CKAD field manual

k8s sidecar YAML example

Same Pod, extra container. Init must finish. A sidecar stays up and shares volumes.

Init + app

apiVersion: v1
kind: Pod
metadata:
  name: web
spec:
  initContainers:
    - name: fetch
      image: busybox:1.36
      command: ["sh", "-c", "echo hi > /data/index.html"]
      volumeMounts:
        - name: html
          mountPath: /data
  containers:
    - name: web
      image: nginx:1.27
      volumeMounts:
        - name: html
          mountPath: /usr/share/nginx/html
  volumes:
    - name: html
      emptyDir: {}

Classic sidecar

spec:
  containers:
    - name: app
      image: nginx:1.27
      volumeMounts:
        - name: logs
          mountPath: /var/log/nginx
    - name: shipper
      image: busybox:1.36
      command: ["sh", "-c", "tail -F /var/log/nginx/access.log"]
      volumeMounts:
        - name: logs
          mountPath: /var/log/nginx
  volumes:
    - name: logs
      emptyDir: {}

Native sidecar

spec:
  initContainers:
    - name: shipper
      image: busybox:1.36
      restartPolicy: Always
      command: ["sh", "-c", "tail -F /var/log/app.log"]
      volumeMounts:
        - name: logs
          mountPath: /var/log
  containers:
    - name: app
      image: nginx:1.27
      volumeMounts:
        - name: logs
          mountPath: /var/log
  volumes:
    - name: logs
      emptyDir: {}

Fields

initContainers: Run to completion, in order, before app containers. A failing init blocks the Pod.
restartPolicy: Always on an initContainer = native sidecar. It stays up with the app.
emptyDir: How the containers share files. Same volume name on every mount.

Watch

Init containers run to completion, in order, before app containers start. A failing init blocks the Pod.
Classic sidecar = second item in containers[]. Native sidecar = initContainers[] + restartPolicy: Always.
Share files with emptyDir. Same volume name in every volumeMounts.

Official docs Init containers Sidecar containers

Practice these objects on a live cluster →