Docker multistage build for golang create big image

Question

I want to use the multi stage build for my gaoling project, when I build the project locally for linux/windows/Mac I got 12.6 mb of size , I’ve currently small gaoling CLI program.

Now I want to build it with to build from it lightwhigt docker image with the scratch option and build as

I use the following, but when I check the image, I see that the size it 366MB , any idea what am I missing here? It should be less then 20MB…

#build stage
FROM golang:alpine as builder
WORKDIR /go/src/tzf
ADD . /go/src/tzf
RUN CGO_ENABLED=0 go build -ldflags '-extldflags "-static"' -o ova tzf
RUN apk add --no-cache git



FROM golang:alpine 
RUN mkdir /build
ADD . /build/
WORKDIR /build
RUN CGO_ENABLED=0 go build -ldflags '-extldflags "-static"' -o ova tzf
FROM scratch
COPY --from=builder /build/main /app/
WORKDIR /app
CMD [“./ova -v"]

Answer 1

When you build your final image, be careful to copy only the exact files you want to end up in the image. It makes sense here to make your binary be the ENTRYPOINT of the image, since there's literally nothing else you can do with it.

I might make a two-stage pipeline like so:

# size of this stage doesn't matter; use the standard image
FROM golang AS builder
WORKDIR /go/src/tzf
ADD . ./
RUN CGO_ENABLED=0 go build -ldflags '-extldflags "-static"' -o /ova tzf

FROM scratch
# only copy the one file, may as well put it in /
COPY --from=builder /ova /ova
ENTRYPOINT ["/ova"]
# if you want to launch it with default options, you can
# CMD ["-v"]