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Persistent Volumes

Goals​

  1. Understand Kubernetes Persistent Volumes:
    • Learn what a Persistent Volume (PV) is and its role in Kubernetes storage architecture.
  2. Basic Example(s):
    • Provide (a) basic example(s) of Persistent Volume and Persistent Volume Claim (PVC) resources.
    • Show how to define a PV and PVC using YAML.
  3. Persistent Volume Spec Explanation:
    • Explain the components of the Persistent Volume specification using the example(s) above.
  4. Persistent Volume Claims:
    • Describe the relationship between Persistent Volumes and Persistent Volume Claims.
  5. Exercise:
    • Hands-on activity to create and use a Persistent Volume.

Understanding Kubernetes Persistent Volumes​

A Persistent Volume (PV) in Kubernetes is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes. PVs are independent of the lifecycle of a pod and provide a way to persist data beyond the lifespan of individual pods.

Basic Persistent Volume Example​

Simple Persistent Volume and Persistent Volume Claim​

Here is a basic example of a Kubernetes Persistent Volume and Persistent Volume Claim in YAML:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: example-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: /mnt/data
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: example-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: manual

This example defines a 1Gi PV using a hostPath and a PVC requesting 1Gi of storage.

Save this to a file pv-pvc.yaml and create the resources using:

> kubectl apply -f pv-pvc.yaml
persistentvolume/example-pv created
persistentvolumeclaim/example-pvc created

Persistent Volume Spec Explanation​

  1. apiVersion: v1 (API group and version)
  2. kind: PersistentVolume (type of the resource)
  3. metadata: ObjectMeta
  4. spec: PersistentVolumeSpec
  5. status: PersistentVolumeStatus

Persistent Volume Claims​

  • A Persistent Volume Claim (PVC) is a request for storage by a user. It is similar to a pod in that pods consume node resources, and PVCs consume PV resources.
  • PVCs can request specific size and access modes (e.g., ReadWriteOnce, ReadOnlyMany).

Exercises​

Exercise 1: Create a Simple Persistent Volume​

Objective: Deploy an application that uses a Persistent Volume for storage.

Task:

  • Define a Persistent Volume with a suitable storage capacity.
  • Create a Persistent Volume Claim to request storage.
  • Deploy a pod that uses the PVC for persistent storage.
  • Verify that the pod can write and read data from the Persistent Volume.
tip

Make sure your cluster has a storage provider configured. For local testing, using a hostPath as shown in the example above is a simple way to simulate PV functionality.