What is a Docker healthcheck and how does it differ from a liveness probe?

Both Docker healthchecks and Kubernetes liveness/readiness probes check container health, but they operate in different contexts with different consequences. Docker HEALTHCHECK (Dockerfile/Compose): runs a command inside the container periodically; updates the container's health status (healthy/unhealthy/starting); in Docker Swarm, unhealthy tasks are replaced; Docker Compose respects health status for depends_on with condition: service_healthy. Example: HEALTHCHECK --interval=30s --timeout=5s --retries=3 CMD curl -f http://localhost:3000/health || exit 1. Kubernetes Probes: (1) Liveness probe: determines if the container is running; if it fails, Kubernetes kills and restarts the container — for detecting deadlocks; (2) Readiness probe: determines if the container is ready to serve traffic; if it fails, Kubernetes removes the Pod from Service endpoints (stops sending traffic) but doesn't restart it — for slow startup or temporary unavailability; (3) Startup probe: protects slow-starting containers from liveness probe failures during initialization. Docker healthchecks are simpler; Kubernetes probes are more powerful and fine-grained. In Kubernetes deployments, define both liveness and readiness probes at the Pod spec level, not in the Dockerfile (though Docker healthcheck metadata can inform K8s configuration).