How to store global 'driver' variable (FastAPI Python)

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,
1

Hey I’m using Vercel right now to deploy my FastAPI app.

Locally, I was using the FastAPI lifespan to connect to the DB and manage sessions.

In main.py

from db import get_driver()

drivers = {}

@asynccontextmanager
async def lifespan(app: FastAPI):
    drivers["db"] = await get_driver()
    yield
    await drivers["db"].close()

In db.py

async def get_driver():
    return MyDB.driver(URI, auth)

async def get_session():
    from .main import drivers
    driver = drivers["db"]
    async with driver.session() as session:
        yield session

Elsewhere in my app I would then import the get_session() to perform operations. However, in Vercel I keep running into the issue KeyError drivers["db"] in the get_session() function as if the lifespan function isn’t called on startup and the drivers dictionary isn’t initialized properly :confused:

Am I doing something wrong or is this just a by-product of “serverless”? I’ve fixed the issue by creating a new driver & session at each request but I feel like this is not OK. Anybody got tips?

2

With serverless functions, you might have multiple instances and cannot save file changes to the server after deployment. That can cause problems like what you’re seeing. It can take a bit of adjustment to get a traditional server type of project working in a serverless environment.

There’s a Next.js FastAPI Starter that might help, though it doesn’t use exactly the same setup that you shared.

3

No DB connection is made or maintained on the FastAPI side of things in this template :confused:
So this is not really an answer to the question.

I saw in the other post you mentioned a project named Artha.ai. They split resources up between Vercel (for the frontend) and Render (for the FastAPI back-end). I’ll have to check to see if this is related to the serverless limitations

4

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