Error 500 while running a Python Flask application on IIS. How to get the actual error

I try to get a Flask application running on an IIS on windows.

The reason is to get single-sign-on with windows authentication done using the IIS mechanisms.

I got it running on my development machine. But it doesn't work in the actual production environment. I get a error 500 for some reasons, but I don't see the actual Flask error message.

I saw the python error message ones during the setup, before I set the rights to write to the log file. It told me about the missing rights. That should mean FastCGI is configured the right way, I guess.

Now after I set the write access, I get a IIS error 500 page that tells me that something went wrong with the FastCGI. But I don't get any log entry, even if I set the rights to write them. No log files and no entries in the windows event logs. Nothing.

Do you know a way to get the actual error message?

[Update] After enabling the failed request trace, I get the following error:

<RenderingInfo Culture="en-US">
  <Opcode>FASTCGI_UNKNOWN_ERROR</Opcode>
  <Keywords>
   <Keyword>FastCGI</Keyword>
  </Keywords>
  <freb:Description Data="ErrorCode">The directory name is invalid.
(0x8007010b)</freb:Description>
</RenderingInfo>

The web.config looks like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <appSettings>
    <add key="PYTHONPATH" value="C:\inetpub\wwwroot\app_name" />
    <!-- The handler here is specific to Bottle; see the next section. -->
    <add key="WSGI_HANDLER" value="main.app" />
    <add key="WSGI_LOG" value="C:\inetpub\wwwroot\app_name\LogFiles\wfastcgi.log" />
  </appSettings>
  <system.web>
            <customErrors mode="Off" />
  </system.web>
  <system.webServer>
    <handlers>
      <clear />
      <add name="Python FastCGI" path="*" verb="*" modules="FastCgiModule" 
                          scriptProcessor="&quot;c:\program files\python37\python.exe&quot;|&quot;c:\program files\python37\lib\site-packages\wfastcgi.py&quot;" 
                          resourceType="Unspecified" requireAccess="Script" />
    </handlers>
    <security>
      <authentication>
        <anonymousAuthentication enabled="false" />                       
                        <windowsAuthentication enabled="true" />
      </authentication>
    </security>
  </system.webServer>
</configuration>

If I would guess, the path to the "program files" folder with the blank inside would cause the error.

To configure python flask app in iis you could follow the below steps:

• First, you need to install the python,wfastcgi, and flask at your server.
• You can download the python from below link:

https://www.python.org/downloads/

note: if possible please use python version above 3.6.

after installing python install the wfastcgi.run the command prompt as administrator and run below command:

pip install wfastcgi

wfastcgi-enable

below is my flask example:

from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
    return "Hello from FastCGI via IIS!"
if __name__ == "__main__":
    app.run()

after creating an application to run it use below command:

python app.py

now enable the cgi feature of iis:

• now open iis.
• right-click on the server name and select add site.

• enter the site name physical path and the site binding.
• after adding site select the site name and select the handler mapping feature from the middle pane.

• Click “Add Module Mapping”

executable path value:

C:\Python37-32\python.exe|C:\Python37-32\Lib\site-packages\wfastcgi.py

• Click “Request Restrictions”. Make sure “Invoke handler only if the request is mapped to:” checkbox is unchecked:

• Click “Yes” here:

• now go back and select the application setting feature.

• click add from the action pane.

• Set the PYTHONPATH variable(which is your site folder path):

• And the WSGI_HANDLER (my Flask app is named app.py so the value is app.app — if yours is named site.py it would be site.app or similar):

• Click OK and browse to your site.