Build multi-arch images natively instead of with QEMU

Replace QEMU emulation with native runners for amd64 and arm64 builds.
Each platform builds in parallel, uploads its digest as an artifact, and
a final merge job combines them into a single multi-arch manifest.

Author: ezhlobo

.github/workflows/release-image.yml

@@ -9,8 +9,16 @@ on:
       - image/**
 
 jobs:
-  build-and-push:
-    runs-on: ubuntu-latest
+  build:
+    strategy:
+      matrix:
+        include:
+          - platform: linux/amd64
+            runner: ubuntu-latest
+          - platform: linux/arm64
+            runner: ubuntu-24.04-arm
+
+    runs-on: ${{ matrix.runner }}
     permissions:
       contents: read
       packages: write
@@ -26,20 +34,69 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_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
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository_owner }}/devcontainer
+
+      - name: Build and push by digest
+        id: build
         uses: docker/build-push-action@v6
         with:
           context: ./image
-          platforms: linux/amd64,linux/arm64
-          push: true
-          tags: |
-            ghcr.io/${{ github.repository_owner }}/devcontainer:latest
-            ghcr.io/${{ github.repository_owner }}/devcontainer:${{ github.sha }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          outputs: type=image,name=ghcr.io/${{ github.repository_owner }}/devcontainer,push-by-digest=true,name-canonical=true,push=true
+          cache-from: type=gha,scope=${{ matrix.platform }}
+          cache-to: type=gha,mode=max,scope=${{ matrix.platform }}
+
+      - 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-${{ matrix.runner }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge:
+    runs-on: ubuntu-latest
+    needs: build
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: ${{ runner.temp }}/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Create and push manifest
+        working-directory: ${{ runner.temp }}/digests
+        run: |
+          docker buildx imagetools create \
+            -t ghcr.io/${{ github.repository_owner }}/devcontainer:latest \
+            -t ghcr.io/${{ github.repository_owner }}/devcontainer:${{ github.sha }} \
+            $(printf 'ghcr.io/${{ github.repository_owner }}/devcontainer@sha256:%s ' *)