```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

!!! tip
    Notice that even though you are accessing it at `http://127.0.0.1:8000/app` it shows the `root_path` of `/api/v1`, taken from the option `--root-path`.

But if your connection to the server is lost, the **running process** will probably die.

And if the server is restarted (for example after updates, or migrations from the cloud provider) you probably **won't notice it**. And because of that, you won't even know that you have to restart the process manually. So, your API will just stay dead. 😱

### Run Automatically on Startup

!!! info
    The `app.webhooks` object is actually just an `APIRouter`, the same type you would use when structuring your app with multiple files.

    "paid": true
}
```

and it would expect a response from that *external API* with a JSON body like:

```JSON
{
    "ok": true
}
```

!!! tip
    Notice how the callback URL used contains the URL received as a query parameter in `callback_url` (`https://www.external.org/events`) and also the invoice `id` from inside of the JSON body (`2expen51ve`).

### Add the callback router

And to communicate using WebSockets with your backend you would probably use your frontend's utilities.

Or you might have a native mobile application that communicates with your WebSocket backend directly, in native code.

Or you might have any other way to communicate with the WebSocket endpoint.

---

participant dep as Dep with yield
participant operation as Path Operation
participant tasks as Background tasks

    Note over client,tasks: Can raise exception for dependency, handled after response is sent
    Note over client,operation: Can raise HTTPException and can change the response
    client ->> dep: Start request
    Note over dep: Run code up to yield
    opt raise
        dep -->> handler: Raise HTTPException

### The config file

Coming from the previous example, your `config.py` file could look like:

```Python hl_lines="10"
{!../../../docs_src/settings/app02/config.py!}
```

Notice that now we don't create a default instance `settings = Settings()`.

### The main app file

Now we create a dependency that returns a new `config.Settings()`.

=== "Python 3.9+"

* Build your FastAPI image:

<div class="termy">

```console
$ docker build -t myimage .

---> 100%
```

</div>

!!! tip
    Notice the `.` at the end, it's equivalent to `./`, it tells Docker the directory to use to build the container image.

    In this case, it's the same current directory (`.`).

### Start the Docker Container