Including WSGI - Flask, Django, others

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You can mount WSGI applications as you saw with Sub Applications - Mounts, Behind a Proxy.

For that, you can use the WSGIMiddleware and use it to wrap your WSGI application, for example, Flask, Django, etc.

Using WSGIMiddleware

Info

This requires installing a2wsgi for example with pip install a2wsgi.

You need to import WSGIMiddleware from a2wsgi.

Then wrap the WSGI (e.g. Flask) app with the middleware.

And then mount that under a path.

Python 3.9+

from a2wsgi import WSGIMiddleware
from fastapi import FastAPI
from flask import Flask, request
from markupsafe import escape

flask_app = Flask(__name__)


@flask_app.route("/")
def flask_main():
    name = request.args.get("name", "World")
    return f"Hello, {escape(name)} from Flask!"


app = FastAPI()


@app.get("/v2")
def read_main():
    return {"message": "Hello World"}


app.mount("/v1", WSGIMiddleware(flask_app))

Note

Previously, it was recommended to use WSGIMiddleware from fastapi.middleware.wsgi, but it is now deprecated.

It’s advised to use the a2wsgi package instead. The usage remains the same.

Just ensure that you have the a2wsgi package installed and import WSGIMiddleware correctly from a2wsgi.

Check it

Now, every request under the path /v1/ will be handled by the Flask application.

And the rest will be handled by FastAPI.

If you run it and go to http://localhost:8000/v1/ you will see the response from Flask:

Hello, World from Flask!

And if you go to http://localhost:8000/v2 you will see the response from FastAPI:

{
    "message": "Hello World"
}