Golang Docker HEALTHCHECK

Simple HEALTHCHECK solution for Go Docker container

The Problem

We usually add a HEALTHCHECK instruction to our Dockerfiles and then check their status with the docker inspect command. Usually the health check performs an http request to server endpoint, and if it succeeds the server is considered in healthy condition. In Linux-based containers we do it with the curl or wget command. The problem is that in containers built from scratch there are no such commands.

Solution

We decided to add a new package that contains several lines...

_, err := http.Get(fmt.Sprintf("http://127.0.0.1:%s/health", os.Getenv("PORT")))
if err != nil {
	os.Exit(1)
}

... and then build the package as another executable, and add the HEALTHCHECK instruction to the Dockerfile

# Stage 1: Use a builder as first stage
...
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o /build/server
RUN CGO_ENABLED=0 GOOS=linux go build -a -installsuffix cgo -o /build/healthcheck "github.com/GRS-Service-GmbH/golang-docker-healthcheck/healthcheck"

# Stage 2: Create release image from scratch and copy both artifacts from the builder stage
FROM scratch

COPY --from=builder /build/server ./server
COPY --from=builder /build/healthcheck ./healthcheck

ENV PORT=8000
EXPOSE $PORT

HEALTHCHECK --interval=1s --timeout=1s --start-period=2s --retries=3 CMD [ "/healthcheck" ]

ENTRYPOINT [ "/server" ]

So we now have two executables in the docker container: the server and the healthcheck utility.

Conclusion

In this repository we demonstrated a health-check for a server implemented in Go, for a docker container built from scratch.