GitHub Actions

Overview

GitHub Actions is a CI/CD platform integrated into GitHub. It automates build, test, and deployment workflows triggered by repository events.

Core Concepts

Workflow Structure

name: CI Pipeline
on:
  push:
    branches: [main, dev]
  pull_request:
    branches: [main]

env:
  NODE_VERSION: '20'

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [18, 20, 22]
    steps:
      - uses: actions/checkout@v4
      
      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node-version }}
          cache: 'npm'
      
      - run: npm ci
      - run: npm test
      - run: npm run lint
  
  build:
    needs: test
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: npm ci
      - run: npm run build
      - uses: actions/upload-artifact@v4
        with:
          name: build
          path: dist/
  
  deploy:
    needs: build
    if: github.ref == 'refs/heads/main'
    runs-on: ubuntu-latest
    environment: production
    steps:
      - uses: actions/download-artifact@v4
        with:
          name: build
      - run: ./deploy.sh

Common Patterns

Caching

- uses: actions/cache@v4
  with:
    path: ~/.npm
    key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}
    restore-keys: |
      ${{ runner.os }}-node-

Matrix Builds

strategy:
  matrix:
    os: [ubuntu-latest, windows-latest, macos-latest]
    python: ['3.9', '3.10', '3.11', '3.12']
  fail-fast: false  # Don't cancel other jobs on failure

Secrets

steps:
  - name: Deploy
    env:
      API_KEY: ${{ secrets.API_KEY }}
    run: ./deploy.sh

Reusable Workflows

# .github/workflows/reusable-test.yml
name: Reusable Test
on:
  workflow_call:
    inputs:
      node-version:
        type: string
        default: '20'
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ inputs.node-version }}
      - run: npm ci && npm test

# Caller workflow
jobs:
  test:
    uses: ./.github/workflows/reusable-test.yml
    with:
      node-version: '20'

Best Practices

1. Pin action versions — Use SHA or specific tags (@v4)
2. Cache dependencies — Speed up builds significantly
3. Use matrix testing — Test across multiple versions
4. Limit permissions — Set permissions: read-all by default
5. Use environments — Protect production deployments
6. Fail fast — fail-fast: true for matrix (default)
7. Timeout jobs — Prevent runaway processes

Interview Questions

1. GitHub Actions vs Jenkins? — GitHub Actions: cloud-native, YAML config, GitHub integration. Jenkins: self-hosted, Groovy plugins, more flexible.
2. How to share artifacts between jobs? — actions/upload-artifact and actions/download-artifact
3. How to handle secrets? — Repository/org/environment secrets, never hardcode
4. Self-hosted runners? — For custom hardware, private networks, GPU access. Security risk if public repo.
5. How to speed up workflows? — Caching, matrix parallelism, smaller Docker images, self-hosted runners
6. What is a composite action? — Reusable action combining multiple steps in one action.yml
7. How to deploy to multiple environments? — Use environment keyword, deployment protection rules
8. Scheduled workflows? — on: schedule: cron: '0 0 * * *'. Runs on default branch.
9. How to debug workflows? — Enable step debug logging (ACTIONS_STEP_DEBUG), tmate action
10. Concurrency control? — concurrency: group: deploy-${{ github.ref }} to prevent parallel deploys

Related Topics

• GitOps — Git-based deployment
• Docker — Containerized CI
• Kubernetes — Deployment target