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In this lesson, you’ll extend your GitHub Actions CI workflow to publish a Docker image to Docker Hub. We’ll build the image for testing, verify it runs correctly, and then push it to your Docker Hub registry—all within a single workflow file.
Ensure you’ve configured the following GitHub repository secrets:
  • DOCKERHUB_USERNAME
  • DOCKERHUB_TOKEN
  • MONGO_URI, MONGO_USERNAME, MONGO_PASSWORD

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Updated Workflow Snippet

Add these three steps to your .github/workflows/ci.yml: 
# 1. Build the Docker image without pushing
- name: Docker Build for Testing
  uses: docker/build-push-action@v4
  with:
    context: .
    push: false                   # disable push during test build
    tags: ${{ vars.DOCKERHUB_USERNAME }}/solar-system:${{ github.sha }}

# 2. Run tests against the local image
- name: Docker Image Testing
  run: |
    docker images
    docker run --name solar-system-app -d \
      -p 3000:3000 \
      -e MONGO_URI=${{ secrets.MONGO_URI }} \
      -e MONGO_USERNAME=${{ secrets.MONGO_USERNAME }} \
      -e MONGO_PASSWORD=${{ secrets.MONGO_PASSWORD }} \
      ${{ vars.DOCKERHUB_USERNAME }}/solar-system:${{ github.sha }}

    # Inspect container IP and test /live endpoint
    IP=$(docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' solar-system-app)
    echo "Container IP: $IP"
    echo "Testing /live endpoint"
    wget -qO- "http://127.0.0.1:3000/live" | grep live

# 3. Push the tested image to Docker Hub
- name: Docker Push
  uses: docker/build-push-action@v4
  with:
    context: .
    push: true                    # enable push to registry
    tags: ${{ vars.DOCKERHUB_USERNAME }}/solar-system:${{ github.sha }}
After you commit and push, GitHub Actions will execute the build, test, and push steps in sequence.

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Step-by-Step Breakdown

Step NameActionDescription
Docker Build for Testingdocker/build-push-action@v4Builds the image locally without pushing to the registry
Docker Image TestingrunStarts a container, retrieves its IP, and tests the /live endpoint
Docker Pushdocker/build-push-action@v4Re-builds (using cache) and uploads all layers to Docker Hub

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Inspecting the Push Logs

During the Docker Push step you’ll see output similar to: 
/usr/bin/docker buildx build \
  --iidfile /tmp/docker-actions-toolkit/iidfile \
  --tag youruser/solar-system:e8095fb98a5b01249548095eaf3a9c371c274430 \
  --push .
This confirms that Buildx is pushing each layer of your image to Docker Hub.

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Verify the Image on Docker Hub

Once the workflow completes:
  1. Go to your repository on Docker Hub.
  2. Look under Tags for the SHA-based tag (e.g., e8095fb98a5b01249548095eaf3a9c371c274430).
If you see authentication errors, double-check that DOCKERHUB_TOKEN is up to date and has the correct permissions.

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Manual Push (Optional)

You can also push an existing local image with: 
docker push youruser/solar-system:tagname

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