Not able to serve Python Flask app from IIS Web Application

Question

I am trying to serve Flask app from IIS Web Application under Default Web Site, but am not able to get it working. Here are the details:

OS: Windows Server 2016 DataCenter Edition
IIS: Installed with all options including CGI
IIS Rewrite Module: Version 2 installed

Steps I've taken:

1. Install IIS with all components (with CGI)
2. Install Python 2.7.14
3. Add Python in the PATH variable
4. pip install wfastcgi
5. wfastcgi-enable
6. pip install flask
7. iisreset
8. Create Directory: C:\inetpub\wwwroot\flask-demo
9. Click Convert to Application in IIS for above directory.
10. Create C:\inetpub\wwwroot\flask-demo\myapp.py with following content:

from flask import Flask
app = Flask(__name__)

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

if __name__ == "__main__":
    app.run()

11. Create C:\inetpub\wwwroot\flask-demo\web.config with following content:

<configuration>
  <system.webServer>
    <handlers>
      <remove name="Python FastCGI" />
      <add name="Python FastCGI"
           path="*"
           verb="*"
           modules="FastCgiModule"
           scriptProcessor="C:\Python27\python.exe|C:\Python27\Lib\site-packages\wfastcgi.pyc"
           resourceType="Unspecified"
           requireAccess="Script" />
    </handlers>
   <rewrite>
 <rules>
 <rule name="asset-url-rewrite" stopProcessing="true">
 <match url="static" />
 <conditions>
 </conditions>
 <action type="Rewrite" url="flask-demo/{R:0}" />
 </rule>
 <rule name="app-url-rewrite" stopProcessing="true">
 <match url="[a-zA-Z]+" />
 <conditions>
 </conditions>
 <action type="Rewrite" url="flask-demo/" />
 </rule>
 </rules>
 </rewrite>
  </system.webServer>
  <appSettings>
    <add key="WSGI_HANDLER" value="myapp.app" />
    <add key="PYTHONPATH" value="C:\inetpub\wwwroot\flask-demo" />
  </appSettings>
</configuration>

Problem

When I try to access page as http://localhost/flask-demo, am getting 404. But if I change 2nd line in myapp.py from @app.route('/') to @app.route('/flask-demo') where flask-demo is the name of the IIS web application where Python files are placed, it works.

I wish to serve Python web page without writing flask-demo / name of IIS web application where Python flask app is placed. Am not able to do that.

I tried to use app.config['APPLICATION_ROOT'] = '/flask-demo', but it didn't worked.

What is the best way to get this working? Followed article https://medium.com/@bilalbayasut/deploying-python-web-app-flask-in-windows-server-iis-using-fastcgi-6c1873ae0ad8 but it didn't helped.

Answer 1

The URL includes flask-demo so it is normal that Flask see it, and it use it.

There are some workarounds, e.g.:

Add a prefix to all Flask routes (on this site).

In general: what to you want? The URL is much more important than the underling technology (and URL should be stable, also when you change implementation). I recomment not to have flask-demo in the URL (and NEVER something with test and demo, anyway, demo are made to remain forever, unfortunately). So I would modify ISS so that it will redirect all dynamic pages to flask-demo.

Answer 2

After multiple tries, I've reached out to following solution.

Solution Caveat

This assumes that Python application is hosted only at first depth level of IIS website. Solution below does not support 2nd level dept.

New myapp.py

from flask import Flask
import os
app = Flask(__name__)

ROOT_PREFIX = '/' + os.path.dirname(os.path.realpath(__file__)).rsplit('\\', 1)[-1]

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

if __name__ == "__main__":
    app.run()

New web.config

<configuration>
    <system.webServer>
        <modules>
            <remove name="WebDAVModule" />
        </modules>
        <handlers>
            <remove name="WebDAV" />
            <add name="Python FastCGI"
                        path="*"
                        verb="*"
                        modules="FastCgiModule"
                        scriptProcessor="C:\Python27\python.exe|C:\Python27\Lib\site-packages\wfastcgi.pyc"
                        resourceType="Unspecified"
                        requireAccess="Script" />
        </handlers>
    </system.webServer>
    <appSettings>
        <add key="WSGI_HANDLER" value="myapp.app" />
        <add key="PYTHONPATH" value="C:\inetpub\wwwroot\flask-demo" />
    </appSettings>
</configuration>