Sidecar Containers

As of kubernetes 1.33, sidecar containers are natively supported. This allows sidecar containers to follow a defined lifecycle relative to the main containers in the pod, without requiring entrypoint hacks. https://kubernetes.io/docs/concepts/workloads/pods/sidecar-containers/

How Native Sidecars Work

• Declared using the restartPolicy: Always field inside the initContainers block.

• Kubernetes treats such containers as sidecars, ensuring they:

  • Start before main containers.
  • Run alongside them.
  • Shut down after the main containers complete

• Example sidecar manifest:

apiVersion: v1
kind: Pod
metadata:
  name: sidecar-example
spec:
  initContainers:
    - name: sidecar-logger
      image: busybox:1.31
      restartPolicy: Always
      command: ["sh", "-c", "while true; do echo Sidecar running; sleep 10; done"]
  containers:
    - name: main-app
      image: busybox:1.31
      command: ["sh", "-c", "echo Main app starting; sleep 60"]

• In this setup:
  • The sidecar-logger container behaves like a sidecar, though declared in initContainers.
  • It uses restartPolicy: Always to stay alive throughout the Pod lifecycle.
  • Kubernetes starts the sidecar first, waits for readiness, then starts the main app.