---
title: Add a backend to your extension
description: Learn how to add a backend to your extension.
keywords: Docker, extensions, sdk, build
aliases:
 - /desktop/extensions-sdk/tutorials/minimal-backend-extension/
 - /desktop/extensions-sdk/build/minimal-backend-extension/
 - /desktop/extensions-sdk/build/set-up/backend-extension-tutorial/
 - /desktop/extensions-sdk/build/backend-extension-tutorial/
---

Your extension can ship a backend part with which the frontend can interact with. This page provides information on why and how to add a backend.

Before you start, make sure you have installed the latest version of [Docker Desktop](https://www.docker.com/products/docker-desktop/).

> Tip
>
> Check the [Quickstart guide](../quickstart.md) and `docker extension init <my-extension>`. They provide a better base for your extension as it's more up-to-date and related to your install of Docker Desktop.

## Why add a backend?

Thanks to the Docker Extensions SDK, most of the time you should be able to do what you need from the Docker CLI
directly from [the frontend](frontend-extension-tutorial.md#use-the-extension-apis-client).

Nonetheless, there are some cases where you might need to add a backend to your extension. So far, extension
builders have used the backend to:
- Store data in a local database and serve them back with a REST API.
- Store the extension state, for example when a button starts a long-running process, so that if you navigate away from the extension user interface and comes back, the frontend can pick up where it left off.

For more information about extension backends, see [Architecture](../architecture/_index.md#the-backend).

## Add a backend to the extension

If you created your extension using the `docker extension init` command, you already have a backend setup. Otherwise, you have to first create a `vm` directory that contains the code and updates the Dockerfile to
containerize it.

Here is the extension folder structure with a backend:

```bash
.
├── Dockerfile # (1)
├── Makefile
├── metadata.json
├── ui
    └── index.html
└── vm # (2)
    ├── go.mod
    └── main.go
```

1. Contains everything required to build the backend and copy it in the extension's container filesystem.
2. The source folder that contains the backend code of the extension.

Although you can start from an empty directory or from the `vm-ui extension` [sample](https://github.com/docker/extensions-sdk/tree/main/samples),
it is highly recommended that you start from the `docker extension init` command and change it to suit your needs.

> [!TIP]
>
> The `docker extension init` generates a Go backend. But you can still use it as a starting point for
> your own extension and use any other language like Node.js, Python, Java, .Net, or any other language and framework.

In this tutorial, the backend service simply exposes one route that returns a JSON payload that says "Hello".

```json
{ "Message": "Hello" }
```

> [!IMPORTANT]
>
> We recommend that, the frontend and the backend communicate through sockets, and named pipes on Windows, instead of
> HTTP. This prevents port collision with any other running application or container running
> on the host. Also, some Docker Desktop users are running in constrained environments where they
> can't open ports on their machines. When choosing the language and framework for your backend, make sure it
> supports sockets connection.

{{< tabs group="lang" >}}
{{< tab name="Go" >}}

```go
package main

import (
	"flag"
	"log"
	"net"
	"net/http"
	"os"

	"github.com/labstack/echo"
	"github.com/sirupsen/logrus"
)

func main() {
	var socketPath string
	flag.StringVar(&socketPath, "socket", "/run/guest/volumes-service.sock", "Unix domain socket to listen on")
	flag.Parse()

	os.RemoveAll(socketPath)

	logrus.New().Infof("Starting listening on %s\n", socketPath)
	router := echo.New()
	router.HideBanner = true

	startURL := ""

	ln, err := listen(socketPath)
	if err != nil {
		log.Fatal(err)
	}
	router.Listener = ln