Python/Flask Login form throws 500 error on IIS

Question

Due to my restrictions at work, I have to rely on hosting my webapp on IIS 7.5 . I configured IIS to serve the application via wfastcgi.py .

The issue is, that a login form, throws an HTTP 500 error on IIS, when clicking on the login button. The site gets loaded without issue. Also, code works perfectly fine, when I am running it on the flask development server.

I have an extended version of the code, with access to a sqlite DB. I was able to narrow down the issue to the login session creation part. I am not sure, whether the issue is about the way how IIS handles POST and GET requests with wfastcgi.py , or something else.

Here's the simplified version of the code, which throws the same error: UPDATE : Changed the view functions to the proper return redirect.

import wiw_ad_controller as parser
import sys
from flask import Flask, flash, render_template, redirect, url_for, request, session, abort
import os



app = Flask(__name__)

@app.route('/')
@app.route('/index', methods=['GET', 'POST'])
def index():
    if not session.get('logged_in'):

        return render_template('login.html')        
    else:
        return render_template('index.html')        


@app.route('/login', methods=['POST'])
def login():
    if request.form['username'] == 'admin' and request.form['password'] == 'admin':
        session['logged_in'] = True
        flash("Login was successfull")
    else:
        flash("Wrong password!")
    return redirect(url_for('index')) 


@app.route('/search', methods=['GET','POST'])
def lookup_data():
    if (session.get('logged_in')==True):
        if request.method == 'POST' or request.method == 'GET':

            if (request.form['gpn'] and request.form['gpn'].isdigit()):

                #code removed - not needed
                return render_template('fetched_data.html', user_wiw=user_wiw, user_ad=user_ad)
            else:
                flash('Wrong ID')
            return index()
    return redirect(url_for('index')) 


@app.route("/logout")   
def logout():
    session['logged_in'] = False
    return redirect(url_for('index')) 


@app.errorhandler(500)
def internal_error(exception):
    app.logger.exception(exception)
    return render_template('500.html'), 500 


@app.errorhandler(404)
def internal_error(exception):
    app.logger.exception(exception)
    return render_template('404.html'), 404




if __name__ == '__main__':
    app.secret_key=os.urandom(12)
    app.run(debug=True)

Answer 1

Found out the issue. I didn't realize, that by calling my script via wfastcgi.py , the main function never runs.

The login feature did not work, because it needed app.secret_key=os.urandom(12) to be run first.

I used the following code by Miguel Grinberg to find out what the issue is, since debug=True did not provide any output in a IIS prod environment.

@app.errorhandler(500)
def internal_error(exception):
    app.logger.exception(exception)
    file_handler = RotatingFileHandler('C:\inetpub\wwwroot\logs.log', 'a', 1 * 1024 * 1024, 10)
    file_handler.setFormatter(logging.Formatter('%(asctime)s %(levelname)s: %(message)s [in %(pathname)s:%(lineno)d]'))
    app.logger.setLevel(logging.INFO)
    file_handler.setLevel(logging.INFO)
    app.logger.addHandler(file_handler)
    app.logger.info('microblog startup')
    return render_template('500.html'), 500 

Hope, this will help others in the same situation as me.

Note: Read/Write permissions have to be set on wwwroot and all files in order for this to work.

You also need to import logging, from logging import RotatingFileHandler, import render_template from flask, create 500.html file in tempaltes folder.

Answer 2

The return of your view functions ( search() and login() ) is incorrect. Eg

return redirect(url_for('index'))

should be used for returning to the index page.

See the Flask documentation on redirects.

Answer 3

I had this same error but my app already had a secret key.

Alas! after two days of searching I used your function to display the traceback and I narrowed down to my problem.

The process executing the app did not have access to the database. This problem is related to configuration of iis. The identity of the application pool has to have access to the DB. U can change this identity as instructed here

For other problems anyone faces in iis using Flask I would recommend googling them with using the name asp.net not python or flask eg: Use : "IIS internal server error asp.net" Instead of : "IIS internal server error flask"

Answer 4

Guys I had the same problem. Here is the solution which works for most people. This issue happens because the server connects to the database without the secret_key or something.

Make sure you put the following line right under your declaration of the Flask app (In the example app = Flask())

app.secret_key=os.urandom(12)
app.run(debug=True)

With the above you will easily be able to debug the issue.