> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pysquirrels.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Mount to existing FastAPI app

> Learn how to integrate Squirrels APIs into an existing FastAPI application

Sometimes you might want to integrate Squirrels APIs into an existing FastAPI application rather than running Squirrels as a standalone server (i.e., using [sqrl run](/references/cli/run)). This allows you to serve your Squirrels datasets alongside other routes and services in your application.

## Prerequisites

* A Squirrels project already initialized and configured, with `squirrels >= 0.6.0` installed.
* An existing FastAPI application in Python.

## Steps

### 1. Initialize SquirrelsProject and get components

First, you need to create an instance of `SquirrelsProject` pointing to your project directory and use it to retrieve the FastAPI components. We recommend using a `with` statement to ensure that the project is closed and its resources are released after use.

```python theme={null}
from fastapi import FastAPI
from squirrels import SquirrelsProject

# Initialize the project and get the FastAPI components
with SquirrelsProject(project_path="./my_squirrels_project") as sqrl_proj:
    sqrl_server = sqrl_proj.get_fastapi_components(host="localhost", port=8000)
```

<Note>
  The `host` and `port` arguments are optional and only used for the welcome banner. Squirrels does not get to control or view the host and port of the API server - only uvicorn gets to control these. If not provided, the default values of `localhost` and `8000` are used.
</Note>

The `sqrl_server` is a [FastAPIComponents] object that contains:

* `fastapi_app`: The sub-app containing all the routes for your Squirrels datasets, dashboards, and authentication.
* `lifespan`: The lifespan context manager that handles background tasks such as periodically refreshing parameter options from data sources.
* `mount_path`: The mount path for the Squirrels sub-app.

<Note>
  By default, the mount path is `/analytics/{project_name}/v{project_version}`. You can specify the `mount_path_format` argument to customize the mount path with your own format while including the project name and version.

  Note that any underscores in the project name are replaced by dashes. For example, if the project name is "my\_project" and the project version is "1", then the `mount_path` value is `/analytics/my-project/v1`.
</Note>

### 2. Integrate the lifespan

Create the FastAPI app with the Squirrels lifespan.

```python theme={null}
app = FastAPI(lifespan=sqrl_server.lifespan)
```

If you have defined your own lifespan function, you should include the Squirrels lifespan to ensure that Squirrels' background tasks run correctly.

```python theme={null}
from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app: FastAPI):
    # Squirrels lifespan context manager
    async with sqrl_server.lifespan(sqrl_server.fastapi_app):
        yield

# Create the main app with the lifespan
app = FastAPI(lifespan=lifespan)
```

### 3. Mount the sub-app

Mount the Squirrels sub-app to your main FastAPI application at the mount path of the [FastAPIComponents] object.

```python theme={null}
# Mount the Squirrels sub-app
app.mount(sqrl_server.mount_path, sqrl_server.fastapi_app)
```

## Complete Example

Here is a complete example of a FastAPI application with a Squirrels project mounted.

```python theme={null}
from fastapi import FastAPI
from squirrels import SquirrelsProject

# 1. Initialize Squirrels project and get FastAPI components
with SquirrelsProject(project_path=".") as sqrl_proj:
    sqrl_server = sqrl_proj.get_fastapi_components(host="localhost", port=8000)

    # 2. Create main app
    app = FastAPI(lifespan=sqrl_server.lifespan)

    @app.get("/")
    async def root():
        return {"message": "Hello from the main app!"}

    # 3. Mount the Squirrels sub-app
    app.mount(sqrl_server.mount_path, sqrl_server.fastapi_app)

    if __name__ == "__main__":
        import uvicorn
        uvicorn.run(app, host="0.0.0.0", port=8000, proxy_headers=True, forwarded_allow_ips="*")
```

Now, your Squirrels APIs will be available under the path `sqrl_server.mount_path` (e.g., `http://localhost:8000/analytics/my-project/v1/api/0/...`).

[FastAPIComponents]: /references/python/types/fastapicomponents