual storage unit, managed by the admin or provisioned dynamically.
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2. **Persistent Volume Claim (PVC)** – A user’s request for a certain amount and type of storage.
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---
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## 🔄 PV Lifecycle Phases
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| **State** | **Description** |
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|---------------|---------------------------------------------|
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| Provisioning | PV is being created or initialized. |
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| Binding | PV is bound to a PVC. |
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| Using | PV is in use by a Pod. |
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| Releasing | PVC is deleted; PV becomes unbound. |
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| Reclaiming | Based on reclaim policy: |
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| | - `Delete`: Remove the storage. |
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| | - `Recycle`: Basic scrub (deprecated). |
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| | - `Retain`: Manual cleanup required. |
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---
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## 🔒 PV Access Modes
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| **Mode** | **Description** |
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|------------|-------------------------------------------------|
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| `RWO` | **ReadWriteOnce** – One node can read/write. |
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| `ROX` | **ReadOnlyMany** – Multiple nodes can read. |
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| `RWX` | **ReadWriteMany** – Multiple nodes can read/write. |
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| `RWOP` | **ReadWriteOncePod** – Only one Pod can mount it with read/write access. |
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---
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## 🛠️ CLI Commands to Manage PVs & PVCs
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```bash
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# List all Persistent Volumes
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kubectl get pv
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# List all Persistent Volume Claims
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kubectl get pvc
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# Edit a PVC
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kubectl edit pvc -n <namespace> <pvc-name>
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```
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---
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## 🚀 Example: Deployment with `hostPath` Volume
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```yaml
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: app-1
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namespace: dev
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spec:
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replicas: 3
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selector:
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matchLabels:
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name: nginx
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template:
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metadata:
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labels:
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name: nginx
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spec:
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containers:
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- name: nginx
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image: nginx
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ports:
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- containerPort: 80
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volumeMounts:
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- name: nginx-log
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mountPath: /var/log/nginx
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volumes:
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- name: nginx-log
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hostPath:
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path: /root/nginx/logs
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type: DirectoryOrCreate
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```
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### Valid `hostPath` Types:
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- `DirectoryOrCreate`
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- `Directory`
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- `FileOrCreate`
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- `File`
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- `Socket`
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- `CharDevice`
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- `BlockDevice`
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---
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## 📄 Example: Static Persistent Volume (PV)
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```yaml
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apiVersion: v1
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kind: PersistentVolume
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metadata:
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name: pv001
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spec:
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capacity:
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storage: 128Mi
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accessModes:
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- ReadWriteMany
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persistentVolumeReclaimPolicy: Retain
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```
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---
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## 📄 Example: Persistent Volume Claim (PVC)
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```yaml
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: pvc-2
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namespace: db
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spec:
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accessModes:
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- ReadWriteOnce
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resources:
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requests:
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storage: 64Mi
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```
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> ✅ To bind a PVC to a specific PV, add `volumeName: <pv-name>` in the PVC spec:
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```yaml
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volumeName: pv001
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```
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---
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## 🌐 NFS-Based Persistent Volume
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### Persistent Volume (PV)
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```yaml
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apiVersion: v1
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kind: PersistentVolume
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metadata:
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name: pv-nfs-2
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spec:
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capacity:
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storage: 128Mi
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accessModes:
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- ReadWriteMany
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persistentVolumeReclaimPolicy: Retain
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storageClassName: nginx-files
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mountOptions:
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- hard
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- nfsvers=4.2
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nfs:
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path: /root/Nginx_Files
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server: 192.168.6.160
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```
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### Persistent Volume Claim (PVC)
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```yaml
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apiVersion: v1
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kind: PersistentVolumeClaim
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metadata:
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name: pvc-1
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namespace: db
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spec:
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volumeName: pv-nfs-2
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accessModes:
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- ReadWriteMany
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resources:
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requests:
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storage: 64Mi
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storageClassName: nginx-files
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```
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---
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## 🏗️ Static StorageClass for Pre-Provisioned Volumes
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```yaml
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apiVersion: storage.k8s.io/v1
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kind: StorageClass
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metadata:
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name: nginx-files
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provisioner: kubernetes.io/no-provisioner
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```
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