279 lines
6.5 KiB
Markdown
279 lines
6.5 KiB
Markdown
# **Kubernetes Persistent Volumes (PV) – Technical Reference Guide**
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## **1. Overview**
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A **Persistent Volume (PV)** is a storage resource in Kubernetes that allows data to persist beyond the lifecycle of Pods.
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Persistent Volumes can be:
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* **Pre-provisioned** by a cluster administrator, or
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* **Dynamically provisioned** using a **StorageClass**.
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---
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## **2. PV Storage Options**
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### **2.1 HostPath**
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* Mounts a directory or file from the host node’s filesystem into a Pod.
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* Suitable only for **local development** or **single-node clusters** (e.g., Minikube, Kind).
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* **Not recommended** for production environments.
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### **2.2 NFS**
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* Uses Network File System (NFS) to allow multiple Pods and nodes to share storage.
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* Recommended for **shared or distributed** setups.
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### **2.3 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 for all modern cloud and on-prem environments.
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---
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## **3. Kubernetes Storage Architecture**
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1. **Persistent Volume (PV):** Represents the actual storage resource, either statically created or dynamically provisioned.
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2. **Persistent Volume Claim (PVC):** A user request for storage of specific size and access modes.
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3. **StorageClass:** Defines dynamic provisioning behavior (provisioner, reclaim policy, parameters).
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---
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## **4. PV Lifecycle Phases**
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| **State** | **Description** |
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| ------------- | ------------------------------------------------ |
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| **Available** | PV is ready to be bound to a claim. |
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| **Bound** | PV is bound to a PVC. |
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| **Released** | PVC was deleted; PV is unbound but retains data. |
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| **Failed** | Automatic cleanup failed. |
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### **Reclaim Policies**
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* **Delete:** Deletes the underlying storage resource.
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* **Retain:** Keeps the data for manual recovery.
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* **Recycle:** Deprecated (was used to scrub the volume).
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---
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## **5. PV Access Modes**
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| **Access Mode** | **Description** |
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| ------------------------- | ----------------------------------------------------------- |
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| `ReadWriteOnce` (RWO) | Volume can be mounted as read-write by a single node. |
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| `ReadOnlyMany` (ROX) | Volume can be mounted read-only by multiple nodes. |
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| `ReadWriteMany` (RWX) | Volume can be mounted as read-write by multiple nodes. |
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| `ReadWriteOncePod` (RWOP) | Volume can be mounted read-write by a single Pod. (≥ v1.22) |
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---
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## **6. CLI Commands**
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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 (across all namespaces)
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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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## **7. 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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## **8. 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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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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## **9. 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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volumeName: pv001
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```
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---
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## **10. Example: NFS-Based PV and PVC**
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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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## **11. Example: Static StorageClass**
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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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## **12. Example: Nginx Deployment Using PVC**
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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: nginx
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namespace: web-app
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spec:
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replicas: 1
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selector:
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matchLabels:
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app_type: nginx-web
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template:
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metadata:
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labels:
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app_type: nginx-web
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spec:
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containers:
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- name: nginx
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image: nginx:latest
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ports:
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- containerPort: 80
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volumeMounts:
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- name: nginx-configs-volume
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mountPath: /etc/nginx/conf.d/default.conf
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subPath: reverse_proxy.conf
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- name: nginx-logs-volume
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mountPath: /var/log/nginx
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volumes:
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- name: nginx-configs-volume
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configMap:
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name: nginx-configs
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- name: nginx-logs-volume
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persistentVolumeClaim:
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claimName: nginx-pvc
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```
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---
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## **13. Best Practices and Recommendations**
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1. **Always specify `storageClassName`** for predictable PV/PVC binding.
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2. **Use `volumeBindingMode: WaitForFirstConsumer`** to ensure node-aware provisioning.
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3. **Avoid `hostPath`** in multi-node or production clusters; use NFS or CSI drivers instead.
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4. **Monitor events** for troubleshooting binding issues:
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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. **Implement proper reclaim policies** or automated cleanup mechanisms for storage lifecycle management.
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