change pv doc name
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Containerization-Orchestration/Kubernetes/Storage/pv-pvc.md
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Containerization-Orchestration/Kubernetes/Storage/pv-pvc.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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* Suitable **only for local development or single-node clusters** such as Minikube or Kind.
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* Not recommended for production workloads.
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### 2. NFS
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* Network File System; allows multiple Pods and nodes to share storage.
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* Recommended for shared or distributed environments.
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### 3. Cloud Volumes
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* **AWS:** `awsElasticBlockStore`
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* **GCP:** `gcePersistentDisk`
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* **Azure:** `azureDisk` or `azureFile`
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* **CSI Drivers:** Preferred modern approach for all major clouds and on-prem solutions.
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---
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## Kubernetes Storage Architecture
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1. **Persistent Volume (PV)** – Represents the actual storage resource, managed by the cluster admin or a dynamic provisioner.
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2. **Persistent Volume Claim (PVC)** – A user request for storage with specific size and access requirements.
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3. **StorageClass** – Defines how dynamic provisioning should occur (provisioner, reclaim policy, parameters).
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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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| **Available** | PV is ready to be bound. |
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| **Bound** | PV is bound to a PVC. |
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| **Released** | PVC was deleted; PV is unbound but data may still exist. |
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| **Failed** | Automatic cleanup failed. |
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### Reclaim Policies:
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* **Delete:** Removes the underlying storage resource.
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* **Retain:** Keeps data for manual recovery.
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* **Recycle:** Deprecated (previously used to scrub the volume).
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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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| `ReadWriteOnce` (RWO) | One node can read/write. |
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| `ReadOnlyMany` (ROX) | Many nodes can read. |
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| `ReadWriteMany` (RWX) | Many nodes can read/write. |
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| `ReadWriteOncePod` (RWOP) | Only one Pod can mount it with read/write access (Kubernetes ≥1.22). |
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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 -A
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# Describe a specific PV or PVC
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kubectl describe pv <pv-name>
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kubectl describe pvc <pvc-name> -n <namespace>
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# Delete a PV or PVC
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kubectl delete pv <pv-name>
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kubectl delete pvc <pvc-name> -n <namespace>
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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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app: nginx
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template:
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metadata:
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labels:
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app: 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`, `Directory`, `FileOrCreate`, `File`, `Socket`, `CharDevice`, `BlockDevice`
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---
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## Example: Static Persistent Volume (PV)
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**Important:** A PV **must specify a volume source type** (this was the cause of your validation error).
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For example, this corrected PV uses `hostPath`:
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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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storageClassName: manual
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hostPath:
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path: /mnt/data/pv001
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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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storageClassName: manual
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```
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To bind this PVC to a specific PV manually:
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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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volumeBindingMode: WaitForFirstConsumer
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reclaimPolicy: Retain
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```
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---
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## Recommended Additions
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1. **Always include `storageClassName`** to ensure predictable binding.
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2. **Set `volumeBindingMode: WaitForFirstConsumer`** in StorageClasses for node-aware provisioning.
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3. **Avoid using `hostPath` in multi-node clusters**; use NFS or CSI drivers.
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4. **Check events** for troubleshooting PV/PVC binding:
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```bash
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kubectl describe pvc <pvc-name> -n <namespace>
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```
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5. **Automate cleanup** with proper reclaim policies or storage lifecycle controllers.
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