What are Kubernetes Init Containers?

Question

Accepted Answer

**Init Containers** — run-to-completion containers that execute before the main containers start.

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 1
  template:
    spec:
      initContainers:
      - name: wait-for-db
        image: busybox:1.36
        command: ["sh", "-c", "until nc -z postgres-service 5432; do sleep 2; done"]
      - name: init-migrations
        image: myapp:latest
        command: ["python", "manage.py", "migrate"]
        env:
        - name: DATABASE_URL
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: url
      - name: load-config
        image: busybox:1.36
        command:
        - sh
        - -c
        - |-
          wget -O /config/app.conf https://config-server/app.conf
          echo "Config loaded"
        volumeMounts:
        - name: config
          mountPath: /config
      containers:
      - name: app
        image: myapp:latest
        volumeMounts:
        - name: config
          mountPath: /config
      volumes:
      - name: config
        emptyDir: {}
```

**Use cases:**
- Wait for dependencies (DB, cache).
- Database migrations.
- Configuration download.
- Schema initialization.

**Behavior:**
- Run sequentially in order.
- Must complete successfully.
- Restart on failure (backoff).

DevOps: What are Kubernetes Init Containers?