What is a network containerization module in Docker?

The Container Network Module (CNM) is a Docker specification that defines the interaction model between containers and the external world. It consists of three main primitives:

• Sandbox: The container's network stack, including its interfaces, routing tables, and DNS.
• Endpoint: The connection point of the Sandbox to the Network.
• Network: A network segment to which Endpoints can connect. Containers within the same Network can communicate with each other.

CNM provides a plugin interface that allows various drivers to implement network functions. Docker Engine manages Sandboxes and Endpoints, while network drivers are responsible for creating and configuring Networks.

Examples of built-in Docker network drivers:

• bridge: Creates a NAT network for containers to communicate with each other and the outside world through the host IP.
• host: The container uses the host's network stack directly.
• none: The container has no network interface.
• overlay: Creates a distributed network across multiple Docker hosts for swarm services.

Example of creating a bridge network:

docker network create my_bridge_network

Connecting a container to this network:

docker run -d --network my_bridge_network nginx