Add a healthcheck to an HTTP service

Approach

Expose a cheap /health endpoint and declare a HEALTHCHECK that calls it with a tool present in the image. In Compose, other services can wait for service_healthy.

Solution

FROM nginx:1.29-alpine
COPY site/ /usr/share/nginx/html/
HEALTHCHECK --interval=10s --timeout=3s --start-period=10s --retries=3 \
  CMD wget -qO- http://127.0.0.1/health || exit 1

Pitfalls

• Using curl in an image that doesn't contain it.
• Health endpoints that check every dependency, marking the app unhealthy during a database blip.
• Expecting plain Docker to restart unhealthy containers; it doesn't (orchestrators do).

Variations

• In distroless images, build a tiny health binary into the image or rely on the orchestrator's HTTP probes.
• Separate liveness and readiness endpoints for Kubernetes.

Further reading: HEALTHCHECK