This GitHub Actions workflow builds a Docker image and pushes it a container registry every time someone commits to main.

build_and_push_docker_hub.yaml

name: Build and push to Docker Hub
on:
  push:
    branches:
      - main

jobs:
  push_to_docker_hub:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Log in to Docker Hub
        run: |
          echo ${{ secrets.DOCKERHUB_PASSWORD }} | docker login -u ${{ secrets.DOCKERHUB_USERNAME }} --password-stdin

      - name: Build and tag image
        run: |
          COMMIT_SHA=$(echo $GITHUB_SHA | cut -c1-7)
          docker build -t ${{ secrets.DOCKERHUB_USERNAME }}/${{ github.repository }}:$COMMIT_SHA -f path/to/Dockerfile .

      - name: Push image to Docker Hub
        run: docker push ${{ secrets.DOCKERHUB_USERNAME }}/${{ github.repository }}:$COMMIT_SHA

build_and_push_ghcr.yaml

name: Build and push to GHCR
on:
  push:
    branches:
      - main

jobs:
  push_to_ghcr:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Log in to ghcr.io
        run: echo "${{ secrets.GHCR_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin

      - name: Build and tag image
        run: |
          COMMIT_SHA=$(echo $GITHUB_SHA | cut -c1-7)
          docker build -t ghcr.io/${{ github.repository_owner }}/${{ github.repository }}:$COMMIT_SHA -f path/to/Dockerfile .

      - name: Push image to GHCR
        run: docker push ghcr.io/${{ github.repository_owner }}/${{ github.repository }}:$COMMIT_SHA

build_and_push_harbor.yaml

name: Build and push to Harbor
on:
  push:
    branches:
      - main

jobs:
  push_to_harbor:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Log in to Harbor
          run: |
            echo ${{ secrets.HARBOR_CREDENTIALS }} | base64 --decode | docker login -u $(cut -d ':' -f1 <<< "${{ secrets.HARBOR_CREDENTIALS }}") --password-stdin ${{ secrets.HARBOR_REGISTRY_URL }}

        - name: Build and tag image
          run: |
            COMMIT_SHA=$(echo $GITHUB_SHA | cut -c1-7)
            docker build -t ${{ secrets.HARBOR_REGISTRY_URL }}/project-name/${{ github.repository }}:$COMMIT_SHA -f path/to/Dockerfile .

        - name: Push image to Harbor
          run: docker push ${{ secrets.HARBOR_REGISTRY_URL }}/project-name/${{ github.repository }}:$COMMIT_SHA

Superb! thanks a lot!