Docker Bridge Networks

Bridge networks are a type of networks used by dockerd(8).

Contents

Docker Bridge Networks

Default Network

By default, containers attach to bridge networks. See here to change that.

If a bridge network is not specified, the default network is used. This network is special in that there is no name resolution; the only way to communicate between containers is their ephemeral IP addresses.

Furthermore, the default network's use of IPv6 mandatorily matches the dockerd(8) configuration. See here to enable it.

Custom Networks

Custom bridge networks can be created like:

docker network create my-net

To enable IPv6 on a custom network, add the --ipv6 option.

Attaching Containers

A container can be created on a custom network by specifying the --network option.

docker run --detach --name my-nginx \
  --network=my-net \
  nginx:latest

A running container can be attached to a custom network like:

docker network connect my-net my-nginx

Containers on a custom bridge network can communicate with each other by addressing the containers' names. For example, the above container would be accessible at http://my-nginx.

$ docker run --interactive --tty --name my-alpine \
    --network=my-net \
    alpine:latest
# apk add curl
[ ... ]
# curl http://my-nginx
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
[ ... ]

Note that all ports are exposed.

Destroying Networks

Custom networks persist even when a container is stopped and destroyed.

To list all networks, try:

docker network ls

To delete a network, try:

docker network rm my-net

Note that a network cannot be destroyed if any containers are attached to it. They must be explicitly detached first.

docker network disconnect my-net my-nginx

Docker Compose

By default, Docker Compose creates a bridge network for all services defined in a compose file.

Given this compose file:

services:
  web:
    image: nginx
    ports:
      - "8000:80"
  db:
    image: postgres
    ports:
      - "8001:5432"

A bridge network named like myapp-default would be created
A container named web would be attached to that network and would be reachable within the network at http://web:80 or from the host at port 8000
A container named db would be attached to that network and would be reachable within the network at postgres://db:5432 or from the host at port 8001

Note that all ports are exposed within a bridge network.

This can create a need to review and manually delete networks on a recurring basis. See above for details.

Docker/BridgeNetworks