Multistage Docker Builds

So recently I was working on a relatively small Golang microservice. It consumed ZeroMQ streams, performed some calculations on the timeseries data & exposed standarized data via a web API.

I used goczmq as a golang interface to the CZMQ API. Looking at the cgo tags, goczmq depends on following libraries.

These are all the dependencies I needed for my app. Hence, my initial Dockerfile was relatively straightforward.


FROM golang:1.16 as base
RUN apt-get update -qq && \
    apt-get install -qq --yes --no-install-recommends \
      build-essential \
      libczmq-dev \
      libzmq3-dev \
      libsodium-dev
WORKDIR /go/src/app
COPY . .
RUN go get -d -v ./... 
RUN go install -v ./...
CMD ["app"]

While it did the job, the resulting docker image was huge (~1.4GB). The compressed docker image was too around ~500MB. It seemed quite a lot, when the app itself had only 2 package dependencies.

go.mod


require (
  github.com/sirupsen/logrus v1.8.1
  github.com/zeromq/goczmq v0.0.0-20190622112907-4715d4da6d4b
)

Certainly, it was not ideal.

To tackle this, I switched to a multistage build approach. The idea was to:

use golang docker image to prepare the final build.
throw that build on a lightweight base image (debian:buster-slim in this case) for final execution.

With this approach, my final Dockerfile looked as follows:


# syntax=docker/dockerfile:1

FROM golang:1.16 as base
RUN apt-get update -qq && \
  apt-get install -qq --yes --no-install-recommends \
    build-essential \
    libczmq-dev \
    libzmq3-dev \
    libsodium-dev

WORKDIR /go/src/app
COPY . .
RUN go get -d -v ./...
RUN go build -o app ./... 

# ---- Release ----
FROM debian:buster-slim AS release
RUN apt-get update -qq && \
  apt-get install -qq --yes --no-install-recommends libczmq-dev
COPY --from=build /go/src/app/app ./
CMD ["./app"]

The image final size came down to 137MB with compressed size of ~40MB.