What are init-containers and sidecar-containers?

In Kubernetes, init containers and sidecar containers are special types of containers that help manage the lifecycle and functionality of a pod.

• Init containers run before the main containers in a pod. They perform preparatory tasks such as data initialization, dependency checks, or environment setup. The main containers start only after all init containers have successfully completed.

• Sidecar containers run alongside the main containers in a pod and extend or complement their functionality. For example, a sidecar can provide logging, proxying, monitoring, or data synchronization.

Example of using an init container:

initContainers:
  - name: init-db
    image: busybox
    command: ['sh', '-c', 'until nslookup database; do echo waiting for db; sleep 2; done;']

Example of a sidecar container for logging:

containers:
  - name: app
    image: myapp
  - name: log-agent
    image: fluentd

Thus, init containers prepare the environment, and sidecar containers extend the application's capabilities.