docker-compose-networking

# Docker Compose Networking

Master network configuration and service communication patterns in Docker Compose for building secure, scalable multi-container applications.

## Default Bridge Network

Docker Compose automatically creates a default bridge network for all services in a compose file:

```yaml
version: '3.8'

services:
  frontend:
    image: nginx:alpine
    ports:
      - "80:80"
    # Can reach backend using service name as hostname

  backend:
    image: node:18-alpine
    command: node server.js
    # Accessible at hostname 'backend' from frontend

  database:
    image: postgres:15-alpine
    environment:
      POSTGRES_PASSWORD: secret
    # Accessible at hostname 'database' from backend
```

In this setup:

- All services can communicate using service names as hostnames
- Frontend can reach backend at `http://backend:3000`
- Backend can reach database at `postgres://database:5432`
- Only frontend's port 80 is exposed to host

## Custom Bridge Networks

Define custom networks for service isolation and segmentation:

```yaml
version: '3.8'

services:
  frontend:
    image: nginx:alpine
    networks:
      - frontend-network
    ports:
      - "80:80"

  api:
    image: node:18-alpine
    networks:
      - frontend-network
      - backend-network
    environment:
      DATABASE_URL: postgresql://db:5432/app

  database:
    image: postgres:15-alpine
    networks:
      - backend-network
    environment:
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: app
    volumes:
      - db-data:/var/lib/postgresql/data

  cache:
    image: redis:7-alpine
    networks:
      - backend-network
    command: redis-server --appendonly yes
    volumes:
      - redis-data:/data

networks:
  frontend-network:
    driver: bridge
  backend-network:
    driver: bridge
    internal: true

volumes:
  db-data:
  redis-data:
```

Network isolation:

- Frontend can only reach API
- Frontend cannot reach database or cache directly
- API can reach all services
- Backend network