Now, let's imagine your organization gave you the `app/internal/admin.py` file.

It contains an `APIRouter` with some admin *path operations* that your organization shares between several projects.

For this example it will be super simple. But let's say that because it is shared with other projects in the organization, we cannot modify it and add a `prefix`, `dependencies`, `tags`, etc. directly to the `APIRouter`:

```

</div>

!!! tip
    With `passlib`, you could even configure it to be able to read passwords created by **Django**, a **Flask** security plug-in or many others.

    So, you would be able to, for example, share the same data from a Django application in a database with a FastAPI application. Or gradually migrate a Django application using the same database.

And multiple processes normally **don't share any memory**. This means that each running process has its own things, variables, and memory. And if you are consuming a large amount of memory in your code, **each process** will consume an equivalent amount of memory.

        * [Better with `Annotated`](https://fastapi.tiangolo.com/tutorial/path-params-numeric-validations/#better-with-annotated)
    * [Dependencies - First Steps - Share `Annotated` dependencies](https://fastapi.tiangolo.com/tutorial/dependencies/#share-annotated-dependencies)

This is very useful when you need to:

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps

This can be very useful for setting up **resources** that you need to use for the whole app, and that are **shared** among requests, and/or that you need to **clean up** afterwards. For example, a database connection pool, or loading a shared machine learning model.

## Use Case

Let's start with an example **use case** and then see how to solve it with this.

## Caveat

If you need to perform heavy background computation and you don't necessarily need it to be run by the same process (for example, you don't need to share memory, variables, etc), you might benefit from using other bigger tools like <a href="https://docs.celeryq.dev" class="external-link" target="_blank">Celery</a>.

#### Docker Compose

You could be deploying to a **single server** (not a cluster) with **Docker Compose**, so you wouldn't have an easy way to manage replication of containers (with Docker Compose) while preserving the shared network and **load balancing**.

Then you could want to have **a single container** with a **process manager** starting **several worker processes** inside.

#### Prometheus and Other Reasons

* `lt`: `l`ess `t`han
* `le`: `l`ess than or `e`qual

!!! info
    `Query`, `Path`, and other classes you will see later are subclasses of a common `Param` class.

    All of them share the same parameters for additional validation and metadata you have seen.

!!! note "Technical Details"
    When you import `Query`, `Path` and others from `fastapi`, they are actually functions.