Lesson 8: Persistent Storage in Kubernetes

In this lesson, we will explore how to manage persistent data in Kubernetes using Volumes and PersistentVolumeClaims (PVCs). Understanding these concepts is crucial for any application that requires data to persist beyond the lifecycle of individual pods.

What are Volumes?

In Kubernetes, a Volume is a directory that is accessible to the containers in a pod. It provides a way for containers to share data and ensures that the data persists even if the container is restarted. Kubernetes supports several types of volumes, including:

• emptyDir: A temporary volume that is created when a pod is assigned to a node and exists as long as that pod is running.
• hostPath: A volume that mounts a file or directory from the host node’s filesystem into your pod.
• PersistentVolume (PV): A piece of storage in the cluster that has been provisioned by an administrator.

What are PersistentVolumeClaims?

A PersistentVolumeClaim (PVC) is a request for storage by a user. It allows you to request a specific amount of storage without having to know the details of the underlying storage infrastructure. When a PVC is created, Kubernetes looks for a matching PV to bind to it.

How to Use Persistent Volumes and Claims

Step 1: Create a PersistentVolume

A PersistentVolume can be created using a YAML manifest. Here’s an example of a PV that uses NFS (Network File System):

apiVersion: v1
kind: PersistentVolume
metadata:
  name: my-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteMany
  nfs:
    path: /path/on/nfs
    server: nfs-server.example.com

Step 2: Create a PersistentVolumeClaim

Next, create a PVC that requests storage from the PV:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 5Gi

Step 3: Use PVC in a Pod

Now, you can use the PVC in a pod definition:

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
    - name: my-container
      image: nginx
      volumeMounts:
        - mountPath: /usr/share/nginx/html
          name: my-volume
  volumes:
    - name: my-volume
      persistentVolumeClaim:
        claimName: my-pvc

Best Practices

• Always use PVCs: Instead of directly using PVs, always create PVCs to abstract the underlying storage.
• Define access modes: Specify the access modes based on your application’s requirements (e.g., ReadWriteOnce, ReadWriteMany).
• Monitor storage usage: Keep track of your storage usage to avoid running out of space.

Common Mistakes

Avoid hardcoding storage details: Use PVCs to decouple your application from the underlying storage technology. Ignoring access modes: Ensure that the access modes specified in your PVC match those of the PV.

Summary of Concepts

Understanding these concepts will enable you to manage persistent storage effectively in your Kubernetes applications.

Exercise 1: Create a PersistentVolume

Create a PV using the provided YAML template. Make sure to adjust the path and server fields to your environment.

Exercise 2: Create a PersistentVolumeClaim

Create a PVC that requests 1Gi of storage. Use the YAML template provided in the lesson.

Exercise 3: Deploy a Pod with PVC

Modify the pod definition provided in the lesson to use your newly created PVC. Deploy the pod and verify that it can access the persistent storage.

• Volumes provide persistent data storage for containers in Kubernetes.
• PersistentVolumeClaims allow users to request storage without needing to know the details of the underlying infrastructure.
• Always use PVCs to abstract storage details and ensure proper access modes are set.
• Monitor your storage usage to prevent running out of space.