Multi-platform Docker images with GoReleaser and GitHub Actions

GoReleaser v0.148.0 is out, and with it, the ability to release multi-platform Docker images, a.k.a. Docker Manifests.

In this guide we’ll explore how to use it with GitHub Actions, and how GoReleaser releases itself in this way.

PS: You will need GoReleaser version 0.152.0 or later for this guide to work properly.

An example project#

I created an example project showing with all the code needed for everything to work. You can check it out here.

A simple `main.go`#

For our example, we’ll have a very simple main.go file:

// main.go
package main

import (
	"fmt"
	"runtime"
)

var version = "dev"

func main() {
	fmt.Println("example", version, runtime.GOOS, runtime.GOARCH)
}

Our mighty `Dockerfile`#

GoReleaser builds Docker images by copying the previously built binaries to the images (instead of building the binary inside Docker itself). This guarantees that the binary inside the image and the one you download from the releases page is the same.

Our very basic Dockerfile looks like this:

# Dockerfile
FROM alpine
COPY example /usr/bin/example
ENTRYPOINT ["/usr/bin/example"]

To account for multiple platforms, we either create several dockerfiles, or use the --platform build flag. We’ll use the second approach in our example.

We can test it without GoReleaser by running:

GOOS=linux GOARCH=amd64 go build -o example .
docker buildx build -t testimage:amd64 . --platform=linux/amd64

GOOS=linux GOARCH=arm64 go build -o example .
docker buildx build -t testimage:arm64v8 . --platform=linux/arm64/v8

With that in place, let’s check our GoReleaser config file.

Our very own `.goreleaser.yml`#

Our GoReleaser config file is very simple:

One item in the builds section which will build for multiple platforms;
Two items in the dockers section, building one image for amd64 and another for arm64;
One item in the new docker_manifests section, tying together the two images in a single manifest.

It looks like this:

# .goreleaser.yml
project_name: example
builds:
  - env: [CGO_ENABLED=0]
    goos:
      - linux
      - windows
      - darwin
    goarch:
      - amd64
      - arm64
dockers:
- image_templates: ["ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:{{ .Version }}-amd64"]
  binaries: [example]
  dockerfile: Dockerfile
  use_buildx: true
  build_flag_templates:
  - --platform=linux/amd64
  - --label=org.opencontainers.image.title={{ .ProjectName }}
  - --label=org.opencontainers.image.description={{ .ProjectName }}
  - --label=org.opencontainers.image.url=https://github.com/caarlos0/goreleaser-docker-manifest-actions-example
  - --label=org.opencontainers.image.source=https://github.com/caarlos0/goreleaser-docker-manifest-actions-example
  - --label=org.opencontainers.image.version={{ .Version }}
  - --label=org.opencontainers.image.created={{ time "2006-01-02T15:04:05Z07:00" }}
  - --label=org.opencontainers.image.revision={{ .FullCommit }}
  - --label=org.opencontainers.image.licenses=MIT
- image_templates: ["ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:{{ .Version }}-arm64v8"]
  binaries: [example]
  goarch: arm64
  dockerfile: Dockerfile
  use_buildx: true
  build_flag_templates:
  - --platform=linux/arm64/v8
  - --label=org.opencontainers.image.title={{ .ProjectName }}
  - --label=org.opencontainers.image.description={{ .ProjectName }}
  - --label=org.opencontainers.image.url=https://github.com/caarlos0/goreleaser-docker-manifest-actions-example
  - --label=org.opencontainers.image.source=https://github.com/caarlos0/goreleaser-docker-manifest-actions-example
  - --label=org.opencontainers.image.version={{ .Version }}
  - --label=org.opencontainers.image.created={{ time "2006-01-02T15:04:05Z07:00" }}
  - --label=org.opencontainers.image.revision={{ .FullCommit }}
  - --label=org.opencontainers.image.licenses=MIT
docker_manifests:
- name_template: ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:{{ .Version }}
  image_templates:
  - ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:{{ .Version }}-amd64
  - ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:{{ .Version }}-arm64v8

You can check more options for builds, docker and docker manifests on GoReleaser’s website.

The labels added to the images are optional, but in the specific case of ghcr.io, they allows GitHub to know which image is built from which repository and other metadata.

We can now verify this locally with:

goreleaser release --snapshot --rm-dist

GoReleaser will use defaults for a lot of things, you can check the full config (with the defaults) in at dist/config.yaml.

GitHub Actions#

Here we pretty much copy what’s already in GitHub Actions section in the GoReleaser’s website:

# .github/workflows/goreleaser.yml
name: goreleaser

on:
  pull_request:
  push:

jobs:
  goreleaser:
    runs-on: ubuntu-latest
    env:
      DOCKER_CLI_EXPERIMENTAL: "enabled"
    steps:
      -
        name: Checkout
        uses: actions/checkout@v2
        with:
          fetch-depth: 0
      -
        name: Set up QEMU
        uses: docker/setup-qemu-action@v1
      -
        name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v1
      -
        name: Docker Login
        uses: docker/login-action@v1
        with:
          registry: ghcr.io
          username: ${{ github.repository_owner }}
          password: ${{ secrets.GH_PAT }}
      -
        name: Set up Go
        uses: actions/setup-go@v2
        with:
          go-version: 1.15
      -
        name: Run GoReleaser
        uses: goreleaser/goreleaser-action@v2
        if: startsWith(github.ref, 'refs/tags/')
        with:
          version: latest
          args: release --rm-dist
        env:
          GITHUB_TOKEN: ${{ secrets.GH_PAT }}
      -
        name: Clear
        if: always()
        run: |
          rm -f ${HOME}/.docker/config.json

Important things to notice#

We need to set DOCKER_CLI_EXPERIMENTAL=enabled for the docker manifest command to work;
We need to setup qemu and buildx in order to build Docker images in platforms other than linux/amd64 using docker buildx build;
We need to login into the GitHub Container Registry with a Personal Access Token (PAT), since the default GITHUB_TOKEN does not have enough permissions.

And that’s pretty much it!

Releasing#

Now, we just need to push a tag, sit back, relax and watch the GoReleaser Action do everything.

In the end, you should have a release more or less like this:

GitHub Release - the changelog, assets and our multi-platform Docker image

You should also be able to see that the image is in fact multi-platform in the container registry:

GitHub Container Registry showing both OS/Arch combinations we provided.

We can now run our image:

$ docker run --rm --platform linux/amd64 \
	ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:1.0.2
example 1.0.2 linux amd64

We can also test the arm64 image:

$ docker run --rm --platform linux/arm64/v8 \
	ghcr.io/caarlos0/goreleaser-docker-manifest-actions-example:1.0.2
example 1.0.2 linux arm64

It works! 🎉

That’s it!#

That’s it! I hope this is useful somehow.

Don’t forget to check out GoReleaser’s documentation for more details. Also make sure to take a look at Docker’s manifest documentation.

Special Thanks#

@CrazyMax for the review;

Updates#

Jan 04, 2021: using buildx and setting use_buildx on the Docker config and using docker/setup-qemu-action;
Dec 29, 2020: using --platform instead of ARCH build arg, added more docker run examples;