Kubernetes Cookbook, 2nd Edition

Chapter 8. Volumes and Configuration Data

A volume in Kubernetes is a directory accessible to all containers running in a pod, with the additional guarantee that the data is preserved across restarts of individual containers.

We can distinguish between a few types of volumes:

• Node-local ephemeral volumes, such as emptyDir

• Generic networked volumes, such as nfs or cephfs

• Cloud provider–specific volumes, such as AWS EBS or AWS EFS

• Special-purpose volumes, such as secret or configMap

Which volume type you choose depends entirely on your use case. For example, for a temporary scratch space, an emptyDir would be fine, but when you need to make sure your data survives node failures, you’ll want to look into more resilient alternatives or cloud provider–specific solutions.

8.1 Exchanging Data Between Containers via a Local Volume

Problem

You have two or more containers running in a pod and want to be able to exchange data via filesystem operations.

Solution

Use a local volume of type emptyDir.

The starting point is the following pod manifest, exchangedata.yaml, which has two containers (c1 and c2) that each mount the local volume xchange into their filesystem, using different mount points:

apiVersion: v1
kind: Pod
metadata:
  name: sharevol
spec:
  containers:
  - name: c1
    image: ubuntu:20.04
    command:
      - "bin/bash"
      - "-c"
      - "sleep 10000"
    volumeMounts:
      - name: xchange
        mountPath: "/tmp/xchange"
  - name: c2
    image: ubuntu:20.04
    command:
      - "bin/bash"
      - "-c"
      - "sleep ...