DockerHow-ToBeginner · 4 min read

How to Use Networks in Docker Compose: Simple Guide

In docker-compose.yml, you define networks under the networks key and assign them to services using the networks property. This lets containers communicate on isolated or shared networks, improving organization and security.

📐

Syntax

The networks section defines custom networks. Each service can specify which networks it connects to under its networks key. You can set network driver options if needed.

Basic parts:

networks: top-level key to declare networks.
service_name: under services, lists networks the service uses.
Optional network config like driver to choose network type.

yaml

version: '3.8'
services:
  app:
    image: alpine
    networks:
      - mynet
networks:
  mynet:
    driver: bridge

💻

Example

This example shows two services connected to the same custom network called mynet. They can communicate by container name.

yaml

version: '3.8'
services:
  web:
    image: nginx
    networks:
      - mynet
  app:
    image: alpine
    command: ping -c 3 web
    networks:
      - mynet
networks:
  mynet:
    driver: bridge

Output

PING web (172.18.0.2): 56 data bytes 64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.123 ms 64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.110 ms 64 bytes from 172.18.0.2: seq=2 ttl=64 time=0.105 ms --- web ping statistics --- 3 packets transmitted, 3 packets received, 0% packet loss

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Common Pitfalls

Common mistakes include:

Not defining the network under networks but trying to use it in services.
Forgetting to connect all services that need to communicate to the same network.
Using default networks unintentionally, which can cause isolation issues.

Always explicitly define and assign networks for clear container communication.

yaml

version: '3.8'
services:
  app:
    image: alpine
    networks:
      - mynet
  db:
    image: mysql
    # Missing networks key here
networks:
  mynet:
    driver: bridge

# Corrected version:

version: '3.8'
services:
  app:
    image: alpine
    networks:
      - mynet
  db:
    image: mysql
    networks:
      - mynet
networks:
  mynet:
    driver: bridge

📊

Quick Reference

Key	Description
networks:	Top-level key to define custom networks
service_name.networks:	List of networks a service connects to
driver:	Network driver type, e.g., bridge, overlay
aliases:	Optional alternative names for containers on the network
external:	Use an existing external network instead of creating one

✅

Key Takeaways

Define custom networks under the top-level 'networks' key in docker-compose.yml.

Assign networks to services using the 'networks' property to enable container communication.

Use the 'driver' option to specify network type like 'bridge' or 'overlay'.

Always connect all communicating services to the same network explicitly.

Avoid relying on default networks to prevent unexpected isolation or conflicts.