# Backend Services

Outline's backend is split into several distinct [services](../server/services)
that combined form the application. When running the official Docker container
it will run all of the production services by default.

You can choose which services to run through either a comma separated CLI flag,
`--services`, or the `SERVICES` environment variable. For example:

```bash
yarn start --services=web,worker
```

## Admin

Currently this service is only used in development to view and debug the queues.
It is hosted at `/admin`.

## Web

The web server hosts the Application and API, as such this is the main service
and must be run by at least one process.

## Websockets

The websocket server is used to communicate with the frontend, it can be ran on
the same box as the web server or separately.

## Worker

At least one worker process is required to process the [queues](../server/queues).

## Collaboration

The service is in alpha and as such is not started by default. It must run
separately to the `websockets` service, and will not start in the same process.
The `COLLABORATION_URL` must be set to the publicly accessible URL when running
the service. For example, if the app is hosted at `https://docs.example.com` you
may use something like: `COLLABORATION_URL=wss://docs-collaboration.example.com`.

Start the service with:

```bash
yarn start --services=collaboration
```