Distribute build across multiple runners

.github/workflows/docker-publish.yml

@@ -1,9 +1,9 @@
 name: Docker
 
 env:
-  REPO_NAME: ${{ github.event.repository.name }}
   # github.repository as <account>/<repo>
-  IMAGE_NAME: ${{ github.repository }}
+  DOCKERHUB_REPO: ${{ github.repository }}
+  GHCR_REPO: ghcr.io/${{ github.repository }}
 
 on:
   pull_request:
@@ -25,61 +25,79 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - os: ubuntu-24.04
+            platform: linux/amd64
+          - os: ubuntu-24.04-arm
+            platform: linux/arm64
+
     permissions:
       contents: read
       packages: write
-      # This is used to complete the identity challenge
-      # with sigstore/fulcio when running outside of PRs.
-      id-token: write
 
     steps:
-      - name: Checkout repository
-        uses: actions/checkout@v4
+      - name: Prepare
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
 
-      # Install the cosign tool except on PR
-      # https://github.com/sigstore/cosign-installer
-      - name: Install cosign
-        if: github.event_name != 'pull_request'
-        uses: sigstore/cosign-installer@v3
-
-      - name: Set up QEMU
-        uses: docker/setup-qemu-action@v3
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: |
+            ${{ env.DOCKERHUB_REPO }}
+            ${{ env.GHCR_REPO }}
 
-      - name: Setup Docker buildx
-        uses: docker/setup-buildx-action@v3
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
-      # Login against a Docker registry except on PR
-      # https://github.com/docker/login-action
       - name: Log in to Docker Hub
         if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
 
-      # Login against a Docker registry except on PR
-      # https://github.com/docker/login-action
-      - name: Log in to the Container registry
+      - name: Login to GHCR
         if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
-      # Extract metadata (tags, labels) for Docker
-      # https://github.com/docker/metadata-action
-      - name: Extract Docker metadata
-        id: meta
-        uses: docker/metadata-action@v5
+      - name: Setup Docker buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v6
         with:
-          images: |
-            ${{ env.IMAGE_NAME }}
-            ghcr.io/${{ env.IMAGE_NAME }}
+          context: image/
+          platforms: ${{ matrix.platform }}
+          push: ${{ github.event_name != 'pull_request' }}
+          labels: ${{ steps.meta.outputs.labels }}
+          outputs: type=image,"name=${{ env.DOCKERHUB_REPO }},${{ env.GHCR_REPO }}",push-by-digest=true,name-canonical=true,push=true
+
+      - name: Export digest
+        run: |
+          mkdir -p ${{ runner.temp }}/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "${{ runner.temp }}/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error
+          retention-days: 1
 
-      # Build and push Docker image with Buildx (don't push on PR)
-      # https://github.com/docker/build-push-action
       - name: Build and push Docker image
         id: build-and-push
         uses: docker/build-push-action@v6
@@ -94,15 +112,60 @@ jobs:
           cache-from: type=gha
           cache-to: type=gha,mode=max
 
-      # Sign the resulting Docker image digest except on PRs.
-      # This will only write to the public Rekor transparency log when the Docker
-      # repository is public to avoid leaking data.  If you would like to publish
-      # transparency data even for private images, pass --force to cosign below.
-      # https://github.com/sigstore/cosign
-      - name: Sign the published Docker image
-        if: ${{ github.event_name != 'pull_request' }}
-        env:
-          COSIGN_EXPERIMENTAL: "true"
-        # This step uses the identity token to provision an ephemeral certificate
-        # against the sigstore community Fulcio instance.
-        run: echo "${{ steps.meta.outputs.tags }}" | xargs -I {} cosign sign --yes {}@${{ steps.build-and-push.outputs.digest }}
+  merge:
+    runs-on: ubuntu-24.04
+    needs:
+      - build
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: ${{ runner.temp }}/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - name: Login to Docker Hub
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          username: ${{ vars.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Login to GHCR
+        if: github.event_name != 'pull_request'
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_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.DOCKERHUB_REPO }}
+            ${{ env.GHCR_REPO }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+
+      - name: Create manifest list and push
+        if: github.event_name != 'pull_request'
+        working-directory: ${{ runner.temp }}/digests
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.DOCKERHUB_REPO }}@sha256:%s ' *)
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf '${{ env.GHCR_REPO }}@sha256:%s ' *)
+
+      - name: Inspect image
+        if: github.event_name != 'pull_request'
+        run: |
+          docker buildx imagetools inspect ${{ env.DOCKERHUB_REPO }}:${{ steps.meta.outputs.version }}
+          docker buildx imagetools inspect ${{ env.GHCR_REPO }}:${{ steps.meta.outputs.version }}