Build on runners matching the platform to compile for

Author: SimplyDanny

.github/workflows/docker.yml

@@ -55,18 +55,67 @@ jobs:
       env:
         REPOSITORY: ${{ github.repository }}
 
-  build:
-    name: Build Image
+  build-amd64:
+    name: Build AMD64 Image
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: read
+      packages: write
+    needs: set-context
+    steps:
+    - uses: actions/checkout@v4
+      if: needs.set-context.outputs.checkout-ref == 'pr'
+    - uses: actions/checkout@v4
+      if: needs.set-context.outputs.checkout-ref != 'pr'
+      with:
+        ref: ${{ needs.set-context.outputs.checkout-ref }}
+    - name: Set up Docker Buildx
+      uses: docker/setup-buildx-action@v3
+    - name: Login to GitHub registry
+      uses: docker/login-action@v3
+      with:
+        username: ${{ github.actor }}
+        password: ${{ secrets.GITHUB_TOKEN }}
+        registry: ghcr.io
+    - name: Build and push by digest
+      id: build
+      uses: docker/build-push-action@v6
+      with:
+        context: .
+        platforms: linux/amd64
+        outputs: >-
+          type=image,
+          name=ghcr.io/${{ needs.set-context.outputs.repository-lc }},
+          push-by-digest=true,
+          name-canonical=true,
+          push=true
+        cache-from: >-
+          type=gha,
+          scope=build-amd64
+        cache-to: >-
+          type=gha,
+          mode=max,
+          scope=build-amd64
+    - 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-amd64
+        path: /tmp/digests/*
+        if-no-files-found: error
+        retention-days: 1
+
+  build-arm64:
+    name: Build ARM64 Image
     runs-on: ubuntu-24.04-arm
     permissions:
       contents: read
       packages: write
     needs: set-context
-    strategy:
-      matrix:
-        platform:
-          - linux/amd64
-          - linux/arm64
     steps:
     - uses: actions/checkout@v4
       if: needs.set-context.outputs.checkout-ref == 'pr'
@@ -87,7 +136,7 @@ jobs:
       uses: docker/build-push-action@v6
       with:
         context: .
-        platforms: ${{ matrix.platform }}
+        platforms: linux/arm64
         outputs: >-
           type=image,
           name=ghcr.io/${{ needs.set-context.outputs.repository-lc }},
@@ -96,11 +145,11 @@ jobs:
           push=true
         cache-from: >-
           type=gha,
-          scope=build-${{ strategy.job-index }}
+          scope=build-arm64
         cache-to: >-
           type=gha,
           mode=max,
-          scope=build-${{ strategy.job-index }}
+          scope=build-arm64
     - name: Export digest
       run: |
         mkdir -p /tmp/digests
@@ -109,7 +158,7 @@ jobs:
     - name: Upload digest
       uses: actions/upload-artifact@v4
       with:
-        name: digests-${{ strategy.job-index }}
+        name: digests-arm64
         path: /tmp/digests/*
         if-no-files-found: error
         retention-days: 1
@@ -121,7 +170,8 @@ jobs:
       packages: write
     needs:
       - set-context
-      - build
+      - build-amd64
+      - build-arm64
     steps:
     - name: Download digests
       uses: actions/download-artifact@v4