Introduction to Docker Networking

It’s always the network!

Any time there’s an infrastructure problem, we always blame the network. Part of the reason is that networks are at the center of everything — no network, no app!

In the early days of Docker, networking was hard — really hard. These days, it’s almost a pleasure ;-)

In this chapter, we’ll look at the fundamentals of Docker networking. Things like the Container Network Model (CNM) and libnetwork. We’ll also get our hands dirty building some networks.

The TLDR

Docker runs applications inside of containers, and applications need to communicate over lots of different networks. This means Docker needs strong networking capabilities.

Fortunately, Docker has solutions for container-to-container networks, as well as connecting to existing networks and VLANs. The latter is important for containerized apps that interact with functions and services on external systems such as VM’s and physical servers.

Docker networking is based on an open-source pluggable architecture called the Container Network Model (CNM). libnetwork is Docker’s real-world implementation of the CNM, and it provides all of Docker’s core networking capabilities. Drivers plug into libnetwork to provide specific network topologies.

To create a smooth out-of-the-box experience, Docker ships with a set of native drivers that deal with the most common networking requirements. These include single-host bridge networks, multi-host overlays, and options for plugging into existing VLANs. Ecosystem partners can extend things further by providing their own drivers.

Last but not least, libnetwork provides a native service discovery and basic container load balancing solution.

That’s this big picture. Let’s get into the details.