Multi-platform image with GitHub Actions

もくじ

You can build multi-platform images using the platforms option, as shown in the following example:

メモ

name: ci

on:
  push:

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Build and push
        uses: docker/build-push-action@v6
        with:
          platforms: linux/amd64,linux/arm64
          push: true
          tags: user/app:latest

Build and load multi-platform images

The default Docker setup for GitHub Actions runners does not support loading multi-platform images to the local image store of the runner after building them. To load a multi-platform image, you need to enable the containerd image store option for the Docker Engine.

There is no way to configure the default Docker setup in the GitHub Actions runners directly, but you can use docker/setup-docker-action to customize the Docker Engine and CLI settings for a job.

The following example workflow enables the containerd image store, builds a multi-platform image, and loads the results into the GitHub runner's local image store.

name: ci

on:
  push:

jobs:
  docker:
    runs-on: ubuntu-latest
    steps:
      - name: Set up Docker
        uses: docker/setup-docker-action@v4
        with:
          daemon-config: |
            {
              "debug": true,
              "features": {
                "containerd-snapshotter": true
              }
            }            

      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Build and push
        uses: docker/build-push-action@v6
        with:
          platforms: linux/amd64,linux/arm64
          load: true
          tags: user/app:latest

Distribute build across multiple runners

In the previous example, each platform is built on the same runner which can take a long time depending on the number of platforms and your Dockerfile.

To solve this issue you can use a matrix strategy to distribute the build for each platform across multiple runners and create manifest list using the buildx imagetools create command.

The following workflow will build the image for each platform on a dedicated runner using a matrix strategy and push by digest. Then, the merge job will create a manifest list and push it to Docker Hub.

This example also uses the metadata action to set tags and labels.

name: ci

on:
  push:

env:
  REGISTRY_IMAGE: user/app

jobs:
  build:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        platform:
          - linux/amd64
          - linux/arm/v6
          - linux/arm/v7
          - linux/arm64
    steps:
      - name: Prepare
        run: |
          platform=${{ matrix.platform }}
          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV          

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY_IMAGE }}

      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Build and push by digest
        id: build
        uses: docker/build-push-action@v6
        with:
          platforms: ${{ matrix.platform }}
          labels: ${{ steps.meta.outputs.labels }}
          outputs: type=image,name=${{ env.REGISTRY_IMAGE }},push-by-digest=true,name-canonical=true,push=true

      - name: Export digest
        run: |
          mkdir -p /tmp/digests
          digest="${{ steps.build.outputs.digest }}"
          touch "/tmp/digests/${digest#sha256:}"          

      - name: Upload digest
        uses: actions/upload-artifact@v4
        with:
          name: digests-${{ env.PLATFORM_PAIR }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    runs-on: ubuntu-latest
    needs:
      - build
    steps:
      - name: Download digests
        uses: actions/download-artifact@v4
        with:
          path: /tmp/digests
          pattern: digests-*
          merge-multiple: true

      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY_IMAGE }}

      - name: Create manifest list and push
        working-directory: /tmp/digests
        run: |
          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
            $(printf '${{ env.REGISTRY_IMAGE }}@sha256:%s ' *)          

      - name: Inspect image
        run: |
          docker buildx imagetools inspect ${{ env.REGISTRY_IMAGE }}:${{ steps.meta.outputs.version }}

With Bake

It's also possible to build on multiple runners using Bake, with the bake action.

You can find a live example in this GitHub repository.

The following example achieves the same results as described in the previous section.

variable "DEFAULT_TAG" {
  default = "app:local"
}

// Special target: https://github.com/docker/metadata-action#bake-definition
target "docker-metadata-action" {
  tags = ["${DEFAULT_TAG}"]
}

// Default target if none specified
group "default" {
  targets = ["image-local"]
}

target "image" {
  inherits = ["docker-metadata-action"]
}

target "image-local" {
  inherits = ["image"]
  output = ["type=docker"]
}

target "image-all" {
  inherits = ["image"]
  platforms = [
    "linux/amd64",
    "linux/arm/v6",
    "linux/arm/v7",
    "linux/arm64"
  ]
}
name: ci

on:
  push:

env:
  REGISTRY_IMAGE: user/app

jobs:
  prepare:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.platforms.outputs.matrix }}
    steps:
      - name: Checkout
        uses: actions/checkout@v4

      - name: Create matrix
        id: platforms
        run: |
          echo "matrix=$(docker buildx bake image-all --print | jq -cr '.target."image-all".platforms')" >>${GITHUB_OUTPUT}          

      - name: Show matrix
        run: |
          echo ${{ steps.platforms.outputs.matrix }}          

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY_IMAGE }}

      - name: Rename meta bake definition file
        run: |
          mv "${{ steps.meta.outputs.bake-file }}" "/tmp/bake-meta.json"          

      - name: Upload meta bake definition
        uses: actions/upload-artifact@v4
        with:
          name: bake-meta
          path: /tmp/bake-meta.json
          if-no-files-found: error
          retention-days: 1

  build:
    runs-on: ubuntu-latest
    needs:
      - prepare
    strategy:
      fail-fast: false
      matrix:
        platform: ${{ fromJson(needs.prepare.outputs.matrix) }}
    steps:
      - name: Prepare
        run: |
          platform=${{ matrix.platform }}
          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV          

      - name: Checkout
        uses: actions/checkout@v4

      - name: Download meta bake definition
        uses: actions/download-artifact@v4
        with:
          name: bake-meta
          path: /tmp

      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Build
        id: bake
        uses: docker/bake-action@v5
        with:
          files: |
            ./docker-bake.hcl
            /tmp/bake-meta.json            
          targets: image
          set: |
            *.tags=
            *.platform=${{ matrix.platform }}
            *.output=type=image,"name=${{ env.REGISTRY_IMAGE }}",push-by-digest=true,name-canonical=true,push=true            

      - name: Export digest
        run: |
          mkdir -p /tmp/digests
          digest="${{ fromJSON(steps.bake.outputs.metadata).image['containerimage.digest'] }}"
          touch "/tmp/digests/${digest#sha256:}"          

      - name: Upload digest
        uses: actions/upload-artifact@v4
        with:
          name: digests-${{ env.PLATFORM_PAIR }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    runs-on: ubuntu-latest
    needs:
      - build
    steps:
      - name: Download meta bake definition
        uses: actions/download-artifact@v4
        with:
          name: bake-meta
          path: /tmp

      - name: Download digests
        uses: actions/download-artifact@v4
        with:
          path: /tmp/digests
          pattern: digests-*
          merge-multiple: true

      - name: Login to DockerHub
        uses: docker/login-action@v3
        with:
          username: ${{ vars.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Create manifest list and push
        working-directory: /tmp/digests
        run: |
          docker buildx imagetools create $(jq -cr '.target."docker-metadata-action".tags | map(select(startswith("${{ env.REGISTRY_IMAGE }}")) | "-t " + .) | join(" ")' /tmp/bake-meta.json) \
            $(printf '${{ env.REGISTRY_IMAGE }}@sha256:%s ' *)          

      - name: Inspect image
        run: |
          docker buildx imagetools inspect ${{ env.REGISTRY_IMAGE }}:$(jq -r '.target."docker-metadata-action".args.DOCKER_META_VERSION' /tmp/bake-meta.json)