Flask mounted with WSGIMiddleware gets request context mixed

[conradogarciaberrotaran]

Description

Hi everyone, i'm starting to migrate from Flask to FastAPI. I thought of doing this by mounting the old flask app under a new FastAPI instance like this:

app = create_fastapi_app()

flask_app = create_flask_app()

app.mount("/", WSGIMiddleware(flask_app))

My flask app uses the before_request hook to set the current user.

def set_authenticated_user():
    current_app.authenticated_user = None
    if "authorization" in request.headers:
        current_app.authenticated_user = (
            AuthenticatedUserRequest.get_authenticated_user()
        )


def create_flask_app():
    app = Flask(__name__)
    ...
    app.before_request(set_authenticated_user)

My flask app also has a healthcheck endpoint as a kubernetes liveness probe. This request does not contain the authorization header.
My problem is this:
Whenever I have the liveness probe turned on (requests are hitting the healthcheck endpoint), sometimes I get an empty authenticated user in the current_app.
After debugging a lot, im seeing that the before_request is getting called and the authenticated user is being set correctly. But in the actual request, is not set. This happens a lot when liveness probe.
This problem dissapears whenever I only deploy the flask app by its own and this problem happens much less whenever I disable the liveness probe.
My theory is that when the app is mounted, the "request contexts" are being mixed up. Meaning, that the current_app for one request is being handled for another request.
Is this posible?
Im deploying with gunicorn and Uvicorn worker

Thanks

Environment

• OS: Linux
• FastAPI Version: 0.63.0
• Python-version: 3.7

[tiangolo]

I would actually try to deploy the Flask app independently and handle routing based on path prefix with a Proxy like Traefik, probably also doing the HTTPS part.

Flask's internals are a bit finicky, even more, if you are are heavily using Flask's own psedo-global objects. There might be a way to solve it, but it probably depends a lot on your code, and would probably take a lot of effort debugging it, so, if you can avoid it, that might be easier.

But anyway, if you still have problems, please add a self-contained, minimal, reproducible, example that I can copy-paste to replicate it.

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.

[github-actions[bot]]

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