---
title: Extension architecture
linkTitle: Architecture
description: Docker extension architecture
keywords: Docker, extensions, sdk, metadata
aliases:
- /desktop/extensions-sdk/architecture/
weight: 50
---
Extensions are applications that run inside the Docker Desktop. They're packaged as Docker images, distributed
through Docker Hub, and installed by users either through the Marketplace within the Docker Desktop Dashboard or the
Docker Extensions CLI.
Extensions can be composed of three (optional) components:
- A frontend (or User Interface): A web application displayed in a tab of the dashboard in Docker Desktop
- A backend: One or many containerized services running in the Docker Desktop VM
- Executables: Shell scripts or binaries that Docker Desktop copies on the host when installing the extension
An extension doesn't necessarily need to have all these components, but at least one of them depending on the extension features.
To configure and run those components, Docker Desktop uses a `metadata.json` file. See the
[metadata](metadata) section for more details.
## The frontend
The frontend is basically a web application made from HTML, Javascript, and CSS. It can be built with a simple HTML
file, some vanilla Javascript or any frontend framework, such as React or Vue.js.
When Docker Desktop installs the extension, it extracts the UI folder from the extension image, as defined by the
`ui` section in the `metadata.json`. See the [ui metadata section](metadata.md#ui-section) for more details.
Every time users click on the **Extensions** tab, Docker Desktop initializes the extension's UI as if it was the first time. When they navigate away from the tab, both the UI itself and all the sub-processes started by it (if any) are terminated.
The frontend can invoke `docker` commands, communicate with the extension backend, or invoke extension executables
deployed on the host, through the [Extensions SDK](https://www.npmjs.com/package/@docker/extension-api-client).
> [!TIP]
>
> The `docker extension init` generates a React based extension. But you can still use it as a starting point for
> your own extension and use any other frontend framework, like Vue, Angular, Svelte, etc. or event stay with
> vanilla Javascript.
Learn more about [building a frontend](/manuals/extensions/extensions-sdk/build/frontend-extension-tutorial.md) for your extension.
## The backend
Alongside a frontend application, extensions can also contain one or many backend services. In most cases, the Extension does not need a backend, and features can be implemented just by invoking docker commands through the SDK. However, there are some cases when an extension requires a backend
service, for example:
- To run long-running processes that must outlive the frontend
- To store data in a local database and serve them back with a REST API
- To store the extension state, like when a button starts a long-running process, so that if you navigate away
from the extension and come back, the frontend can pick up where it left off
- To access specific resources in the Docker Desktop VM, for example by mounting folders in the compose
file
> [!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.