docker: Build arm image using ubuntu-24.04-arm runner

Linux arm64 runners are in public preview. Building the arm64 part of
the Docker image on one of these rather than in qemu should be a lot
faster; let's try it.

Author: anomiex

.github/workflows/build-docker.yml

@@ -21,20 +21,108 @@ concurrency:
 
 jobs:
   build:
-    name: Build and publish Jetpack Dev Environment
-    runs-on: ubuntu-latest
+    name: Build Jetpack Dev Environment (${{ matrix.platform }})
+    runs-on: ${{ matrix.runner }}
     permissions:
       packages: write
       contents: read
     timeout-minutes: 60  # 2021-10-26: Build for arm64 is S-L-O-W. Sigh.
+    strategy:
+      matrix:
+        include:
+          - runner: ubuntu-latest
+            platform: amd64
+          - runner: ubuntu-24.04-arm
+            platform: arm64
 
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up qemu
-        uses: docker/setup-qemu-action@v3
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Fetch build args
+        id: buildargs
+        run: |
+          source .github/versions.sh
+          source .github/files/gh-funcs.sh
+
+          gh_set_output php-version "$PHP_VERSION"
+          gh_set_output composer-version "$COMPOSER_VERSION"
+          gh_set_output node-version "$NODE_VERSION"
+          gh_set_output pnpm-version "$PNPM_VERSION"
+
+          # We're not git-tagging for the env. Just tag all trunk builds as latest.
+          if [[ "$GITHUB_EVENT_NAME" == "push" ]]; then
+            gh_set_output tags "type=raw,latest"
+            gh_set_output images $'automattic/jetpack-wordpress-dev\nghcr.io/automattic/jetpack-wordpress-dev'
+          elif [[ "$GITHUB_EVENT_NAME" == "pull_request" ]]; then
+            gh_set_output tags "type=ref,event=pr"
+            gh_set_output images "ghcr.io/automattic/jetpack-wordpress-dev"
+          else
+            echo "Unknown GITHUB_EVENT_NAME $GITHUB_EVENT_NAME"
+            exit 1
+          fi
+
+      - name: Extract Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          flavor: latest=false
+          tags: ${{ steps.buildargs.outputs.tags }}
+          images: ${{ steps.buildargs.outputs.images }}
+          labels: |
+            org.opencontainers.image.title=Jetpack Development Environment
+            org.opencontainers.image.description=Unified environment for developing in the Jetpack Monorepo using Docker containers.
+            org.opencontainers.image.documentation=${{ github.server_url }}/${{ github.repository }}/blob/trunk/tools/docker/README.md
+
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v6
         with:
-          platforms: arm64
+          context: tools/docker
+          platforms: linux/${{ matrix.platform }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          outputs: type=image,push-by-digest=true,name-canonical=true,push=true
+          build-args: |
+            PHP_VERSION=${{ steps.buildargs.outputs.php-version }}
+            COMPOSER_VERSION=${{ steps.buildargs.outputs.composer-version }}
+            NODE_VERSION=${{ steps.buildargs.outputs.node-version }}
+            PNPM_VERSION=${{ steps.buildargs.outputs.pnpm-version }}
+
+      - name: Export digest
+        env:
+          TEMP: ${{ runner.temp }}
+          DIGEST: ${{ steps.build.outputs.digest }}
+        run: |
+          mkdir -p "$TEMP/digests"
+          touch "$TEMP/digests/${DIGEST#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-linux-${{ matrix.platform }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    name: Merge and publish Jetpack Dev Environment
+    runs-on: ubuntu-latest
+    needs: build
+    permissions:
+      packages: write
+      contents: read
+    timeout-minutes: 60  # 2021-10-26: Build for arm64 is S-L-O-W. Sigh.
+
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: ${{ runner.temp }}/digests
+          pattern: digests-*
+          merge-multiple: true
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -87,16 +175,14 @@ jobs:
             org.opencontainers.image.description=Unified environment for developing in the Jetpack Monorepo using Docker containers.
             org.opencontainers.image.documentation=${{ github.server_url }}/${{ github.repository }}/blob/trunk/tools/docker/README.md
 
-      - name: Build and push Docker image
-        uses: docker/build-push-action@v6
-        with:
-          context: tools/docker
-          platforms: linux/amd64,linux/arm64
-          push: true
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-          build-args: |
-            PHP_VERSION=${{ steps.buildargs.outputs.php-version }}
-            COMPOSER_VERSION=${{ steps.buildargs.outputs.composer-version }}
-            NODE_VERSION=${{ steps.buildargs.outputs.node-version }}
-            PNPM_VERSION=${{ steps.buildargs.outputs.pnpm-version }}
+      - name: Create manifest list and push
+        working-directory: ${{ runner.temp }}/digests
+        run: |
+          docker buildx imagetools create $(jq -cr '.tags | map("-t " + .) | join(" ")' <<< "$DOCKER_METADATA_OUTPUT_JSON") \
+            $(printf "$REGISTRY_IMAGE@sha256:%s " *)
+
+      - name: Inspect image
+        env:
+          VERSION: ${{ steps.meta.outputs.version }}
+        run: |
+          docker buildx imagetools inspect "$REGISTRY_IMAGE:$VERSION"