Python flask app on IIS not working on Windows Server 2019

Question

PROBLEM

I have simple flask application written in python that I would like to host using IIS on a Windows Server 2019 machine.

The app has already worked locally using the development server that comes with Flask. Furthermore the exact same code works perfectly on my window-server 2016 machine as well as my Windows7 workstation.

Frustratedly it thows an error 500 - "The FastCGI exited unexpectedly" when I try to run it under IIS on my Windows server 2019 machine. I have tried all sorts of things but have got nowhere. I hope that someone can help!

DESIGN

The app is an implementation of the wfastcgi approach described at this Microsoft webpage: https://learn.microsoft.com/en-us/visualstudio/python/configure-web-apps-for-iis-windows?view=vs-2019

The python script is

app_hello.py

from flask import Flask
app = Flask(__name__)

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

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

The web.config file is

web.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.webServer>
<handlers>
<add name="Python FastCGI" path="*" verb="*" modules="FastCgiModule" scriptProcessor="c:\devel\a_anomaly_detection\.venv\scripts\python.exe|c:\devel\a_anomaly_detection\.venv\lib\site-packages\wfastcgi.py" resourceType="Unspecified" requireAccess="Script" />
</handlers>
        <tracing>
            <traceFailedRequests>
                <add path="*">
                    <traceAreas>
                        <add provider="WWW Server" areas="Authentication,Security,Filter,StaticFile,CGI,Compression,Cache,RequestNotifications,Module,FastCGI,WebSocket" verbosity="Verbose" />
                    </traceAreas>
                    <failureDefinitions timeTaken="00:00:00" statusCodes="500" />
                </add>
            </traceFailedRequests>
        </tracing>
</system.webServer>
<appSettings>
<!-- Required settings -->
<add key="WSGI_HANDLER" value="app_hello.app" />
<add key="PYTHONPATH" value="c:\devel\a_anomaly_detection\website" />
<add key="WSGI_LOG" value="c:\devel\a_anomaly_detection\data\logs\wfastcgi.log" />
</appSettings>
</configuration>

My software versions are

• windows server 2019

• IIS 10

• python 3.7.6rc1

• wfastcgi 3.0.0

• Flask 1.1.2

error 500 page

[error_500_screen][1]

tracefailedRequests

I enabled tracefailedRequests and this is what was reported

51. NOTIFY_MODULE_START ModuleName="FastCgiModule", Notification="EXECUTE_REQUEST_HANDLER", fIsPostNotification="false" 09:08:17.333

52. FASTCGI_ASSIGN_PROCESS CommandLine="c:\devel\a_anomaly_detection.venv\scripts\python.exe c:\devel\a_anomaly_detection.venv\lib\site-packages\wfastcgi.py", IsNewProcess="true", ProcessId="3708", RequestNumber="1" 09:08:17.333

53. FASTCGI_START 09:08:17.333

54. FASTCGI_WAITING_FOR_RESPONSE 09:08:17.333

55. FASTCGI_UNEXPECTED_EXIT Error 09:08:17.349

56. SET_RESPONSE_ERROR_DESCRIPTION Warning ErrorDescription="c:\devel\a_anomaly_detection.venv\scripts\python.exe - The FastCGI process exited unexpectedly" 09:08:17.349

57. MODULE_SET_RESPONSE_ERROR_STATUS Warning ModuleName="FastCgiModule", Notification="EXECUTE_REQUEST_HANDLER", HttpStatus="500", HttpReason="Internal Server Error", HttpSubStatus="0", ErrorCode="The semaphore cannot be set again. (0x67)", ConfigExceptionInfo="" 09:08:17.349

58. NOTIFY_MODULE_END ModuleName="FastCgiModule", Notification="EXECUTE_REQUEST_HANDLER", fIsPostNotificationEvent="false", NotificationStatus="NOTIFICATION_FINISH_REQUEST" 09:08:17.349

Answer 1

Most likely you have forgotten to install on the server Python for your virtual environment. Have a look at c:\devel\a_anomaly_detection\.venv\pyvenv.cfg file and check if you indeed have Python in the folder, specified as a home parameter.

To troubleshoot, run from the c:\devel\a_anomaly_detection\website folder this command: c:\devel\a_anomaly_detection\.venv\scripts\python.exe c:\devel\a_anomaly_detection\.venv\lib\site-packages\wfastcgi.py and check its output

Answer 2

I know this is an old thread, but I just dealt with Internal Server 500 errors on a similar setup and hopefully these links will help others in the future.

I followed the guide here to get me started: https://medium.com/@dpralay07/deploy-a-python-flask-application-in-iis-server-and-run-on-machine-ip-address-ddb81df8edf3

I was still running into issues after trying to import other python modules (pandas / numpy), turns out I needed to add my PATH variable to my FastCGI settings (as mentioned by others here: numpy is already installed with Anaconda but I get an ImportError (DLL load failed: The specified module could not be found))