Build a Docker image (multi-arch)

This workflows builds a Docker image for x86 and ARM, and deploys it to a server.

It uses BuildJet for the ARM build, since GitHub currently does not offer ARM runners and emulation is very slow.

.github/workflows/build.yml

name: 'Build and publish'

on:
  workflow_dispatch:
    # Allows to manually run the workflow from GitHub's UI
  schedule:
    # Rebuilds the image automatically every day,
    # to ensure it stays up-to-date and secure
    - cron: '0 8 * * *'
  push:
    branches:
      - 'main'

env:
  IMAGE_NAME: ghcr.io/${{ github.repository }}

jobs:
  build:
    strategy:
      fail-fast: false
      matrix:
        arch: [x86, arm]
    runs-on: ${{ matrix.arch == 'arm' && 'buildjet-2vcpu-ubuntu-2204-arm' || 'ubuntu-latest' }}
    name: Build ${{ matrix.arch == 'arm' && 'ARM' || matrix.arch }} image
    permissions:
      contents: read
      packages: write
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Calculate short form of current git commit
        id: vars
        run: echo "sha_short=$(git rev-parse --short HEAD)" >> "$GITHUB_OUTPUT"

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Login to GitHub Container Registry
        uses: docker/login-action@v2
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Build and push by digest
        id: build
        uses: docker/build-push-action@v4
        with:
          context: .
          platforms: ${{ matrix.arch }}
          outputs: type=image,name=${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=true
          cache-from: type=registry,ref=ghcr.io/${{ env.IMAGE_NAME }}-buildcache:${{ matrix.arch }}
          cache-to: type=registry,ref=ghcr.io/${{ env.IMAGE_NAME }}-buildcache:${{ matrix.arch }},mode=max

      - 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@v3
        with:
          name: digests
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    runs-on: ubuntu-latest
    name: 'Merge into a single manifest'
    needs: build
    permissions:
      packages: write
    steps:
      - name: Download digests
        uses: actions/download-artifact@v3
        with:
          name: digests
          path: /tmp/digests

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Docker meta
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: ${{ env.IMAGE_NAME }}
          tags: |
            type=sha,prefix=git-
            type=raw,value=latest,enable={{is_default_branch}}

      - name: Login to GitHub Container Registry
        uses: docker/login-action@v2
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - 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.IMAGE_NAME }}@sha256:%s ' *)

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

  deploy:
    runs-on: ubuntu-latest
    name: 'Deploy'
    needs: merge
    permissions:
      contents: read
    steps:
      - name: Checkout
        uses: actions/checkout@v3

      - name: Calculate short form of current git commit
        id: vars
        run: echo "sha_short=$(git rev-parse --short HEAD)" >> "$GITHUB_OUTPUT"

      - name: Replace variables in stack file
        env:
          IMAGE_TAG: git-${{ steps.vars.outputs.sha_short }}
        run: >
          sed -e "s \${IMAGE_TAG} $IMAGE_TAG " \
              -i .github/workflows/deploy/stack.yml
          cat .github/workflows/deploy/stack.yml

      - name: Trigger deployment
        env:
          API_KEY: ${{ secrets.StackSparkApiKey }}
          STACKSPARK_HOST: ${{ secrets.StackSparkHost }}
          STACK_NAME: stackspark
        run: >
          curl --fail -H "X-API-Key: $API_KEY" --data-binary "@.github/workflows/deploy/stack.yml" https://$STACKSPARK_HOST/deploy?stackName=$STACK_NAME