ci(release): build docker images natively per arch and merge manifests (#1507)

Multi-arch images were built on a single amd64 runner with QEMU
emulating arm64. The Next.js build (Dockerfile.web) under emulation
took 30+ minutes per release and was the long pole of the workflow.

Split each image build across two native runners (amd64 on
ubuntu-latest, arm64 on ubuntu-24.04-arm), push by digest, then
merge into a manifest list with docker buildx imagetools. QEMU is
no longer needed.

Backend and web each become a (matrix build + merge) pair, replacing
the previous single docker-images job. Per-platform GHA cache scopes
avoid cross-arch cache eviction.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/release.yml

@@ -78,18 +78,38 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           HOMEBREW_TAP_GITHUB_TOKEN: ${{ secrets.HOMEBREW_TAP_GITHUB_TOKEN }}
 
-  docker-images:
+  # Multi-arch images are built natively per platform on dedicated runners
+  # (amd64 on ubuntu-latest, arm64 on ubuntu-24.04-arm) and merged into a
+  # manifest list. This avoids QEMU emulation, which was making the Next.js
+  # arm64 build run for 30+ minutes per release.
+  docker-backend-build:
     needs: verify
-    runs-on: ubuntu-latest
-    concurrency:
-      group: release-docker-images-${{ github.ref }}
-      cancel-in-progress: true
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: linux/amd64
+            runs-on: ubuntu-latest
+          - platform: linux/arm64
+            runs-on: ubuntu-24.04-arm
+    runs-on: ${{ matrix.runs-on }}
     steps:
+      - name: Prepare
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> "$GITHUB_ENV"
+
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Setup QEMU
-        uses: docker/setup-qemu-action@v3
+      - name: Compute backend image labels
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/multica-backend
+          labels: |
+            org.opencontainers.image.title=Multica Backend
+            org.opencontainers.image.description=Multica self-hosted backend
 
       - name: Setup Docker Buildx
         uses: docker/setup-buildx-action@v3
@@ -101,8 +121,55 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          file: Dockerfile
+          pull: true
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=release-backend-${{ env.PLATFORM_PAIR }}
+          cache-to: type=gha,mode=max,scope=release-backend-${{ env.PLATFORM_PAIR }}
+          build-args: |
+            VERSION=${{ needs.verify.outputs.tag_name }}
+            COMMIT=${{ github.sha }}
+          outputs: type=image,name=ghcr.io/${{ github.repository_owner }}/multica-backend,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-backend-${{ env.PLATFORM_PAIR }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  docker-backend-merge:
+    needs: [verify, docker-backend-build]
+    runs-on: ubuntu-latest
+    concurrency:
+      group: release-docker-backend-${{ github.ref }}
+      cancel-in-progress: true
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-backend-*
+          merge-multiple: true
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: Compute backend image tags
-        id: meta_backend
+        id: meta
         uses: docker/metadata-action@v5
         with:
           images: ghcr.io/${{ github.repository_owner }}/multica-backend
@@ -112,28 +179,114 @@ jobs:
             type=raw,value=latest,enable=${{ needs.verify.outputs.is_stable == 'true' }}
             type=raw,value=${{ needs.verify.outputs.tag_name }}
             type=sha,prefix=sha-
-          labels: |
-            org.opencontainers.image.title=Multica Backend
-            org.opencontainers.image.description=Multica self-hosted backend
 
-      - name: Build and push backend image
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        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") \
+            $(printf 'ghcr.io/${{ github.repository_owner }}/multica-backend@sha256:%s ' *)
+
+      - name: Inspect image
+        run: |
+          docker buildx imagetools inspect \
+            ghcr.io/${{ github.repository_owner }}/multica-backend:${{ steps.meta.outputs.version }}
+
+  docker-web-build:
+    needs: verify
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: linux/amd64
+            runs-on: ubuntu-latest
+          - platform: linux/arm64
+            runs-on: ubuntu-24.04-arm
+    runs-on: ${{ matrix.runs-on }}
+    steps:
+      - name: Prepare
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> "$GITHUB_ENV"
+
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Compute web image labels
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/multica-web
+          labels: |
+            org.opencontainers.image.title=Multica Web
+            org.opencontainers.image.description=Multica self-hosted web frontend
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push by digest
+        id: build
         uses: docker/build-push-action@v6
         with:
           context: .
-          file: Dockerfile
+          file: Dockerfile.web
           pull: true
-          push: true
-          platforms: linux/amd64,linux/arm64
-          labels: ${{ steps.meta_backend.outputs.labels }}
-          tags: ${{ steps.meta_backend.outputs.tags }}
-          cache-from: type=gha,scope=release-backend
-          cache-to: type=gha,mode=max,scope=release-backend
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=release-web-${{ env.PLATFORM_PAIR }}
+          cache-to: type=gha,mode=max,scope=release-web-${{ env.PLATFORM_PAIR }}
           build-args: |
-            VERSION=${{ needs.verify.outputs.tag_name }}
-            COMMIT=${{ github.sha }}
+            REMOTE_API_URL=http://backend:8080
+            NEXT_PUBLIC_APP_VERSION=${{ needs.verify.outputs.tag_name }}
+          outputs: type=image,name=ghcr.io/${{ github.repository_owner }}/multica-web,push-by-digest=true,name-canonical=true,push=true
+
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-web-${{ env.PLATFORM_PAIR }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  docker-web-merge:
+    needs: [verify, docker-web-build]
+    runs-on: ubuntu-latest
+    concurrency:
+      group: release-docker-web-${{ github.ref }}
+      cancel-in-progress: true
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-web-*
+          merge-multiple: true
+
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v3
 
       - name: Compute web image tags
-        id: meta_web
+        id: meta
         uses: docker/metadata-action@v5
         with:
           images: ghcr.io/${{ github.repository_owner }}/multica-web
@@ -143,25 +296,25 @@ jobs:
             type=raw,value=latest,enable=${{ needs.verify.outputs.is_stable == 'true' }}
             type=raw,value=${{ needs.verify.outputs.tag_name }}
             type=sha,prefix=sha-
-          labels: |
-            org.opencontainers.image.title=Multica Web
-            org.opencontainers.image.description=Multica self-hosted web frontend
 
-      - name: Build and push web image
-        uses: docker/build-push-action@v6
+      - name: Login to GHCR
+        uses: docker/login-action@v3
         with:
-          context: .
-          file: Dockerfile.web
-          pull: true
-          push: true
-          platforms: linux/amd64,linux/arm64
-          labels: ${{ steps.meta_web.outputs.labels }}
-          tags: ${{ steps.meta_web.outputs.tags }}
-          cache-from: type=gha,scope=release-web
-          cache-to: type=gha,mode=max,scope=release-web
-          build-args: |
-            REMOTE_API_URL=http://backend:8080
-            NEXT_PUBLIC_APP_VERSION=${{ needs.verify.outputs.tag_name }}
+          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") \
+            $(printf 'ghcr.io/${{ github.repository_owner }}/multica-web@sha256:%s ' *)
+
+      - name: Inspect image
+        run: |
+          docker buildx imagetools inspect \
+            ghcr.io/${{ github.repository_owner }}/multica-web:${{ steps.meta.outputs.version }}
 
   # Build the Desktop installers for Linux and Windows and upload them to
   # the GitHub Release that the `release` job above just published. macOS