27. Compose Networking

1services:
2  web:
3    # Can reach 'db' by hostname
4    environment:
5      - DATABASE_HOST=db
6  db:
7    image: postgres

1services:
2  web:
3    networks:
4      - frontend
5      - backend
6
7  api:
8    networks:
9      - backend
10
11  db:
12    networks:
13      - backend
14
15networks:
16  frontend:
17  backend:

1networks:
2  existing-network:
3    external: true
4
5services:
6  web:
7    networks:
8      - existing-network

1services:
2  db:
3    networks:
4      backend:
5        aliases:
6          - database
7          - postgres