docker-build-workflow/.github/workflows/reusable-docker-build.yaml

---
name: Docker Build and Push

on:

  # REUSABLE WORKFLOW with INPUTS
  # to keep this workflow simple, assumptions are made:
    # - only able to push to Docker Hub and/or GHCR (GHCR by default)
    # - Builds on PR with tag of `prNUMBER` (same tag each PR push)
    # - Builds on push to main branch with tag of `latest`
    # - Builds on tag push with semver

  workflow_call:
    # allow reuse of this workflow in other repos
    inputs:
      dockerhub-enable:
        description: Log into Docker Hub
        required: false
        default: false
        type: boolean
      ghcr-enable:
        description: Log into GHCR
        required: false
        default: true
        type: boolean
      comment-enable:
        description: Create a PR comment with image tags and labels
        required: false
        default: true
        type: boolean
      context:
        description: Docker context (path) to start build from
        required: false
        type: string
        default: .
      file:
        description: Dockerfile to build, relative to context path
        required: false
        type: string
      target:
        description: Build stage to target
        required: false
        type: string
      platforms:
        description: Platforms to build for
        required: false
        type: string
        # common ones: linux/amd64,linux/arm64,linux/arm/v7
        default: linux/amd64
      image-names:
        description: A list of the account/repo names for docker build
        required: false
        type: string
        default: |
          ${{ github.repository }}
          ghcr.io/${{ github.repository }}
      tag-rules:
        # https://github.com/marketplace/actions/docker-metadata-action#tags-input
        description: Use docker-metadata action to create tags from a key-value pair list in CSV format
        required: false
        type: string
        default: |
          type=raw,value=latest,enable=${{ endsWith(github.ref, github.event.repository.default_branch) }}
          type=raw,value=stable-{{date 'YYYYMMDDHHmmss'}},enable=${{ endsWith(github.ref, github.event.repository.default_branch) }}
          type=ref,event=pr
          type=raw,value=gha-${{ github.run_id }}
      flavor-rules:
        # https://github.com/marketplace/actions/docker-metadata-action#flavor-input
        description: Three rules to (optionally) set for tag-rules, latest, prefix, and suffix
        required: false
        type: string
        default: |
            latest=false

    secrets:
      dockerhub-username:
        description: Docker Hub username
        required: false
      dockerhub-token:
        description: Docker Hub token
        required: false

    outputs:
      ghcr-tag:
        description: "single-use tag for ghcr.io"
        value: ${{ jobs.build-image.outputs.ghcr-tag }}


# permissions: GITHUB_TOKEN are better set by the **calling** workflow
# but we'll set defaults here for reference
# https://docs.github.com/en/actions/using-workflows/reusing-workflows#supported-keywords-for-jobs-that-call-a-reusable-workflow

permissions:
  contents: read
  packages: write # needed to push docker image to ghcr.io
  pull-requests: write # needed to create and update comments in PRs

jobs:
  build-image:

    name: Build+Push

    runs-on: ubuntu-latest

    outputs:
      # only outputs the unique gha- image tag that's unique to each build
      ghcr-tag: ${{ steps.ghcr-tag.outputs.tag }}

    steps:
      -
        name: Checkout
        uses: actions/checkout@v3
      -
        # we need qemu and buildx so we can build multiple platforms later
        name: Set up QEMU
        id: qemu
        uses: docker/setup-qemu-action@v1
      -
        # BuildKit (used with `docker buildx`) is the best way to build images
        name: Set up Docker Buildx
        id: buildx
        uses: docker/setup-buildx-action@v1
      -
        name: Login to DockerHub
        if: inputs.dockerhub-enable
        uses: docker/login-action@v1
        with:
          username: ${{ secrets.dockerhub-username }}
          password: ${{ secrets.dockerhub-token }}
      -
        name: Login to GHCR
        if: inputs.ghcr-enable
        uses: docker/login-action@v1
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}
      -
        name: Docker meta
        id: docker_meta
        uses: docker/metadata-action@v3
        with:
          # list of Docker images to use as base name for tags
          images: ${{ inputs.image-names }}
          flavor: ${{ inputs.flavor-rules }}
          tags: ${{ inputs.tag-rules }}
      -
        # this will build the images, once per platform,
        # then push to one or more registries (based on image list above in docker_meta)
        name: Docker Build and Push
        id: build_image
        uses: docker/build-push-action@v2
        with:
          platforms: ${{ inputs.platforms }}
          context: ${{ inputs.context }}
          file: ${{ inputs.file }}
          target: ${{ inputs.target }}
          builder: ${{ steps.buildx.outputs.name }}
          # it uses github cache API for faster builds:
          # https://github.com/docker/build-push-action/blob/master/docs/advanced/cache.md#cache-backend-api
          cache-from: type=gha
          cache-to: type=gha,mode=max
          push: true
          tags: ${{ steps.docker_meta.outputs.tags }}
          labels: ${{ steps.docker_meta.outputs.labels }}
      -
        # If PR, put image tags in the PR comments
        # from https://github.com/marketplace/actions/create-or-update-comment
        name: Find comment for image tags
        uses: peter-evans/find-comment@v1
        if: github.event_name == 'pull_request' && inputs.comment-enable
        id: fc
        with:
          issue-number: ${{ github.event.pull_request.number }}
          comment-author: 'github-actions[bot]'
          body-includes: Docker image tag(s) pushed
      
        # If PR, put image tags in the PR comments
      - name: Create or update comment for image tags
        uses: peter-evans/create-or-update-comment@v2
        if: github.event_name == 'pull_request' && inputs.comment-enable
        with:
          comment-id: ${{ steps.fc.outputs.comment-id }}
          issue-number: ${{ github.event.pull_request.number }}
          body: |
            Docker image tag(s) pushed:
            ```text
            ${{ steps.docker_meta.outputs.tags }}
            ```

            Labels added to images:
            ```text
            ${{ steps.docker_meta.outputs.labels }}
            ```
          edit-mode: replace

      - name: Find the gha-run-based image tag we just pushed to ghcr.io
        id: ghcr-tag
        run: |
          echo '::echo::on'
          echo "::set-output name=tag::gha-${{ github.run_id }}"