94 lines
2.8 KiB
Markdown
94 lines
2.8 KiB
Markdown
# Dockerfile for Go
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Each time I start a new Go project, I repeat many steps.
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Like set up `.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:1.20-bullseye as builder
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RUN go install golang.org/dl/go1.20@latest \
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&& go1.20 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 .
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FROM gcr.io/distroless/base-debian11
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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 [multi-stage build](https://docs.docker.com/develop/develop-images/multistage-build/) to keep my image size small.
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First stage is [Go official image](https://hub.docker.com/_/golang),
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second stage is [Distroless](https://github.com/GoogleContainerTools/distroless).
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Before Distroless, I use [Alpine official image](https://hub.docker.com/_/alpine),
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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.
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Also, remember to match Distroless Debian version with Go official image Debian version.
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```Dockerfile
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FROM golang:1.20-bullseye as builder
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```
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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.
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```Dockerfile
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RUN go install golang.org/dl/go1.20@latest \
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&& go1.20 download
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```
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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.
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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.
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First is `go.mod` and `go.sum` because it defines Go modules.
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The second is `vendor`, this is optional but I use it because I don't want each time I build Dockerfile, I need to 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 .
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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),
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I use v3 because I read about AMD64 version in [Arch Linux rfcs](https://gitlab.archlinux.org/archlinux/rfcs/-/blob/master/rfcs/0002-march.rst). TLDR's newer computers are already x86-64-v3.
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`-tags timetzdata` to embed timezone database incase base image does not have.
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`-trimpath` to support reproduce build.
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```Dockerfile
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FROM gcr.io/distroless/base-debian11
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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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