112 lines
3.3 KiB
Markdown
112 lines
3.3 KiB
Markdown
# Dockerfile for Go
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Each time I start a new Go project, I repeat many steps. Like set up
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`.gitignore`, CI configs, Dockerfile, ...
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So I decide to have a baseline Dockerfile like this:
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```Dockerfile
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FROM golang:1.22.0-bookworm as builder
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RUN go install golang.org/dl/go1.22.0@latest \
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&& go1.22.0 download
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WORKDIR /build
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COPY go.mod .
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COPY go.sum .
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COPY vendor .
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COPY . .
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RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath -ldflags="-s -w" .
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FROM gcr.io/distroless/base-debian12
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COPY --from=builder /build/app /app
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ENTRYPOINT ["/app"]
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```
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I use
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[multi-stage build](https://docs.docker.com/develop/develop-images/multistage-build/)
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to keep my image size small. First stage is
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[Go official image](https://hub.docker.com/_/golang), second stage is
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[Distroless](https://github.com/GoogleContainerTools/distroless).
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Before Distroless, I use
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[Alpine official image](https://hub.docker.com/_/alpine), There is a whole
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discussion on the Internet to choose which is the best base image for Go. After
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reading some blogs, I discover Distroless as a small and secure base image. So I
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stick with it for a while.
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Also, remember to match Distroless Debian version with Go official image Debian
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version.
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```Dockerfile
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FROM golang:1.22.0-bookworm as builder
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```
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This is Go image I use as a build stage. This can be official Go image or custom
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image is required in some companies.
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```Dockerfile
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RUN go install golang.org/dl/go1.22.0@latest \
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&& go1.22.0 download
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```
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This is optional. In my case, my company is slow to update Go image so I use
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this trick to install latest Go version.
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```Dockerfile
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WORKDIR /build
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COPY go.mod .
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COPY go.sum .
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COPY vendor .
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COPY . .
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```
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I use `/build` to emphasize that I am building something in that directory.
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The 4 `COPY` lines are familiar if you use Go enough. First is `go.mod` and
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`go.sum` because it defines Go modules. The second is `vendor`, this is optional
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but I use it because I don't want each time I build Dockerfile, I need to
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redownload Go modules.
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```Dockerfile
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RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GOAMD64=v3 go build -o ./app -tags timetzdata -trimpath -ldflags="-s -w" .
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```
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This is where I build Go program.
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- `CGO_ENABLED=0` because I don't want to mess with C libraries.
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- `GOOS=linux GOARCH=amd64` is easy to explain, Linux with x86-64.
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- `GOAMD64=v3` is new since [Go 1.18](https://go.dev/doc/go1.18#amd64), I use v3
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because I read about AMD64 version in
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[Arch Linux rfcs](https://gitlab.archlinux.org/archlinux/rfcs/-/blob/master/rfcs/0002-march.rst).
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TLDR's newer computers are already x86-64-v3.
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- `-tags timetzdata` to embed timezone database in case base image does not
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have.
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- `-trimpath` to support reproduce build.
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- `-ldflags="-s -w"` to strip debugging information.
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Also there are some experiment:
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- `GOMEMLIMIT=1024MiB`: soft memory limit.
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```Dockerfile
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FROM gcr.io/distroless/base-debian12
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COPY --from=builder /build/app /app
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ENTRYPOINT ["/app"]
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```
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Finally, I copy `app` to Distroless base image.
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## Thanks
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- [How to start a Go project in 2023](https://boyter.org/posts/how-to-start-go-project-2023/)
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- [Shrink your Go binaries with this one weird trick](https://words.filippo.io/shrink-your-go-binaries-with-this-one-weird-trick/)
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- [GOMEMLIMIT is a game changer for high-memory applications](https://weaviate.io/blog/gomemlimit-a-game-changer-for-high-memory-applications)
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