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Create a FastAPI app

This recipe demonstrates how to create a simple FastAPI application that can be deployed on Databricks Apps.

Code structure​

Our FastAPI application will initially have the following structure:

FilePurpose
app.pyMain FastAPI application entrypoint
app.yamlDatabricks Apps deployment configuration
requirements.txtMain application dependencies
routes/__init__.pyModule initialisation for API-router
routes/v1/__init__.pySub-module initialisation for API-router (e.g. /api/v1/* routes)
routes/v1/healthcheck.pyIsolated code handler for healthcheck
tree -L 3
.
├── app.py
├── app.yaml
├── routes
│   ├── __init__.py
│   └── v1
│       ├── __init__.py
│       └── healthcheck.py
├── requirements.txt

Main application entrypoint​

app.py
from fastapi import FastAPI

from routes import api_router

app = FastAPI(
    title="FastAPI & Databricks Apps",
    description="A simple FastAPI application example for Databricks Apps runtime",
    version="1.0.0",
)

# Router assignment
app.include_router(api_router)

API routes​

warning

In order to use OAuth2 Bearer token authentication with Databricks Apps, your application code must provide valid routes with a prefix of /api.

Let's define the main router entrypoint for the application.

routes/__init__.py
from fastapi import APIRouter

# Import routers from versioned packages
from .v1 import router as v1_router

# Create a router for the API
api_router = APIRouter()

# Include versioned routers - prefix must have /api for Databricks Apps token-based auth
api_router.include_router(v1_router, prefix="/api/v1")

We then can define specific routers for the application, using versioning and specific endpoints for isolation per optimal practice.

Next, we can create a dedicated file to handle healthchecks, exposed via https://<app-url>/api/v1/healthcheck.

routes/v1/__init__.py
"""V1 API routes."""

from fastapi import APIRouter

from .healthcheck import router as healthcheck_router

router = APIRouter()

# Include endpoint-specific routers
router.include_router(healthcheck_router)
routes/v1/healthcheck.py
from datetime import datetime, timezone
from fastapi import APIRouter
from typing import Dict

router = APIRouter()

@router.get("/healthcheck")
async def healthcheck() -> Dict[str, str]:
    """Return the API status."""
    return {"status": "OK", "timestamp": datetime.now(timezone.utc).isoformat()}

Running the FastAPI application​

Local machine​

To run the application locally, use the following terminal command: uvicorn app:app --reload:

INFO:     Will watch for changes in these directories: ['/Users/user.name/home/databricks-apps-cookbook/fastapi']
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [56162] using StatReload
INFO:     Started server process [56164]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

Once the app is running, you will be to access the following endpoints:

Accessing the app or making changes to app.py will update the tailing application log in the terminal:

INFO:     127.0.0.1:54508 - "GET / HTTP/1.1" 200 OK
INFO:     127.0.0.1:58696 - "GET /docs HTTP/1.1" 200 OK
INFO:     127.0.0.1:58696 - "GET /openapi.json HTTP/1.1" 200 OK
INFO:     127.0.0.1:58893 - "GET /api/v1/healthcheck HTTP/1.1" 200 OK
WARNING:  StatReload detected changes in 'app.py'. Reloading...
INFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [56164]
INFO:     Started server process [63412]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

Databricks Apps runtime​

Assuming the code works locally, you can also deploy this application to a Databricks workspace using Databaricks Apps.

Follow the Get started with Databricks Apps for deployment instructions.

For the app configuration, use:

app.yaml
command: ["uvicorn", "app:app"]

The FastAPI and uvicorn packages are included in the default Databricks Apps environment.

For parity with your local code and to trigger Databricks Apps to install the latest package version, include a requirements.txt in your application folder as described in the following section.

Dependencies​

requirements.txt
fastapi
uvicorn