I need to use an HTTP client in my Azure Function. I can use aiohttp like this (this is a minimalistic example form the MSFT documentation).

import aiohttp

import azure.functions as func

async def main(req: func.HttpRequest) -> func.HttpResponse:
    async with aiohttp.ClientSession() as client:
        async with client.get("URL") as response:
            return func.HttpResponse(await response.text())

    return func.HttpResponse(body='NotFound', status_code=404)

However, this creates a new session object for each request, which should be avoided, as per the aiohttp documentation, as it’s an expensive operation.

My question is – how can I instantiate a session object once and share it between function calls? From the ClientSession code, it looks like __aenter__ doesn’t do anything, so I could instantiate the session just by calling session = aiohttp.ClientSession(). However, where would I call __aexit__?

Or is there even a better way to instantiate and clean up global objects in Azure Functions that require async instantiation and clean-up?