98 lines
5.0 KiB
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98 lines
5.0 KiB
HTML
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<a href="index">Index</a>
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<h1><a id="user-content-dockerfile-for-go" class="anchor" aria-hidden="true" href="#dockerfile-for-go"><span aria-hidden="true" class="octicon octicon-link"></span></a>Dockerfile for Go</h1>
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<p>Each time I start a new Go project, I repeat many steps.
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Like set up <code>.gitignore</code>, CI configs, Dockerfile, ...</p>
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<p>So I decide to have a baseline Dockerfile like this:</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">FROM</span> golang:1.19-bullseye as builder
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<span class="pl-k">RUN</span> go install golang.org/dl/go1.19@latest \
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&& go1.19 download
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<span class="pl-k">WORKDIR</span> /build
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<span class="pl-k">COPY</span> go.mod .
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<span class="pl-k">COPY</span> go.sum .
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<span class="pl-k">COPY</span> vendor .
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<span class="pl-k">COPY</span> . .
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<span class="pl-k">RUN</span> CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath .
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<span class="pl-k">FROM</span> gcr.io/distroless/base-debian11
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<span class="pl-k">COPY</span> --from=builder /build/app /app
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<span class="pl-k">ENTRYPOINT</span> [<span class="pl-s">"/app"</span>]</pre></div>
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<p>I use <a href="https://docs.docker.com/develop/develop-images/multistage-build/" rel="nofollow">multi-stage build</a> to keep my image size small.
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First stage is <a href="https://hub.docker.com/_/golang" rel="nofollow">Go official image</a>,
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second stage is <a href="https://github.com/GoogleContainerTools/distroless">Distroless</a>.</p>
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<p>Before Distroless, I use <a href="https://hub.docker.com/_/alpine" rel="nofollow">Alpine official image</a>,
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There is a whole discussion on the Internet to choose which is the best base image for Go.
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After reading some blogs, I discover Distroless as a small and secure base image.
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So I stick with it for a while.</p>
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<p>Also, remember to match Distroless Debian version with Go official image Debian version.</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">FROM</span> golang:1.19-bullseye as builder</pre></div>
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<p>This is Go image I use as a build stage.
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This can be official Go image or custom image is required in some companies.</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">RUN</span> go install golang.org/dl/go1.19@latest \
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&& go1.19 download</pre></div>
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<p>This is optional.
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In my case, my company is slow to update Go image so I use this trick to install latest Go version.</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">WORKDIR</span> /build
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<span class="pl-k">COPY</span> go.mod .
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<span class="pl-k">COPY</span> go.sum .
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<span class="pl-k">COPY</span> vendor .
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<span class="pl-k">COPY</span> . .</pre></div>
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<p>I use <code>/build</code> to emphasize that I am building something in that directory.</p>
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<p>The 4 <code>COPY</code> lines are familiar if you use Go enough.
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First is <code>go.mod</code> and <code>go.sum</code> because it defines Go modules.
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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.</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">RUN</span> CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath .</pre></div>
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<p>This is where I build Go program.</p>
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<p><code>CGO_ENABLED=0</code> because I don't want to mess with C libraries.
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<code>GOOS=linux GOARCH=amd64</code> is easy to explain, Linux with x86-64.
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<code>GOAMD64=v3</code> is new since <a href="https://go.dev/doc/go1.18#amd64" rel="nofollow">Go 1.18</a>,
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I use v3 because I read about AMD64 version in <a href="https://gitlab.archlinux.org/archlinux/rfcs/-/blob/master/rfcs/0002-march.rst" rel="nofollow">Arch Linux rfcs</a>. TLDR's newer computers are already x86-64-v3.</p>
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<p><code>-tags timetzdata</code> to embed timezone database incase base image does not have.
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<code>-trimpath</code> to support reproduce build.</p>
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<div class="highlight highlight-source-dockerfile"><pre><span class="pl-k">FROM</span> gcr.io/distroless/base-debian11
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<span class="pl-k">COPY</span> --from=builder /build/app /app
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<span class="pl-k">ENTRYPOINT</span> [<span class="pl-s">"/app"</span>]</pre></div>
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<p>Finally, I copy <code>app</code> to Distroless base image.</p>
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<a href="mailto:hauvipapro+posts@gmail.com"
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>Feel free to ask me via email</a
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>
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<a rel="me" href="https://hachyderm.io/@haunguyen">Mastodon</a>
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