Docker Compose

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications using a YAML configuration file.

Basic Example

version: '3.8'

services:
  web:
    image: nginx:alpine
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html
  
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production

Full Stack Application

version: '3.8'

services:
  # Angular Frontend
  frontend:
    build:
      context: ./frontend
      dockerfile: Dockerfile
    ports:
      - "4200:80"
    depends_on:
      - api
    networks:
      - app-network
  
  # .NET API
  api:
    build:
      context: ./api
      dockerfile: Dockerfile
    ports:
      - "5000:80"
    environment:
      - ASPNETCORE_ENVIRONMENT=Production
      - ConnectionStrings__DefaultConnection=Server=sqlserver;Database=MyApp;User=sa;Password=YourPassword123
    depends_on:
      - sqlserver
      - redis
    networks:
      - app-network
  
  # Node.js Service
  service:
    build:
      context: ./service
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DATABASE_URL=postgresql://postgres:postgres@postgres:5432/myapp
      - MONGODB_URL=mongodb://mongodb:27017/myapp
      - REDIS_URL=redis://redis:6379
    depends_on:
      - postgres
      - mongodb
      - redis
    networks:
      - app-network
  
  # SQL Server
  sqlserver:
    image: mcr.microsoft.com/mssql/server:2022-latest
    environment:
      - ACCEPT_EULA=Y
      - SA_PASSWORD=YourPassword123
    ports:
      - "1433:1433"
    volumes:
      - sqlserver-data:/var/opt/mssql
    networks:
      - app-network
  
  # PostgreSQL
  postgres:
    image: postgres:15
    environment:
      - POSTGRES_DB=myapp
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres
    ports:
      - "5432:5432"
    volumes:
      - postgres-data:/var/lib/postgresql/data
    networks:
      - app-network
  
  # MongoDB
  mongodb:
    image: mongo:6
    ports:
      - "27017:27017"
    volumes:
      - mongo-data:/data/db
    networks:
      - app-network
  
  # Redis
  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"
    networks:
      - app-network

networks:
  app-network:
    driver: bridge

volumes:
  sqlserver-data:
  postgres-data:
  mongo-data:

Development Environment

version: '3.8'

services:
  app:
    build:
      context: .
      target: development
    volumes:
      - .:/app
      - /app/node_modules
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    command: npm run dev
  
  db:
    image: postgres:15
    environment:
      - POSTGRES_PASSWORD=postgres
    volumes:
      - dev-db:/var/lib/postgresql/data

volumes:
  dev-db:

Health Checks

services:
  api:
    image: myapi:latest
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:5000/health"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s
  
  postgres:
    image: postgres:15
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U postgres"]
      interval: 10s
      timeout: 5s
      retries: 5

Environment Files

# docker-compose.yml
services:
  app:
    env_file:
      - .env
      - .env.local

# .env
NODE_ENV=production
PORT=3000
DATABASE_URL=postgresql://postgres:postgres@postgres:5432/myapp

Scaling

services:
  api:
    image: myapi:latest
    deploy:
      replicas: 3

# Scale service
docker-compose up -d --scale api=5

Override Files

# docker-compose.override.yml
version: '3.8'

services:
  app:
    environment:
      - DEBUG=true
    volumes:
      - .:/app

Commands

# Start services
docker-compose up

# Start in background
docker-compose up -d

# Build images
docker-compose build

# View logs
docker-compose logs
docker-compose logs -f service-name

# Stop services
docker-compose stop

# Remove containers
docker-compose down

# Remove containers and volumes
docker-compose down -v

# Execute command
docker-compose exec app sh

# Run one-off command
docker-compose run app npm test

CI/CD Integration

# GitHub Actions
name: Docker Compose CI

on: [push]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      
      - name: Start services
        run: docker-compose up -d
      
      - name: Wait for services
        run: sleep 30
      
      - name: Run tests
        run: docker-compose exec -T app npm test
      
      - name: Stop services
        run: docker-compose down

Interview Tips

• Explain Docker Compose: Multi-container orchestration
• Show configuration: Full-stack YAML example
• Demonstrate databases: Multiple database services
• Discuss networking: Service communication
• Mention volumes: Data persistence
• Show commands: Common operations

Summary

Docker Compose orchestrates multi-container applications using YAML configuration. Define services for frontend, backend, and databases. Use networks for service communication. Implement volumes for data persistence. Configure health checks. Support development and production environments. Essential for local development and testing.