Environment Variables

Part of the Introduction to Kubernetes section of Coddy's Terminal journey. Lesson 28 of 45.

A container reads its configuration from environment variables. In a manifest they are listed under the container's env, each with a name and a value:

containers:
  - name: app
    image: busybox
    env:
      - name: GREETING
        value: hello

Instead of a fixed value, a variable can take its value from a ConfigMap key with valueFrom:

env:
  - name: COLOR
    valueFrom:
      configMapKeyRef:
        name: app-config
        key: COLOR

The same works for Secrets with secretKeyRef. The ConfigMap must exist in the same namespace as the Pod.

Check what the container sees by running env inside it:

kubectl exec app -- env

Both GREETING=hello and COLOR=blue appear in the list.

Challenge

Medium

Create a ConfigMap named app-config with COLOR set to blue. Then open pod.yaml from the file tree and add an environment variable COLOR that takes its value from the COLOR key of app-config, save it, apply it, and run env inside the app Pod to confirm COLOR=blue.

Try it yourself

Terminal