Split Docker builds across native amd64 and arm64 runners

.github/workflows/docker.yml

@@ -16,17 +16,30 @@ on:
 
 env:
   DOCKER_IMAGE: insprill/intellectual
-  DOCKER_PLATFORMS: linux/amd64,linux/arm64
+  DOCKER_TAG: ${{ startsWith(github.ref, 'refs/tags/v') && 'latest' || 'develop' }}
 
 jobs:
   build-docker:
-    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - platform: linux/amd64
+            runner: ubuntu-latest
+          - platform: linux/arm64
+            runner: ubuntu-24.04-arm
+    runs-on: ${{ matrix.runner }}
+    outputs:
+      push: ${{ env.DOCKER_PUSH }}
     steps:
       - name: Checkout Repository
         uses: actions/checkout@v7
 
       - name: Set Docker push status
-        run: echo "DOCKER_PUSH=${{ !env.ACT && (github.ref == 'refs/heads/master' || startsWith(github.ref, 'refs/tags/v')) && github.event_name != 'pull_request' }}" >> $GITHUB_ENV
+        run: |
+          echo "DOCKER_PUSH=${{ !env.ACT && (github.ref == 'refs/heads/master' || startsWith(github.ref, 'refs/tags/v')) && github.event_name != 'pull_request' }}" >> $GITHUB_ENV
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
 
       - name: Setup act
         run: "sudo chown runner:docker /var/run/docker.sock"
@@ -54,12 +67,57 @@ jobs:
           echo "IN_GIT_TAGGED=$([[ -n $(git describe --tags --exact-match) ]] && echo true || echo false)" >> .env
           echo "IN_GIT_REMOTE_URL=$(git remote get-url origin)" >> .env
 
-      - name: Build & Push
+      - name: Build & Push by digest
+        id: build
         uses: docker/build-push-action@v7
         with:
           context: . # Required for running with act
-          push: ${{ env.DOCKER_PUSH == 'true' }}
-          tags: ${{ env.DOCKER_IMAGE }}:${{ startsWith(github.ref, 'refs/tags/v') && 'latest' || 'develop' }}
-          platforms: ${{ env.DOCKER_PLATFORMS }}
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
+          tags: ${{ env.DOCKER_IMAGE }}
+          platforms: ${{ matrix.platform }}
+          outputs: type=image,push-by-digest=true,name-canonical=true,push=${{ env.DOCKER_PUSH }}
+          # Each platform needs its own scope, or the two builds overwrite each other's cache
+          cache-from: type=gha,scope=${{ env.PLATFORM_PAIR }}
+          cache-to: type=gha,mode=max,scope=${{ env.PLATFORM_PAIR }}
+
+      - name: Export digest
+        if: ${{ env.DOCKER_PUSH == 'true' }}
+        run: |
+          mkdir -p ${{ runner.temp }}/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "${{ runner.temp }}/digests/${digest#sha256:}"
+
+      - name: Upload digest
+        if: ${{ env.DOCKER_PUSH == 'true' }}
+        uses: actions/upload-artifact@v7
+        with:
+          name: digests-${{ env.PLATFORM_PAIR }}
+          path: ${{ runner.temp }}/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  merge-docker:
+    runs-on: ubuntu-latest
+    needs: build-docker
+    if: ${{ needs.build-docker.outputs.push == 'true' }}
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v8
+        with:
+          path: ${{ runner.temp }}/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v4
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v4
+
+      - name: Create manifest list & Push
+        working-directory: ${{ runner.temp }}/digests
+        run: |
+          docker buildx imagetools create -t ${{ env.DOCKER_IMAGE }}:${{ env.DOCKER_TAG }} \
+            $(printf '${{ env.DOCKER_IMAGE }}@sha256:%s ' *)