Deploying FastAPI to Vercel

Introduction

I usually only deploy Next.js apps to Vercel and haven't really looked into the other runtimes that they offer for running serverless functions. In this article we will deploy a FastAPI app to Vercel, using the Python serverless runtime.

Set up FastAPI app

We set up the FastAPI app as follows:

mkdir fastapi-vercel
cd fastapi-vercel

# Create virtual environment
python3 -m venv venv
source venv/bin/activate

# Install FastAPI
pip install fastapi uvicorn

We now create our api.py file in the server directory:

# server/api.py
from fastapi import FastAPI
from .routes import router as NoteRouter

app = FastAPI()


@app.get("/", tags=["Deploy FastAPI to Vercel"])
async def root() -> dict:
    return {"message": "Hello world"}

Now we create main.py as our app root:

# main.py
import uvicorn

if __name__ == "__main__":
    uvicorn.run("server.api:app", host="0.0.0.0", port=8000, reload=True)

Now to run the dev server just run:

python3 main.py

Navigate to http://localhost:8000/docs to see your beautiful OpenAPI docs page.

Deploying to Vercel

Firstly ensure you have the Vercel CLI installed:

npm i -g vercel

We first need a vercel.json file in the root directory to handle to config:

{
  "builds": [{ "src": "/server/api.py", "use": "@vercel/python" }],
  "routes": [{ "src": "/(.*)", "dest": "server/api.py" }]
}

We can now deploy to Vercel:

vercel .

The first time you will need to authenticate with Vercel, and if you wish you can link a Github repository to have builds run on each push.