Docker and Container WorkflowsLesson 3.1

How to build a Docker image in GitHub Actions

docker build command, Dockerfile basics, context path, image tagging, build args, multi-stage builds in CI, build output

Building Images in CI

Building a Docker image in CI ensures your image is always built from clean code, not a developer's local environment. The image becomes a verified, deployable artifact.

Basic Docker Build Workflow

jobs:
  build-image:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Build Docker image
        run: |
          docker build \
            --tag myapp:${{ github.sha }} \
            --tag myapp:latest \
            --file Dockerfile \
            .

github.sha is a built-in context variable containing the full commit SHA. Tagging with it makes every image uniquely traceable to a commit — critical for rollbacks.

Using docker/build-push-action

- uses: docker/build-push-action@v5
  with:
    context: .
    file: ./Dockerfile
    push: false
    tags: myapp:${{ github.sha }}

The official docker/build-push-action is the recommended approach for production workflows. It supports BuildKit by default, enabling parallel layer builds and better caching. Set push: false to build without pushing — useful in PR checks where you only want to verify the image builds successfully.