About Docker Compose

Docker Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application's services, networks, and volumes. Then, with a single command, you create and start all the services from your configuration.

Basic Structure

A docker-compose.yml file consists of several top-level sections:

services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./html:/usr/share/nginx/html

volumes:
  db_data:
    driver: local

networks:
  frontend:
  backend:
    driver: bridge

Common Mistakes

services:
  web:
    port: "80:80"  # Wrong!

services:
  web:
    ports:  # Correct!
      - "80:80"

services:
  web:
    volume: "./data:/data"  # Wrong!

services:
  web:
    volumes:  # Correct!
      - "./data:/data"

Best Practices

• Pin image versions: Use nginx:1.21 instead of nginx:latest
• Use environment files: Store secrets in .env files (add to .gitignore)
• Limit resources: Set memory and CPU limits for production
• Health checks: Define health checks for services
• Logging configuration: Configure log drivers and rotation
• Named volumes: Use named volumes for data that needs to persist
• Networking: Create separate networks for frontend and backend services

Complete Example

version: '3.8'

services:
  web:
    image: nginx:1.21
    ports:
      - "80:80"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./html:/usr/share/nginx/html:ro
    depends_on:
      - api
    networks:
      - frontend

  api:
    build: ./api
    environment:
      DATABASE_URL: postgres://user:pass@db:5432/mydb
    depends_on:
      - db
    networks:
      - frontend
      - backend

  db:
    image: postgres:13
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes:
      - db_data:/var/lib/postgresql/data
    networks:
      - backend

volumes:
  db_data:

networks:
  frontend:
  backend: