To create a custom Docker network driver, you need to write a Go plugin that implements the Network Driver Plugin API and communicate with Docker via Unix sockets. 1. First understand the basics of Docker plug-in, and the network driver runs as an independent process; 2. Set up the Go development environment and build an HTTP server that listens to Unix sockets; 3. Implement the required API methods such as Plugin.Activate, GetCapabilities, CreateNetwork, etc. and return the correct JSON response; 4. Register the plug-in in the /run/docker/plugins/ directory and test its functions through the docker network create command.

Creating a custom Docker network driver isn't something most users need to do, but if you're building specialized infrastructure or integrating with your own networking tools, it can be useful. The short version: you write a plugin in Go that implements Docker's Network Driver Plugin API , then register and use it like any other network driver.

Here's how to actually pull it off.

1. Understand the basics of Docker plugins

Docker supports several types of plugins — volume, network, authorization, etc. For custom networks, you're working with network drivers . These run as separate processes and communicate with Docker via a Unix socket using the Remote API .

What this means for you:

• You'll build a standalone binary (often written in Go)
• It needs to respond to specific JSON-based HTTP requests
• It should register itself under /run/docker/plugins/

You don't plug into Docker directly — you're essentially running a mini-service that Docker talks to when it needs to manage containers' networks.

2. Set up your development environment

Before writing code, make sure you have:

• Go installed (preferably recent version)
• Docker installed locally for testing
• Basic familiarity with Go modules

The official libnetwork pluginrpc package provides some tooling, but it's not mandatory. You can also just implement the expected JSON endpoints manually.

Here's what a basic setup might include:

• A main.go file that starts an HTTP server listening on a Unix socket
• Handlers for Docker's expected calls like Create , Join , Leave , etc.
• Logging so you can debug what Docker is asking for

If you're new to Go, start by writing a simple HTTP server that responds to GET requests — that way you can verify Docker sees your plugin before diving into the full spec.

3. Implement the required API methods

Docker expects your plugin to respond to certain HTTP routes. At minimum, you'll need to handle:

• /Plugin.Activate – tells Docker what kind of plugin this is ( {"Implements":["NetworkDriver"]} )
• /NetworkDriver.GetCapabilities – whether your driver supports things like remote subnets or multi-host
• /NetworkDriver.CreateNetwork – called when someone creates a network using your driver
• /NetworkDriver.DeleteNetwork
• /NetworkDriver.Join – container joins a network
• /NetworkDriver.Leave

Each method must return a well-formed JSON response, even if it's just {} . If you fail to implement one of these, Docker will refund to use your driver.

Some tips:

• Use structs to parse incoming JSON payloads
• Log every request so you can see what Docker is doing
• Start small — stub out all methods first, then flesh them out

4. Register and test your plugin

Once your plugin is running, Docker needs to find it. Place a .sock file in /run/docker/plugins/ — that's where Docker looks for plugins by default. Also create a .json file there if needed (though newer versions rely more on activation responses).

To test:

 docker network create --driver your-driver-name testnet

If Docker complains about missing capabilities or unsupported operations, check which methods you've implemented and what they return.

Also keep an eye on your logs — Docker won't tell you if your plugin crashes, only that it couldn't reach it.

Final notes

Writing a real production-ready network driver involves handling IPAM (IP Address Management), setting up actual network interfaces, routing, firewall rules, and more. But for a minimum proof of concept? Just getting Docker to accept your plugin and create a dummy network is a solid first step.

If you're doing this for learning purposes, go ahead and try implementing just the activation and capability methods first. Once Docker recognizes your plugin, you can slowly add support for each operation.

Basically that's it.

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