CI/CD Fundamentals

CI/CD automates the path from code commit to production. CI catches bugs early by running tests on every push. CD ensures the artifact is always deployable — or deployed automatically.

GitHub Actions — Complete Workflow

# .github/workflows/ci.yml
name: CI

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

env:
  NODE_VERSION: '20'
  REGISTRY: ghcr.io
  IMAGE_NAME: ${{ github.repository }}

jobs:
  lint-and-test:
    name: Lint & Test
    runs-on: ubuntu-latest

    services:
      postgres:
        image: postgres:16
        env:
          POSTGRES_PASSWORD: postgres
          POSTGRES_DB: testdb
        ports: ['5432:5432']
        options: >-
          --health-cmd pg_isready
          --health-interval 10s
          --health-timeout 5s
          --health-retries 5

    steps:
      - uses: actions/checkout@v4

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: ${{ env.NODE_VERSION }}
          cache: 'npm'              # cache node_modules

      - name: Install dependencies
        run: npm ci                 # clean install from lockfile

      - name: Lint
        run: npm run lint

      - name: Type check
        run: npm run typecheck

      - name: Run tests
        run: npm run test -- --coverage
        env:
          DATABASE_URL: postgresql://postgres:postgres@localhost:5432/testdb

      - name: Upload coverage
        uses: codecov/codecov-action@v4
        with:
          token: ${{ secrets.CODECOV_TOKEN }}
          files: ./coverage/lcov.info

Build & Docker in CI

  build-and-push:
    name: Build & Push Docker Image
    runs-on: ubuntu-latest
    needs: lint-and-test            # only run if tests pass
    if: github.ref == 'refs/heads/main'

    permissions:
      contents: read
      packages: write               # push to GitHub Container Registry

    steps:
      - uses: actions/checkout@v4

      - name: Log in to Container Registry
        uses: docker/login-action@v3
        with:
          registry: ${{ env.REGISTRY }}
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Extract metadata
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
          tags: |
            type=sha,prefix=,suffix=,format=short
            type=ref,event=branch
            type=semver,pattern={{version}}

      - name: Build and push
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=gha      # GitHub Actions cache
          cache-to: type=gha,mode=max
          build-args: |
            APP_VERSION=${{ github.sha }}

Secrets, Environments & Artifacts

  deploy-staging:
    name: Deploy to Staging
    runs-on: ubuntu-latest
    needs: build-and-push
    environment:
      name: staging
      url: https://staging.myapp.com

    steps:
      - name: Deploy to staging
        run: |
          curl -X POST ${{ secrets.DEPLOY_WEBHOOK_STAGING }} \
            -H 'Authorization: Bearer ${{ secrets.DEPLOY_TOKEN }}' \
            -d '{"image": "${{ env.IMAGE_NAME }}:${{ github.sha }}"}'

  # Upload/download build artifacts
  build:
    steps:
      - name: Build
        run: npm run build

      - name: Upload artifact
        uses: actions/upload-artifact@v4
        with:
          name: dist
          path: dist/
          retention-days: 7

  deploy:
    needs: build
    steps:
      - name: Download artifact
        uses: actions/download-artifact@v4
        with:
          name: dist
          path: dist/

      - name: Deploy to Vercel
        run: npx vercel --prod --token ${{ secrets.VERCEL_TOKEN }}

Matrix Builds & Reusable Workflows

# Matrix strategy — test across multiple versions
jobs:
  test:
    strategy:
      matrix:
        node: [18, 20, 22]
        os: [ubuntu-latest, windows-latest]
      fail-fast: false              # don't cancel others if one fails
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/setup-node@v4
        with:
          node-version: ${{ matrix.node }}
      - run: npm ci && npm test

# Reusable workflow — .github/workflows/deploy.yml
on:
  workflow_call:
    inputs:
      environment:
        required: true
        type: string
    secrets:
      DEPLOY_TOKEN:
        required: true

jobs:
  deploy:
    environment: ${{ inputs.environment }}
    runs-on: ubuntu-latest
    steps:
      - run: echo 'Deploying to ${{ inputs.environment }}'

# Caller workflow
jobs:
  deploy-prod:
    uses: ./.github/workflows/deploy.yml
    with:
      environment: production
    secrets:
      DEPLOY_TOKEN: ${{ secrets.DEPLOY_TOKEN }}