author_link: https://newrelic.com
    link: https://newrelic.com/instant-observability/fastapi/e559ec64-f765-4470-a15f-1901fcebb468
    title: How to monitor FastAPI application performance using Python agent
  - author: Jean-Baptiste Rocher
    author_link: https://hashnode.com/@jibrocher
    link: https://dev.indooroutdoor.io/series/fastapi-react-poll-app
    title: Building the Poll App From Django Tutorial With FastAPI And React

# Deployment

Deploying a **FastAPI** application is relatively easy.

## What Does Deployment Mean

To **deploy** an application means to perform the necessary steps to make it **available to the users**.

For a **web API**, it normally involves putting it in a **remote machine**, with a **server program** that provides good performance, stability, etc, so that your **users** can **access** the application efficiently and without interruptions or problems.

This is similar to the 200 HTTP status codes (from 200 to 299). Those "200" status codes mean that somehow there was a "success" in the request.

The status codes in the 400 range mean that there was an error from the client.

Remember all those **"404 Not Found"** errors (and jokes)?

## Use `HTTPException`

Let's imagine that loading the model can **take quite some time**, because it has to read a lot of **data from disk**. So you don't want to do it for every request.

You could load it at the top level of the module/file, but that would also mean that it would **load the model** even if you are just running a simple automated test, then that test would be **slow** because it would have to wait for the model to load before being able to run an independent part of the code.

This was designed this way mainly to allow using the same objects "yielded" by dependencies inside of background tasks, because the exit code would be executed after the background tasks were finished.

Nevertheless, as this would mean waiting for the response to travel through the network while unnecessarily holding a resource in a dependency with yield (for example a database connection), this was changed in FastAPI 0.106.0.

!!! tip

    No será serializado con el modelo, etc.

    Asegúrate de que la respuesta tenga los datos que quieras, y que los valores sean JSON válidos (si estás usando `JSONResponse`).

!!! note "Detalles Técnicos"
    También podrías utilizar `from starlette.responses import JSONResponse`.

    * Los validadores también permiten que se definan fácil y claramente schemas complejos de datos. Estos son chequeados y documentados como JSON Schema.
    * Puedes tener objetos de **JSON profundamente anidados** y que todos sean validados y anotados.
* **Extensible**:

                    `response_model`, converting any data as necessary to generate the
                    corresponding JSON. But if the data in the object returned is not
                    valid, that would mean a violation of the contract with the client,
                    so it's an error from the API developer. So, FastAPI will raise an
                    error and return a 500 error code (Internal Server Error).

from fastapi import FastAPI

app = FastAPI()


@app.get("/users")
async def read_users():
    return ["Rick", "Morty"]


@app.get("/users")
async def read_users2():

[19515] [INFO] Started server process [19515]
[19515] [INFO] Waiting for application startup.
[19515] [INFO] Application startup complete.
```

</div>

Let's see what each of those options mean:

* `main:app`: This is the same syntax used by Uvicorn, `main` means the Python module named "`main`", so, a file `main.py`. And `app` is the name of the variable that is the **FastAPI** application.