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One reason for getting a ‘No HTTP triggers found’ error when using Azure Functions with Python V2 programming model

Summary: It might be because there is an exception raised when importing your function_app.py – for example, caused by one of your import statements raising an exception, or a parsing error caused by a syntax error.

I was deploying a FastAPI app to Azure Functions recently. Azure Functions is the equivalent of AWS Lambda – it provides a way to run serverless functions.

Since I’d last used Azure Functions, Microsoft have introduced the Azure Functions Python V2 programming model which makes it easier and cleaner to do a number of common tasks, such as hooking up a FastAPI app to run on Functions.

However, it also led to an error that I hadn’t seen before, and that I couldn’t find documented very well online.

Specifically, I was getting an error at the end of my function deployment saying No HTTP triggers found. I was confused by this because I had followed the documented pattern for setting up a FastAPI app. For reference, my function_app.py file looked a bit like this:

import azure.functions as func
from complex_fastapi_app import app

app = func.AsgiFunctionApp(app=app,
            http_auth_level=func.AuthLevel.ANONYMOUS) 

This was exactly as documented. But I kept getting this error – why?

I replaced the import of my complex_fastapi_app with a basic FastAPI app defined in function_app.py, this time copied directly from the documentation:

import azure.functions as func 
from fastapi import FastAPI, Request, Response 

fast_app = FastAPI()

@fast_app.get("/return_http_no_body") 
async def return_http_no_body(): 
    return Response(content="", media_type="text/plain") 

app = func.AsgiFunctionApp(app=fast_app, 
                           http_auth_level=func.AuthLevel.ANONYMOUS) 

Everything worked fine now and I didn’t get the error.

After a lot of debugging, it turns out that if there is an exception raised when importing your function_app.py file then Functions won’t be able to establish what HTTP triggers you have, and will give this error.

In this case, I was getting an exception raised when I imported my complex_fastapi_app, and that stopped the whole file being processed. Unfortunately I couldn’t find anywhere that this error was actually being reported to me – I must admit that I find Azure logging/error reporting systems very opaque. I assume it would have been reported somewhere – if anyone reading this can point me to the right place then that’d be great!

I’m sure there are many other reasons that this error can occur, but this was one that I hadn’t found documented online – so hopefully this can be useful to someone.

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This post originally appeared on Robin's Blog.

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Categorised as: Computing, How To, Programming, Python