GitHub Actions & GitLab CI

🎯 Learning Objectives

• Master GitHub Actions workflows
• Learn GitLab CI/CD pipelines
• Understand CI/CD best practices
• Build and deploy applications

GitHub Actions and GitLab CI are modern CI/CD platforms. This chapter covers both with practical examples.

Interview Focus

Be ready to explain workflow syntax, triggers, jobs, and steps. Understand when to use which platform.

GitHub Actions

Basic Workflow

name: CI Pipeline

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Setup Node.js
        uses: actions/setup-node@v3
        with:
          node-version: '18'

      - name: Install dependencies
        run: npm install

      - name: Run tests
        run: npm test

      - name: Build
        run: npm run build

Workflow Components

• on: Triggers (push, PR, schedule, etc.)
• jobs: Parallel or sequential tasks
• steps: Individual commands or actions
• runs-on: Runner environment

Docker Build and Push

name: Build and Push Docker Image

on:
  push:
    branches: [main]
    tags:
      - 'v*'

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2

      - name: Login to Docker Hub
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_PASSWORD }}

      - name: Build and push
        uses: docker/build-push-action@v4
        with:
          context: .
          push: true
          tags: user/app:latest

Matrix Strategy

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        node-version: [14, 16, 18]
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-node@v3
        with:
          node-version: ${{ matrix.node-version }}
      - run: npm test

Matrix Benefits

Test against multiple versions simultaneously, saving time and ensuring compatibility.

Secrets and Environment Variables

env:
  NODE_ENV: production

jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Use secret
        run: echo ${{ secrets.API_KEY }}

      - name: Use environment variable
        run: echo $NODE_ENV

Security Best Practices

• Never commit secrets to repository
• Use GitHub Secrets for sensitive data
• Rotate secrets regularly
• Use least privilege principle

GitLab CI

Basic Pipeline

# .gitlab-ci.yml
stages:
  - build
  - test
  - deploy

build:
  stage: build
  image: node:18
  script:
    - npm install
    - npm run build
  artifacts:
    paths:
      - dist/
    expire_in: 1 week

test:
  stage: test
  image: node:18
  script:
    - npm test
  coverage: '/Coverage: \d+\.\d+%/'

deploy:
  stage: deploy
  image: alpine:latest
  script:
    - ./deploy.sh
  only:
    - main

GitLab CI Concepts

• stages: Pipeline stages (sequential)
• jobs: Tasks within stages
• artifacts: Files passed between jobs
• only/except: Job triggers

Docker in GitLab CI

build-docker:
  stage: build
  image: docker:latest
  services:
    - docker:dind
  before_script:
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
  script:
    - docker build -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA

Conditional Jobs

deploy-staging:
  stage: deploy
  script: ./deploy.sh staging
  only:
    - develop

deploy-production:
  stage: deploy
  script: ./deploy.sh production
  only:
    - main
  when: manual

Best Practices

1. Fast Feedback

# Run quick tests first
jobs:
  lint:
    runs-on: ubuntu-latest
    steps:
      - run: npm run lint

  unit-tests:
    runs-on: ubuntu-latest
    steps:
      - run: npm test

  integration-tests:
    runs-on: ubuntu-latest
    needs: [lint, unit-tests]
    steps:
      - run: npm run test:integration

2. Caching

# GitHub Actions
- name: Cache dependencies
  uses: actions/cache@v3
  with:
    path: ~/.npm
    key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

# GitLab CI
cache:
  key: ${CI_COMMIT_REF_SLUG}
  paths:
    - node_modules/

3. Parallel Execution

# Run independent jobs in parallel
jobs:
  test-unit:
    # ...
  test-integration:
    # ...
  lint:
    # ...

Common Interview Questions

Q: When to use GitHub Actions vs GitLab CI?

Answer: - GitHub Actions: If using GitHub, integrated experience - GitLab CI: If using GitLab, more features, self-hosted runners easier - Both are powerful, choose based on your Git hosting

Q: Explain workflow triggers

Answer: - Push: On code push - Pull Request: On PR creation/update - Schedule: Cron-based (GitHub Actions) - Manual: Manual trigger (GitLab CI) - Webhook: External triggers

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