Can you explain what init containers are in the context of container orchestration?

Init containers are special containers in Kubernetes that run before the main containers in a pod. They perform preparatory tasks, such as environment initialization, service availability checks, or configuration loading. Key features of init containers:

• They run sequentially, one after another.
• Each must complete successfully before the next starts.
• If an init container fails, the main container does not start.

Example usage: an init container might wait until a database becomes available before starting the application.

apiVersion: v1
kind: Pod
metadata:
  name: example-pod
spec:
  initContainers:
  - name: wait-for-db
    image: busybox
    command: ['sh', '-c', 'until nc -z db 5432; do echo waiting; sleep 2; done;']
  containers:
  - name: app
    image: myapp:latest

Thus, init containers help ensure that the necessary conditions for the main application are met.