These examples run the server program (e.g Uvicorn), starting **a single process**, listening on all the IPs (`0.0.0.0`) on a predefined port (e.g. `80`).

This is the basic idea. But you will probably want to take care of some additional things, like:

* Security - HTTPS
* Running on startup
* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

<img src="/img/tutorial/behind-a-proxy/image02.png">

Right as we wanted it. ✔️

This is because FastAPI uses this `root_path` to create the default `server` in OpenAPI with the URL provided by `root_path`.

## Additional servers

!!! warning
    This is a more advanced use case. Feel free to skip it.

By default, **FastAPI** will create a `server` in the OpenAPI schema with the URL for the `root_path`.

## 0.12.0

* Add additional `responses` parameter to *path operation decorators* to extend responses in OpenAPI (and API docs).
    * It also allows extending existing responses generated from `response_model`, declare other media types (like images), etc.
    * The new documentation is here: [Additional Responses](https://fastapi.tiangolo.com/advanced/additional-responses/).

    - tutorial/debugging.md
  - Advanced User Guide:
    - advanced/index.md
    - advanced/path-operation-advanced-configuration.md
    - advanced/additional-status-codes.md
    - advanced/response-directly.md
    - advanced/custom-response.md
    - advanced/additional-responses.md
    - advanced/response-cookies.md
    - advanced/response-headers.md
    - advanced/response-change-status-code.md

* Used in production applications.

## Starlette features

**FastAPI** is fully compatible with (and based on) <a href="https://www.starlette.io/" class="external-link" target="_blank"><strong>Starlette</strong></a>. So, any additional Starlette code you have, will also work.

`FastAPI` is actually a sub-class of `Starlette`. So, if you already know or use Starlette, most of the functionality will work the same way.

**Tutorial - User Guide** (what you are reading right now).

It's designed so that you can build a complete application with just the **Tutorial - User Guide**, and then extend it in different ways, depending on your needs, using some of the additional ideas from the **Advanced User Guide**....

The same way as with Pydantic models, you declare class attributes with type annotations, and possibly default values.

You can use all the same validation features and tools you use for Pydantic models, like different data types and additional validations with `Field()`.

=== "Pydantic v2"

    ```Python hl_lines="2  5-8  11"
    {!> ../../../docs_src/settings/tutorial001.py!}
    ```

=== "Pydantic v1"

    !!! info