feat: use multi-runner on docker publish (#6556)

## Summary

This PR parallelizes multi-platform builds using multiple workers (hence
the new docker-build / docker-publish jobs), this seems to save about ~8
minutes.

This is partial work extracted from
#6053 than is standalone

.github/workflows/build-docker.yml

@@ -17,12 +17,21 @@ on:
     paths:
       - .github/workflows/build-docker.yml
 
+env:
+  UV_BASE_IMG: ghcr.io/${{ github.repository_owner }}/uv
+
 jobs:
-  docker-publish:
-    name: Build Docker image (ghcr.io/astral-sh/uv)
+  docker-build:
+    name: Build Docker image (ghcr.io/astral-sh/uv) for ${{ matrix.platform }}
     runs-on: ubuntu-latest
     environment:
       name: release
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - linux/amd64
+          - linux/arm64
     steps:
       - uses: actions/checkout@v4
         with:
@@ -40,7 +49,7 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ghcr.io/astral-sh/uv
+          images: ${{ env.UV_BASE_IMG }}
 
       - name: Check tag consistency
         if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
@@ -55,14 +64,72 @@ jobs:
             echo "Releasing ${version}"
           fi
 
-      - name: "Build and push Docker image"
+      - name: Normalize Platform Pair (replace / with -)
+        run: |
+          platform=${{ matrix.platform }}
+          echo "PLATFORM_TUPLE=${platform//\//-}" >> $GITHUB_ENV
+
+      # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
+      - name: Build and push by digest
+        id: build
         uses: docker/build-push-action@v6
         with:
           context: .
-          platforms: linux/amd64,linux/arm64
-          # Reuse the builder
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
-          push: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
-          tags: ghcr.io/astral-sh/uv:latest,ghcr.io/astral-sh/uv:${{ (inputs.plan != '' && fromJson(inputs.plan).announcement_tag) || 'dry-run' }}
+          platforms: ${{ matrix.platform }}
+          cache-from: type=gha,scope=uv-${{ env.PLATFORM_TUPLE }}
+          cache-to: type=gha,mode=min,scope=uv-${{ env.PLATFORM_TUPLE }}
           labels: ${{ steps.meta.outputs.labels }}
+          outputs: type=image,name=${{ env.UV_BASE_IMG }},push-by-digest=true,name-canonical=true,push=${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
+
+      - name: Export digests
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload digests
+        uses: actions/upload-artifact@v4
+        with:
+          name: digests-${{ env.PLATFORM_TUPLE }}
+          path: /tmp/digests/*
+          if-no-files-found: error
+          retention-days: 1
+
+  docker-publish:
+    name: Publish Docker image (ghcr.io/astral-sh/uv)
+    runs-on: ubuntu-latest
+    environment:
+      name: release
+    needs:
+      - docker-build
+    if: ${{ inputs.plan != '' && !fromJson(inputs.plan).announcement_tag_is_implicit }}
+    steps:
+      - name: Download digests
+        uses: actions/download-artifact@v4
+        with:
+          path: /tmp/digests
+          pattern: digests-*
+          merge-multiple: true
+
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.UV_BASE_IMG }}
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      # Adapted from https://docs.docker.com/build/ci/github-actions/multi-platform/
+      - name: Create manifest list and push
+        working-directory: /tmp/digests
+        run: |
+          docker buildx imagetools create \
+            -t ${{ env.UV_BASE_IMG }}:latest \
+            -t ${{ env.UV_BASE_IMG }}:${{ (inputs.plan != '' && fromJson(inputs.plan).announcement_tag) || 'dry-run' }} \
+            $(printf '${{ env.UV_BASE_IMG }}@sha256:%s ' *)

Dockerfile

@@ -1,4 +1,4 @@
-FROM --platform=$BUILDPLATFORM ubuntu as build
+FROM --platform=$BUILDPLATFORM ubuntu AS build
 ENV HOME="/root"
 WORKDIR $HOME