Docker multistage example.Dockerfile

# We add as builder to name our build stage. This is needed so that our second build can refer to it
FROM golang:1.15 as builder
LABEL maintainer="PercyBolmer@medium"

#ARG is used during the Image build
ARG port=8080
# Assign Environment variabel PORT the value of port. The user running the container can then override this with the -e flag
ENV PORT=${port}

RUN mkdir /app
COPY main.go /app
WORKDIR /app

RUN go build -o helloer .

EXPOSE ${PORT}


# Build a second Image based on our first Image, but only copy our needed files
# Removing all necessary files, commands etc is not only saving memory, but
# also good for security reasons.
FROM scratch
# copy the compiled binary named helloer
COPY --from=builder /app/helloer .

# arguments that can be overridden
CMD [ "./helloer"]