use native ARM runner for multi-arch Docker build

.github/workflows/docker.yml

@@ -12,8 +12,22 @@ env:
   IMAGE_NAME: ${{ github.repository }}
 
 jobs:
+  # ===========================================================
+  # Build platform-specific images on native runners
+  # ===========================================================
   build:
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: linux/amd64
+            runner: ubuntu-latest
+            suffix: amd64
+          - platform: linux/arm64
+            runner: ubuntu-24.04-arm
+            suffix: arm64
+
+    runs-on: ${{ matrix.runner }}
     permissions:
       contents: read
       packages: write
@@ -22,9 +36,6 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
-      - name: Set up QEMU (for multi-arch builds)
-        uses: docker/setup-qemu-action@v3
-
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
@@ -36,6 +47,68 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: Extract metadata (tags, labels)
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+
+      - name: Build and push by digest
+        id: build
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          platforms: ${{ matrix.platform }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha,scope=${{ matrix.suffix }}
+          cache-to: type=gha,scope=${{ matrix.suffix }},mode=max
+          outputs: ${{ github.event_name != 'pull_request' && format('type=image,name={0}/{1},push-by-digest=true,name-canonical=true,push=true', env.REGISTRY, env.IMAGE_NAME) || 'type=docker' }}
+
+      - name: Export digest
+        if: github.event_name != 'pull_request'
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        if: github.event_name != 'pull_request'
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ matrix.suffix }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  # ===========================================================
+  # Merge platform digests into a single multi-arch manifest
+  # ===========================================================
+  merge:
+    runs-on: ubuntu-latest
+    if: github.event_name != 'pull_request'
+    needs: [build]
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Extract metadata (tags, labels)
         id: meta
         uses: docker/metadata-action@v5
@@ -50,13 +123,13 @@ jobs:
             type=semver,pattern={{version}}
             type=semver,pattern={{major}}.{{minor}}
 
-      - name: Build and push Docker image
-        uses: docker/build-push-action@v5
-        with:
-          context: .
-          platforms: linux/amd64,linux/arm64
-          push: ${{ github.event_name != 'pull_request' }}
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+      - 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.REGISTRY }}/${{ env.IMAGE_NAME }}@sha256:%s ' *)
+
+      - name: Inspect image
+        run: |
+          docker buildx imagetools inspect ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ steps.meta.outputs.version }}