How to use FastAPI routers in azure app functions

Question

I'm trying to use FastAPI within my Azure App function. I've followed the MS tutorial and finally come up with the following files :

function_app.py

import azure.functions as func

from fastapi_app.main import app as fastapi_app

app = func.AsgiFunctionApp(app=fastapi_app, http_auth_level=func.AuthLevel.FUNCTION)

fastapi_app.main module

import azure.functions as func

import fastapi

from fastapi_app.api_v1.api import router as api_router

app = fastapi.FastAPI()

@app.get("/sample")
async def index():
    return {
        "info": "Try /hello/Shivani for parameterized route.",
    }


@app.get("/hello/{name}")
async def get_name(name: str):
    return {
        "name": name,
    }

app.include_router(api_router, prefix="/api/v1")

api_router module

from fastapi import APIRouter

from fastapi_app.api_v1.endpoints import users

router = APIRouter()
router.include_router(users.router, prefix="/users", tags=["Users"])

users module

from fastapi import APIRouter

router = APIRouter()


@router.get("/")
async def root():
    return {"message": "Get Users!"}

This is a very simple app. When I'm running my app locally (with func host start) I'm able to make the following request sucessfully wget http://localhost:7071/sample or wget http://localhost:7071/hello/myName and obtain the correct output.

When I'm going to http://localhost:7071/api/v1/users in my browser, I'm able to find the right output.

However, when I'm running wget http://localhost:7071/api/v1/users I have an error that tells me that the underlying connection has been closed. I have the same kind of issues when my Azure function is deployed in Azure.

Because of that I'm guessing it should be an issue regarding the usage of FastAPI Router but I was unable to find anything that make it work.

Any help appreciated !

Answer 1

Hello BERGES Armand,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

I understand that you would like to know how you can use FastAPI routers in azure app functions.

The error (The underlying connection has been closed) suggests there may be a timeout or connection problem. So, you can try to set longer timeouts in your request or debugging this using Azure's logs and try to review the following settings and configurations:

1. Check your function.json configuration is correct for the Azure Functions environment. If you don't have it already, you need to create a function.json file.
2. If you use external tools like wget, you might run into CORS issues, so you have to add CORS middleware to your FastAPI app like the below:

from fastapi.middleware.cors import CORSMiddleware
app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],  # Adjust as necessary for security
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

3. Set your app to always be warm, it might be a cold start issue.
4. Your routes are working fine for /sample and /hello/{name}, but you’re having trouble with /api/v1/users. Double-check that your FastAPI router setup is correct:

In api_router:

router.include_router(users.router, prefix="/users", tags=["Users"])

5. After making these changes locally, redeploy your app to Azure Functions, and enable "Always On" if you're experiencing cold start issues on Azure.

I hope this is helpful! Do not hesitate to let me know if you have any other questions.

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Answer 2

Hello @BERGES Armand

One thing to check is whether you have properly defined the users router in your api_router module. In your users module, you have defined a root endpoint with @router.get("/"), but you have not defined an endpoint for /api/v1/users.

You should define an endpoint for /api/v1/users in your users module like this:

@router.get("/api/v1/users") async def get_users(): 
return {"message": "Get Users!"}

Then, in your api_router module, you can include the users router with the prefix /api/v1/users like this:

from fastapi import APIRouter
from fastapi_app.api_v1.endpoints import users
router = APIRouter() 
router.include_router(users.router, prefix="/api/v1/users", tags=["Users"])

With these changes, you should be able to access the /api/v1/users endpoint of your FastAPI app when running your Azure Function.

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