If you have an API that does a comparable amount of computations every time and you have a lot of clients, then the **CPU utilization** will probably *also be stable* (instead of constantly going up and down quickly).

### Examples of Replication Tools and Strategies

There can be several approaches to achieve this, and I'll tell you more about specific strategies in the next chapters, for example when talking about Docker and containers.

you will have a more or less well-defined, stable, and limited amount of memory consumed by each of those containers (more than one if they are replicated).

And then you can set those same memory limits and requirements in your configurations for your container management system (for example in **Kubernetes**). That way it will be able to **replicate the containers** in the **available machines** taking into account the amount of memory needed by them, and the amount available in the machines...

It would take the same amount of time to finish with or without turns (concurrency) and you would have done the same amount of work.

```Python hl_lines="9"
{!../../../docs_src/behind_a_proxy/tutorial004.py!}
```

and then it won't include it in the OpenAPI schema.

## Mounting a sub-application

If you need to mount a sub-application (as described in [Sub Applications - Mounts](sub-applications.md){.internal-link target=_blank}) while also using a proxy with `root_path`, you can do it normally, as you would expect.

    return form_data


@app.get("/users/me")
def read_users_me(current_user: Optional[User] = Depends(get_current_user)):
    if current_user is None:
        return {"msg": "Create an account first"}
    return current_user


client = TestClient(app)


def test_security_oauth2():
    response = client.get("/users/me", headers={"Authorization": "Bearer footokenbar"})

    * That's one layer **below HTTP**.
    * So, the **certificate and encryption** handling is done **before HTTP**.
* **TCP doesn't know about "domains"**. Only about IP addresses.
    * The information about the **specific domain** requested goes in the **HTTP data**.
* The **HTTPS certificates** "certify" a **certain domain**, but the protocol and encryption happen at the TCP level, **before knowing** which domain is being dealt with.

For example, you could identify a "car" or a "blog post".

Then you could add permissions about that entity, like "drive" (for the car) or "edit" (for the blog).

And then, you could give that JWT token to a user (or bot), and they could use it to perform those actions (drive the car, or edit the blog post) without even needing to have an account, just with the JWT token your API generated for that.

    The second version is an "absolute import":

    ```Python
    from app.routers import items, users
    ```

    To learn more about Python Packages and Modules, read <a href="https://docs.python.org/3/tutorial/modules.html" class="external-link" target="_blank">the official Python documentation about Modules</a>.

### Avoid name collisions

We are importing the submodule `items` directly, instead of importing just its variable `router`.

    * Read other ideas, articles, and read about tools I have created.
    * Follow me to read when I publish something new.

## Tweet about **FastAPI**

<a href="https://twitter.com/compose/tweet?text=I'm loving @fastapi because... https://github.com/tiangolo/fastapi" class="external-link" target="_blank">Tweet about **FastAPI**</a> and let me and others know why you like it. 🎉

!!! tip
    Pydantic, which is what powers all the data validation and serialization in FastAPI, has a special behavior when you use `Optional` or `Union[Something, None]` without a default value, you can read more about it in the Pydantic docs about <a href="https://docs.pydantic.dev/latest/concepts/models/#required-optional-fields" class="external-link" target="_blank">Required Optional fields</a>.

!!! tip