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Docker – What is a Docker network?

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As you already know, a network is a linkage system that allows computers and other hardware devices to communicate. A Docker network is the same thing. It is a linkage system that allows Docker containers to communicate with each other on the same Docker host, or with containers, computers, and hardware outside of the container’s host, including containers running on other Docker hosts.

If you are familiar with the cloud computing analogy of pets versus cattle, you understand the necessity of being able to manage resources at scale. Docker networks allow you to do just that. They abstract away most of the complexity of networking, delivering easy-to-understand, easy-to-document, and easy-to-use networks for your containerized apps. The Docker network is based on a standard, created by Docker, called the Container Network Model (CNM). There is a competing networking standard, created by CoreOS, called the Container Network Interface (CNI). The CNI standard has been adopted by several projects, most notably Kubernetes, and arguments can be made to support its use. However, in this chapter, we will focus our attention on the CNM standard from Docker.

The CNM has been implemented by the libnetwork project, and you can learn more about that project by following the link in the references for this section. The CNM implementation, written in Go, is made up of three constructs: the sandbox, the endpoint, and the network. The sandbox is a network namespace. Each container has its own sandbox. It holds the configuration of the container’s network stack. This includes its routing tables, interfaces, and DNS settings for IP and MAC addresses. The sandbox also contains the network endpoints for the container. Next, the endpoints are what join the sandbox to networks. Endpoints are essentially network interfaces, such as eth0. A container’s sandbox may have more than one endpoint, but each endpoint will connect to only a single network. Finally, a network is a collection of connected endpoints, which allow communication between connections. Every network has a name, an address space, an ID, and a network type.

Libnetwork is a pluggable architecture that allows network drivers to implement the specifics for the components we just described. Each network type has its own network driver. Docker provides built-in drivers. These default, or local, drivers include the bridge driver and the overlay driver. In addition to the built-in drivers, libnetwork supports third-party-created drivers. These drivers are referred to as remote drivers. Some examples of remote drivers include Calico, Contiv, and Weave.

You now know a little about what a Docker network is, and after reading these details, you might be thinking, where’s the easy that he talked about? Hang in there. now we are going to start discussing how easy it is for you to create and use Docker networks. As with Docker volume, the network commands represent their own management category. As you would expect, the top-level management command for network is as follows:

# Docker network managment command
docker network 

The subcommands available in the network management group include the following:

# Docker network management subcommands
docker network connect           # Connect a container to a network
docker network create            # Create a network
docker network disconnect        # Disconnect a container from a network
docker network inspect           # Display network details
docker network ls                # List networks
docker network rm                # Remove one or more networks
docker network prune             # Remove all unused networks

Let’s now take a look at the built-in or local network drivers.

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