CI/CD Pipelines

What is CI/CD?

Continuous Integration (CI) means every time someone pushes code, it is automatically tested. Linting, unit tests, integration tests - all run automatically. If anything fails, the team knows immediately.

Continuous Deployment (CD) means that once tests pass, the code is automatically deployed to production. No human clicking buttons. Push to main, tests pass, it is live.

Together, they eliminate manual work, catch bugs early, and let you ship faster with confidence.

GitHub Actions - The Modern Standard

GitHub Actions is built into GitHub. You define workflows in YAML files inside .github/workflows/. This example runs tests on every push and pull request, then deploys to your server when code lands on main.

name: CI/CD Pipeline

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

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
          cache: npm
      - run: npm ci
      - run: npm run lint
      - run: npm test

  build-and-deploy:
    needs: test
    runs-on: ubuntu-latest
    if: github.ref == 'refs/heads/main'
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: 20
      - run: npm ci
      - run: npm run build
      - name: Deploy to server
        run: |
          rsync -avz ./dist/ user@server:/var/www/app/

Docker in CI/CD

A very common pattern is building a Docker image in CI and pushing it to a registry. Then your deployment step just pulls the new image and restarts the container.

name: Docker Build and Push

on:
  push:
    branches: [main]

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

      - name: Login to Docker Hub
        uses: docker/login-action@v3
        with:
          username: ${{ secrets.DOCKER_USERNAME }}
          password: ${{ secrets.DOCKER_TOKEN }}

      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          push: true
          tags: myuser/myapp:latest,myuser/myapp:${{ github.sha }}

Notice we tag with both "latest" and the git commit SHA. This gives you a stable tag and a way to trace exactly which commit is running.

Jenkins - The Enterprise Option

Jenkins is self-hosted, highly customisable, and has been around for years. You will encounter it at larger companies. Configuration lives in a Jenkinsfile.

pipeline {
  agent any
  stages {
    stage('Install') {
      steps {
        sh 'npm ci'
      }
    }
    stage('Test') {
      steps {
        sh 'npm test'
      }
    }
    stage('Build') {
      steps {
        sh 'npm run build'
      }
    }
    stage('Deploy') {
      when {
        branch 'main'
      }
      steps {
        sh './deploy.sh'
      }
    }
  }
}