docker.yml

name: docker

# Multi-arch image publish using split native runners (no QEMU).
#
# Flow:
#   1. `build` matrix runs in parallel:
#        - linux/amd64 on ubuntu-latest (native x86_64)
#        - linux/arm64 on ubuntu-24.04-arm (native arm64; free for public repos)
#      Each produces a digest-only image push (no tags yet).
#   2. `merge` job pulls both digests and assembles a multi-arch manifest list
#      under the final tags (semver + `latest`).
#
# Each arch takes ~10 min to compile natively. Total wall time ≈ 12 min,
# vs ~60 min when arm64 was emulated with QEMU on an amd64 runner.

on:
  push:
    tags: ["v*"]
  workflow_dispatch:

permissions:
  contents: read
  packages: write

env:
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}

jobs:
  build:
    strategy:
      fail-fast: false
      matrix:
        include:
          - platform: linux/amd64
            runner: ubuntu-latest
          - platform: linux/arm64
            runner: ubuntu-24.04-arm
    runs-on: ${{ matrix.runner }}
    timeout-minutes: 45
    steps:
      - uses: actions/checkout@v4
      - name: Prepare platform slug
        run: |
          platform="${{ matrix.platform }}"
          echo "PLATFORM_PAIR=${platform//\//-}" >> "$GITHUB_ENV"

      - uses: docker/metadata-action@v5
        id: meta
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}

      - uses: docker/setup-buildx-action@v3

      - uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - id: build
        uses: docker/build-push-action@v5
        with:
          context: .
          platforms: ${{ matrix.platform }}
          labels: ${{ steps.meta.outputs.labels }}
          # push-by-digest keeps this image nameless-but-pushed; the merge
          # job will stitch the per-arch digests into the final tags.
          outputs: type=image,name=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }},push-by-digest=true,name-canonical=true,push=true
          cache-from: type=gha,scope=${{ env.PLATFORM_PAIR }}
          cache-to: type=gha,mode=max,scope=${{ env.PLATFORM_PAIR }}

      - name: Export digest
        run: |
          mkdir -p /tmp/digests
          digest="${{ steps.build.outputs.digest }}"
          touch "/tmp/digests/${digest#sha256:}"

      - uses: actions/upload-artifact@v4
        with:
          name: digests-${{ env.PLATFORM_PAIR }}
          path: /tmp/digests/*
          if-no-files-found: error
          retention-days: 1

  merge:
    needs: build
    runs-on: ubuntu-latest
    steps:
      - uses: actions/download-artifact@v4
        with:
          path: /tmp/digests
          pattern: digests-*
          merge-multiple: true

      - uses: docker/setup-buildx-action@v3

      - uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          tags: |
            type=ref,event=tag
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
            type=raw,value=latest,enable={{is_default_branch}}

      - 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 }}