Azure use python flask framework for function app

Question

I saw that Azure now supports Python (preview) in the function apps. I have a existing Flask app and was wondering if it\'s possible to deploy that one as a function app without

Answer 1

I tried different ways to integrate Azure Functions for Python with Flask framework. Finally, I did it success in my HttpTrigger function named TryFlask via app.test_client().

Here is my sample code, as below.

import logging
import azure.functions as func
from flask import Flask, request

app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

@app.route('/hi')
def hi():
    return 'Hi World!'

@app.route('/hello')
@app.route('/hello/<name>', methods=['POST', 'GET'])
def hello(name=None):
    return name != None and 'Hello, '+name or 'Hello, '+request.args.get('name')

def main(req: func.HttpRequest) -> func.HttpResponse:
    logging.info('Python HTTP trigger function processed a request.')
    uri=req.params['uri']
    with app.test_client() as c:
        doAction = {
            "GET": c.get(uri).data,
            "POST": c.post(uri).data
        }
        resp = doAction.get(req.method).decode()
        return func.HttpResponse(resp, mimetype='text/html')

For testing on local and Azure, to access the urls /, '/hi' and /hello via the url http(s)://<localhost:7071 or azurefunchost>/api/TryFlask with query string ?uri=/, ?uri=/hi and ?uri=/hello/peter-pan in browser, and to do the POST method for the same url above with query string ?uri=/hello/peter-pan, these are all work. Please see the results as the figures locally below, the same on cloud.

Note: In my solution, the url must have to be http(s)://<localhost:7071 or azurefunchost>/<routePrefix defined in host.json, default is api>/<function name>?uri=<uri defined in app.route, like / or /hi or /hello, even /hello/peter-pan?name=peter>.

Answer 2

Flask can be used now out of the box with Python Azure Functions -> see https://github.com/Azure/azure-functions-python-library/pull/45

Answer 3

Flask app is just an WSGI application. WSGI is a rather simple interface (see http://ivory.idyll.org/articles/wsgi-intro/what-is-wsgi.html. So instead of using test_client() as middleware to connect to the Azure function environment, a proper wsgi wrapper implementation should be used, which calls the app=Flask() object.

There is a nice Azure Python wsgi wrapper implementation "azf-wsgi" available in https://github.com/vtbassmatt/azf-wsgi.

In order to use the azf-wsgi wrapper with Flask, I found it useful to use a middleware to rewrite the URL:s from /api/app to / so when developing, I don't need to know where my Flask app gets mounted. Additional benefit is that my main.py is just a normal Flask application, which I can run locally without using Azure functions environment (way faster).

My HttpTriggerApp/__init__.py of Azure function is attached. The myFlaskApp-folder is located under the HttpTriggerApp. Remember to use rlative import in the http-trigger as well as main.py (from . import myHelperFooBar).

For host.json and function.json, follow the azf-wsgi instructions.

import logging
import azure.functions as func

# note that the package is "azf-wsgi" but the import is "azf_wsgi"
from azf_wsgi import AzureFunctionsWsgi

# Import the Flask wsgi app (note relative import from the folder under the httpTrigger-folder.
from .myFlaskAppFolder.main import app

# rewrite URL:s to Azure function mount point (you can configure this in host.json and function.json)
from werkzeug.middleware.dispatcher import DispatcherMiddleware
app.config["APPLICATION_ROOT"] = "/api/app"     # Flask app configuration so it knows correct endpoint urls
application = DispatcherMiddleware(None, {
    '/api/app': app,
})

# Wrap the Flask app as WSGI application
def main(req: func.HttpRequest, context: func.Context) -> func.HttpResponse:
    return AzureFunctionsWsgi(application).main(req, context)