Certified Kubernetes Application Developer (CKAD) Study Guide

Chapter 8. State Persistence

Each container running in a Pod provides a temporary filesystem. Applications running in the container can read from it and write to it. A container’s temporary filesystem is isolated from any other container or Pod and is not persisted beyond a Pod restart. The “State Persistence” section of the CKAD curriculum addresses the technical abstraction in Kubernetes responsible for persisting data beyond a container or Pod restart.

A Volume is a Kubernetes capability that persists data beyond a Pod restart. Essentially, a Volume is a directory that’s shareable between multiple containers of a Pod. You will learn about the different Volume types and the process for defining and mounting a Volume in a container.

Persistent Volumes are a specific category of the wider concept of Volumes. The mechanics for Persistent Volumes are slightly more complex. The Persistent Volume is the resource that actually persists the data to an underlying physical storage. The Persistent Volume Claim represents the connecting resource between a Pod and a Persistent Volume responsible for requesting the storage. Finally, the Pod needs to claim the Persistent Volume and mount it to a directory path available to the containers running inside of the Pod.

At a high level, this chapter covers the following concepts:

• Volume

• Persistent Volume

• Persistent Volume Claim

Understanding Volumes

Applications running in a container can use the temporary filesystem to read and write files. ...