How do you implement health checks in Docker and why are they important for orchestration?

The HEALTHCHECK instruction tells Docker how to test if a container is working correctly. Without it, Docker considers a container healthy as soon as the process starts — even if the app inside has crashed.

HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
  CMD curl -f http://localhost:8080/health || exit 1

In Kubernetes, this is replaced by Liveness and Readiness probes. In Docker Compose or standalone Docker, HEALTHCHECK is critical for orchestration tools to know whether to send traffic to a container.