Docker health checks for container orchestration

Container orchestrators can't determine if the app inside is actually healthy. Container is running but app has crashed or is unresponsive.

Add HEALTHCHECK to Dockerfile: HEALTHCHECK --interval=30s --timeout=10s --retries=3 CMD curl -f http://localhost:3000/health || exit 1. Health endpoint should check: app responding, DB connected, critical deps reachable. Docker Compose: use depends_on with condition: service_healthy. Kubernetes: use readinessProbe and livenessProbe separately.

A process can be running but deadlocked or unable to serve. Health checks let orchestrators detect this and restart or stop routing traffic.