Recap — CI/CD Workflows and Common Patterns

# CI/CD Workflows and Common Patterns GitHub Actions runs your code on GitHub's infrastructure when events happen (push, PR, schedule). The CI/CD layer for most modern projects. ## Workflow basics A workflow is a YAML file in `.github/workflows/`: ```yaml # .github/workflows/test.yml name: Test on: push: branches: [main] pull_request: branches: [main] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-python@v5 with: python-version: '3.12' - run: pip install -e ".[dev]" - run: pytest ``` Three key parts: - **on**: which events trigger the workflow. - **jobs**: parallel groups of steps. - **steps**: actions or shell commands to run. ## Events (triggers) ```yaml on: push: # any push branches: [main] # only to main paths: ['src/**'] # only when src/ changes pull_request: # PR opened, sync'd, etc. types: [opened, synchronize] schedule: - cron: '0 9 * * *' # daily at 9 UTC workflow_dispatch: # manual trigger from UI release: types: [published] ``` Combine: `on: [push, pull_request]` for both. ## Jobs and steps ```yaml jobs: lint: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - run: ruff check . test: runs-on: ubuntu-latest needs: lint # only run if lint passed steps: - uses: actions/checkout@v4 - run: pytest ``` `needs:` makes jobs sequential. Without it, parallel by default. Each job runs in a fresh VM (no state between jobs). ## Reusable actions ```yaml - uses: actions/checkout@v4 # popular: checkout code - uses: actions/setup-python@v5 with: python-version: '3.12' - uses: actions/setup-node@v4 with: node-version: '20' - uses: docker/setup-buildx-action@v3 ``` Marketplace: github.com/marketplace?type=actions. Thousands of pre-built actions. ## Matrix builds Run on multiple configs: ```yaml jobs: test: runs-on: ${{ matrix.os }} strategy: matrix: os: [ubuntu-latest, macos-latest, windows-latest] python: ['3.11', '3.12', '3.13'] steps: - uses: actions/checkout@v4 - uses: actions/setup-python@v5 with: python-version: ${{ matrix.python }} - run: pytest ``` Runs 3 × 3 = 9 jobs in parallel. ## Caching Speed up by caching dependencies: ```yaml - uses: actions/setup-python@v5 with: python-version: '3.12' cache: 'pip' # auto-cache pip - name: Cache node_modules uses: actions/cache@v4 with: path: node_modules key: ${{ runner.os }}-node-${{ hashFiles('package-lock.json') }} ``` ## Secrets Don't hardcode tokens: ```yaml - name: Deploy run: deploy_script env: DEPLOY_TOKEN: ${{ secrets.DEPLOY_TOKEN }} ``` Set secrets in: GitHub repo → Settings → Secrets and variables → Actions. GitHub provides `GITHUB_TOKEN` automatically (limited scope; for GitHub API operations). ## Conditional steps ```yaml - name: Deploy if: github.ref == 'refs/heads/main' run: deploy.sh - name: Notify Slack if: failure() # only on failure run: notify.sh ``` ## Common patterns ### Pattern 1: Test on PR ```yaml name: Test on: pull_request: branches: [main] jobs: test: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-python@v5 with: python-version: '3.12' - run: pip install -e ".[dev]" - run: ruff check . - run: pyright - run: pytest --cov=src ``` Required check: blocks merge if any step fails. ### Pattern 2: Build and test, then deploy on main ```yaml name: Deploy on: push: branches: [main] jobs: build: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - run: docker build -t myapp . deploy: needs: build runs-on: ubuntu-latest steps: - run: ./deploy.sh env: AWS_KEY: ${{ secrets.AWS_KEY }} ``` ### Pattern 3: Publish to PyPI on tag ```yaml name: Publish on: push: tags: ['v*'] jobs: publish: runs-on: ubuntu-latest steps: - uses: actions/checkout@v4 - uses: actions/setup-python@v5 - run: pip install build - run: python -m build - uses: pypa/gh-action-pypi-publish@release/v1 with: password: ${{ secrets.PYPI_TOKEN }} ``` ### Pattern 4: Scheduled task ```yaml name: Backup on: schedule: - cron: '0 2 * * *' # 2am daily jobs: backup: runs-on: ubuntu-latest steps: - run: ./backup.sh env: DB_URL: ${{ secrets.DB_URL }} ``` ## Status badges Add to README: ```markdown ![Tests](https://github.com/you/repo/actions/workflows/test.yml/badge.svg) ``` Shows pass/fail status. ## Limits and pricing Free tier: - Public repos: unlimited. - Private repos: 2,000 minutes/month. For most small projects: free. For h