Docker supports creating virtual bridge networks between containers. Remember that a Docker container has many of the features of an installed Linux OS. Each container can have its own IP address(es) and exposed ports. Docker supports creating what amounts to being a virtual Ethernet segment, called a bridge network. These networks live solely within the host computer and, by default, are not reachable by anything outside the host computer.

A Docker bridge network, therefore, has strictly limited access. Any Docker container attached to a bridge network can communicate with other containers attached to that network. The containers find each other by hostname, and Docker includes an embedded DNS server to set up the hostnames required. That DNS server is configured to not require dots in domain names, meaning that the DNS/hostname of each container is simply the container name, rather than something such as container-name.service. This policy of using hostnames to identify containers is Docker's implementation of service discovery.

Create a directory named authnet as a sibling to the users and notes directories. We'll be working on AuthNet in that directory.

Create a file, buildauthnet.sh, containing the following:

docker network create --driver bridge authnet

Type the following:

$ sh -x buildauthnet.sh
+ docker network create --driver bridge authnet 
3021e2069278c2acb08d94a2d31507a43f089db1c02eecc97792414b498eb785

This creates a Docker bridge network.