<!doctype html><metacharset=utf-8><metaname=viewportcontent="width=device-width,initial-scale=1"><linkrel=stylesheethref=https://cdnjs.cloudflare.com/ajax/libs/github-markdown-css/5.1.0/github-markdown-dark.css><style>.markdown-body{box-sizing:border-box;min-width:200px;max-width:980px;margin:0auto;padding:45px}@media(max-width:767px){.markdown-body{padding:15px}}</style><bodyclass=markdown-body><ahref=index>Index</a><h1><aid=user-content-dockerfile-for-goclass=anchoraria-hidden=truehref=#dockerfile-for-go><spanaria-hidden=trueclass="octicon octicon-link"></span></a>Dockerfile for Go</h1><p>Each time I start a new Go project, I repeat many steps.
Like set up <code>.gitignore</code>, CI configs, Dockerfile, ...<p>So I decide to have a baseline Dockerfile like this:<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>FROM</span> golang:1.19-bullseye as builder
<spanclass=pl-k>ENTRYPOINT</span> [<spanclass=pl-s>"/app"</span>]</pre></div><p>I use <ahref=https://docs.docker.com/develop/develop-images/multistage-build/rel=nofollow>multi-stage build</a> to keep my image size small.
First stage is <ahref=https://hub.docker.com/_/golangrel=nofollow>Go official image</a>,
second stage is <ahref=https://github.com/GoogleContainerTools/distroless>Distroless</a>.<p>Before Distroless, I use <ahref=https://hub.docker.com/_/alpinerel=nofollow>Alpine official image</a>,
There is a whole discussion on the Internet to choose which is the best base image for Go.
After reading some blogs, I discover Distroless as a small and secure base image.
So I stick with it for a while.<p>Also, remember to match Distroless Debian version with Go official image Debian version.<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>FROM</span> golang:1.19-bullseye as builder</pre></div><p>This is Go image I use as a build stage.
This can be official Go image or custom image is required in some companies.<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>RUN</span> go install golang.org/dl/go1.19@latest \
&& go1.19 download</pre></div><p>This is optional.
In my case, my company is slow to update Go image so I use this trick to install latest Go version.<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>WORKDIR</span> /build
<spanclass=pl-k>COPY</span> . .</pre></div><p>I use <code>/build</code> to emphasize that I am building something in that directory.<p>The 4 <code>COPY</code> lines are familiar if you use Go enough.
First is <code>go.mod</code> and <code>go.sum</code> because it defines Go modules.
The second is <code>vendor</code>, this is optional but I use it because I don't want each time I build Dockerfile, I need to redownload Go modules.<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>RUN</span> CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath .</pre></div><p>This is where I build Go program.<p><code>CGO_ENABLED=0</code> because I don't want to mess with C libraries.
<code>GOOS=linux GOARCH=amd64</code> is easy to explain, Linux with x86-64.
<code>GOAMD64=v3</code> is new since <ahref=https://go.dev/doc/go1.18#amd64rel=nofollow>Go 1.18</a>,
I use v3 because I read about AMD64 version in <ahref=https://gitlab.archlinux.org/archlinux/rfcs/-/blob/master/rfcs/0002-march.rstrel=nofollow>Arch Linux rfcs</a>. TLDR's newer computers are already x86-64-v3.<p><code>-tags timetzdata</code> to embed timezone database incase base image does not have.
<code>-trimpath</code> to support reproduce build.<divclass="highlight highlight-source-dockerfile"><pre><spanclass=pl-k>FROM</span> gcr.io/distroless/base-debian11
<spanclass=pl-k>ENTRYPOINT</span> [<spanclass=pl-s>"/app"</span>]</pre></div><p>Finally, I copy <code>app</code> to Distroless base image.</p><ahref=mailto:hauvipapro+posts@gmail.com>Feel free to ask me via email</a>
