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update pv & pvc doc

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RadinPirouz
2025-10-08 20:15:41 +03:30
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Containerization-Orchestration/Kubernetes/Storage/Pv.md
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# 🌐 Kubernetes Persistent Volumes (PV) Cheat Sheet # Kubernetes Persistent Volumes (PV) Cheat Sheet
## 📦 What is a Persistent Volume (PV)? ## What is a Persistent Volume (PV)?
A **Persistent Volume (PV)** is a piece of storage in a Kubernetes cluster that can be: A **Persistent Volume (PV)** is a piece of storage in a Kubernetes cluster that can be:
- **Pre-provisioned** by an administrator, or * **Pre-provisioned** by an administrator, or
- **Dynamically provisioned** using a **StorageClass**. * **Dynamically provisioned** using a **StorageClass**.
> PVs allow data to **persist beyond the lifecycle of individual Pods**. PVs allow data to **persist beyond the lifecycle of individual Pods**.
--- ---
## 📁 PV Storage Options ## PV Storage Options
### 1. **HostPath** ### 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)** * Mounts a file or directory from the host node’s filesystem into a Pod.
- **PV**: Represents the actual physical or virtual storage resource. * Suitable **only for local development or single-node clusters** such as Minikube or Kind.
- **PVC**: A user's request for specific storage resources and access modes. * Not recommended for production workloads.
### 2. NFS
* Network File System; allows multiple Pods and nodes to share storage.
* Recommended for shared or distributed environments.
### 3. Cloud Volumes
* **AWS:** `awsElasticBlockStore`
* **GCP:** `gcePersistentDisk`
* **Azure:** `azureDisk` or `azureFile`
* **CSI Drivers:** Preferred modern approach for all major clouds and on-prem solutions.
--- ---
## 🧱 Kubernetes Storage Architecture ## Kubernetes Storage Architecture
1. **Persistent Volume (PV)** – The actual storage unit, managed by the admin or provisioned dynamically. 1. **Persistent Volume (PV)** – Represents the actual storage resource, managed by the cluster admin or a dynamic provisioner.
2. **Persistent Volume Claim (PVC)** – A user’s request for a certain amount and type of storage. 2. **Persistent Volume Claim (PVC)** – A user request for storage with specific size and access requirements.
3. **StorageClass** – Defines how dynamic provisioning should occur (provisioner, reclaim policy, parameters).
--- ---
## 🔄 PV Lifecycle Phases ## PV Lifecycle Phases
| **State** | **Description** | | State | Description |
|---------------|---------------------------------------------| | ------------- | -------------------------------------------------------- |
| Provisioning | PV is being created or initialized. | | **Available** | PV is ready to be bound. |
| Binding | PV is bound to a PVC. | | **Bound** | PV is bound to a PVC. |
| Using | PV is in use by a Pod. | | **Released** | PVC was deleted; PV is unbound but data may still exist. |
| Releasing | PVC is deleted; PV becomes unbound. | | **Failed** | Automatic cleanup failed. |
| Reclaiming | Based on reclaim policy: |
| | - `Delete`: Remove the storage. | ### Reclaim Policies:
| | - `Recycle`: Basic scrub (deprecated). |
| | - `Retain`: Manual cleanup required. | * **Delete:** Removes the underlying storage resource.
* **Retain:** Keeps data for manual recovery.
* **Recycle:** Deprecated (previously used to scrub the volume).
--- ---
## 🔒 PV Access Modes ## PV Access Modes
| **Mode** | **Description** | | Mode | Description |
|------------|-------------------------------------------------| | ------------------------- | -------------------------------------------------------------------- |
| `RWO` | **ReadWriteOnce** – One node can read/write. | | `ReadWriteOnce` (RWO) | One node can read/write. |
| `ROX` | **ReadOnlyMany** – Multiple nodes can read. | | `ReadOnlyMany` (ROX) | Many nodes can read. |
| `RWX` | **ReadWriteMany** – Multiple nodes can read/write. | | `ReadWriteMany` (RWX) | Many nodes can read/write. |
| `RWOP` | **ReadWriteOncePod** – Only one Pod can mount it with read/write access. | | `ReadWriteOncePod` (RWOP) | Only one Pod can mount it with read/write access (Kubernetes ≥1.22). |
--- ---
## 🛠️ CLI Commands to Manage PVs & PVCs ## CLI Commands to Manage PVs & PVCs
```bash ```bash
# List all Persistent Volumes # List all Persistent Volumes
kubectl get pv kubectl get pv
# List all Persistent Volume Claims # List all Persistent Volume Claims
kubectl get pvc kubectl get pvc -A
# Edit a PVC # Describe a specific PV or PVC
kubectl edit pvc -n <namespace> <pvc-name> kubectl describe pv <pv-name>
kubectl describe pvc <pvc-name> -n <namespace>
# Delete a PV or PVC
kubectl delete pv <pv-name>
kubectl delete pvc <pvc-name> -n <namespace>
``` ```
--- ---
## 🚀 Example: Deployment with `hostPath` Volume ## Example: Deployment with `hostPath` Volume
```yaml ```yaml
apiVersion: apps/v1 apiVersion: apps/v1
@@ -83,11 +101,11 @@ spec:
replicas: 3 replicas: 3
selector: selector:
matchLabels: matchLabels:
name: nginx app: nginx
template: template:
metadata: metadata:
labels: labels:
name: nginx app: nginx
spec: spec:
containers: containers:
- name: nginx - name: nginx
@@ -104,18 +122,15 @@ spec:
type: DirectoryOrCreate type: DirectoryOrCreate
``` ```
### Valid `hostPath` Types: **Valid `hostPath` Types:**
- `DirectoryOrCreate` `DirectoryOrCreate`, `Directory`, `FileOrCreate`, `File`, `Socket`, `CharDevice`, `BlockDevice`
- `Directory`
- `FileOrCreate`
- `File`
- `Socket`
- `CharDevice`
- `BlockDevice`
--- ---
## 📄 Example: Static Persistent Volume (PV) ## Example: Static Persistent Volume (PV)
**Important:** A PV **must specify a volume source type** (this was the cause of your validation error).
For example, this corrected PV uses `hostPath`:
```yaml ```yaml
apiVersion: v1 apiVersion: v1
@@ -128,11 +143,14 @@ spec:
accessModes: accessModes:
- ReadWriteMany - ReadWriteMany
persistentVolumeReclaimPolicy: Retain persistentVolumeReclaimPolicy: Retain
storageClassName: manual
hostPath:
path: /mnt/data/pv001
``` ```
--- ---
## 📄 Example: Persistent Volume Claim (PVC) ## Example: Persistent Volume Claim (PVC)
```yaml ```yaml
apiVersion: v1 apiVersion: v1
@@ -146,16 +164,18 @@ spec:
resources: resources:
requests: requests:
storage: 64Mi storage: 64Mi
storageClassName: manual
``` ```
> ✅ To bind a PVC to a specific PV, add `volumeName: <pv-name>` in the PVC spec: To bind this PVC to a specific PV manually:
```yaml ```yaml
volumeName: pv001 volumeName: pv001
``` ```
--- ---
## 🌐 NFS-Based Persistent Volume ## NFS-Based Persistent Volume
### Persistent Volume (PV) ### Persistent Volume (PV)
@@ -199,7 +219,7 @@ spec:
--- ---
## 🏗️ Static StorageClass for Pre-Provisioned Volumes ## Static StorageClass for Pre-Provisioned Volumes
```yaml ```yaml
apiVersion: storage.k8s.io/v1 apiVersion: storage.k8s.io/v1
@@ -207,4 +227,21 @@ kind: StorageClass
metadata: metadata:
name: nginx-files name: nginx-files
provisioner: kubernetes.io/no-provisioner provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
reclaimPolicy: Retain
``` ```
---
## Recommended Additions
1. **Always include `storageClassName`** to ensure predictable binding.
2. **Set `volumeBindingMode: WaitForFirstConsumer`** in StorageClasses for node-aware provisioning.
3. **Avoid using `hostPath` in multi-node clusters**; use NFS or CSI drivers.
4. **Check events** for troubleshooting PV/PVC binding:
```bash
kubectl describe pvc <pvc-name> -n <namespace>
```
5. **Automate cleanup** with proper reclaim policies or storage lifecycle controllers.