When you install FastAPI with something like `pip install fastapi` you already get `uvicorn[standard]` as well.

=== "Hypercorn"

    * <a href="https://gitlab.com/pgjones/hypercorn" class="external-link" target="_blank">Hypercorn</a>, an ASGI server also compatible with HTTP/2.

    <div class="termy">

    The current version assumes Pydantic v1.

    The new docs will include Pydantic v2 and will use <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a> once it is updated to use Pydantic v2 as well.

!!! warning "Deprecated"
    This tutorial is deprecated and will be removed in a future version.

# OpenAPI Webhooks

There are cases where you want to tell your API **users** that your app could call *their* app (sending a request) with some data, normally to **notify** of some type of **event**.

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps

    * Numbers (`int`, `float`) with min and max values, etc.

* Validation for more exotic types, like:
    * URL.
    * Email.
    * UUID.
    * ...and others.

All the validation is handled by the well-established and robust **Pydantic**.

### Security and authentication

Security and authentication integrated. Without any compromise with databases or data models.

!!! info
    If you are using containers, for example with Docker or Kubernetes, I'll tell you more about that in the next chapter: [FastAPI in Containers - Docker](docker.md){.internal-link target=_blank}.

    In particular, when running on **Kubernetes** you will probably **not** want to use Gunicorn and instead run **a single Uvicorn process per container**, but I'll tell you about it later in that chapter.

## Gunicorn with Uvicorn Workers