*
     * <p>This will be called at most once after all the services have entered the {@linkplain
     * State#RUNNING running} state. If any services fail during start up or {@linkplain
     * State#FAILED fail}/{@linkplain State#TERMINATED terminate} before all other services have
     * started {@linkplain State#RUNNING running} then this method will not be called.
     */

In this case, it would be better to get **one extra server** and run some processes on it so that they all have **enough RAM and CPU time**.

There's also the chance that for some reason you have a **spike** of usage of your API. Maybe it went viral, or maybe some other services or bots start using it. And you might want to have extra resources to be safe in those cases.

To see all the options you have, checkout <a href="https://docs.pydantic.dev/latest/concepts/types/" class="external-link" target="_blank">Pydantic's Type Overview</a>. You will see some examples in the next chapter.

For example, as in the `Image` model we have a `url` field, we can declare it to be an instance of Pydantic's `HttpUrl` instead of a `str`:

# Security - First Steps { #security-first-steps }

Let's imagine that you have your **backend** API in some domain.

And you have a **frontend** in another domain or in a different path of the same domain (or in a mobile application).

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

But you still need to use `Path` for the `item_id` path parameter. And you don't want to use `Annotated` for some reason.

Python will complain if you put a value with a "default" before a value that doesn't have a "default".

But you can re-order them, and have the value without a default (the query parameter `q`) first.

What inspired **FastAPI**, how it compares to alternatives and what it learned from them.

## Intro { #intro }

**FastAPI** wouldn't exist if not for the previous work of others.

There have been many tools created before that have helped inspire its creation.

I have been avoiding the creation of a new framework for several years. First I tried to solve all the features covered by **FastAPI** using many different frameworks, plug-ins, and tools.

{% endif %}

{% endfor %}

</div>

## Top Contributors

Here are the **Top Contributors**. 👷

These users have [created the most Pull Requests](help-fastapi.md#create-a-pull-request){.internal-link target=_blank} that have been *merged*.

They have contributed source code, documentation, etc. 📦

<div class="user-list user-list-center">

{% for user in (contributors.values() | list)[:50] %}

                "tearDownTwo should have been run before tearDownOne", false, tearDownOne.ran);
          }
        };

    SimpleTearDown tearDownTwo = new SimpleTearDown(callback);
    stack.addTearDown(tearDownTwo);

    assertEquals(false, tearDownOne.ran);
    assertEquals(false, tearDownTwo.ran);

    stack.runTearDown();

    assertEquals("tearDownOne should have run", true, tearDownOne.ran);

* **Uvicorn**:
    * Will have the best performance, as it doesn't have much extra code apart from the server itself.

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

{* ../../docs_src/openapi_callbacks/tutorial001.py hl[16:18,21:22,28:32] *}

There are 2 main differences from a normal *path operation*: