python - Azure Flask HTTP Error 500.0 - INTERNAL SERVER ERROR

Question

I have a simple flask web app hosted on Microsoft Azure which allows users to login, upload files, view uploaded files and logout.
Now to handle users more efficiently I decided to use session from flask.
here is my sample code

'''import statements'''
from flask import render_template, request, session
'''more import statements'''

@app.route('/')
def home():
    return render_template('login.html')

@app.route('/login_user', methods=['GET', 'POST'])
def login_user():
    username = str(request.form['username'])
    password = request.form['password']
    connection = MongoClient('mongodb://username:[email protected]:pot_number/db_name')
    collection = connection.db_name.demo

    record = collection.find_one({'username':username})
    if password == record['password']:
        session['username'] = username
        return render_template('index.html')
    else:
        login_message = "Invalid Username/Password"
        return render_template('login.html',login_message=login_message)

@app.route('/upload', methods=['GET', 'POST'])
def upload():
    if 'username' in session:
        return render_template('upload.html')
    else:
        return render_template('login.html')

@app.route('/logout', methods=['GET', 'POST'])
def logout():
    session.pop('username',None)
    return render_template('login.html')

whenever i try to add session['username'] = username the app crashes giving a Internal server error.

Im not sure what log file to post since I am new to Azure. Here is the event log

Application ID: /LM/W3SVC/1909144379/ROOT

Process ID: 69820

Exception: System.Configuration.ConfigurationErrorsException

Message: Couldn't find type for class Microsoft.WindowsAzure.Diagnostics.DiagnosticMonitorTraceListener, Microsoft.WindowsAzure.Diagnostics, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35.

StackTrace:    at System.Diagnostics.TraceUtils.GetRuntimeObject(String className, Type baseType, String initializeData)
   at System.Diagnostics.TypedElement.BaseGetRuntimeObject()
   at System.Diagnostics.ListenerElement.GetRuntimeObject()
   at System.Diagnostics.ListenerElementsCollection.GetRuntimeObject()
   at System.Diagnostics.TraceInternal.get_Listeners()
   at System.Diagnostics.TraceInternal.WriteLine(String message)
   at System.Diagnostics.Debug.WriteLine(String message)
   at Microsoft.Web.Compilation.Snapshots.SnapshotHelper.TakeSnapshotTimerCallback(Object stateInfo)
   at System.Threading.TimerQueueTimer.CallCallbackInContext(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.TimerQueueTimer.CallCallback()
   at System.Threading.TimerQueueTimer.Fire()
   at System.Threading.TimerQueue.FireNextTimers()
   at System.Threading.TimerQueue.AppDomainTimerCallback()</Data></EventData></Event><Event><System><Provider Name=".NET Runtime"/><EventID>1026</EventID><Level>0</Level><Task>0</Task><Keywords>Keywords</Keywords><TimeCreated SystemTime="2016-07-05T10:03:46Z"/><EventRecordID>348982031</EventRecordID><Channel>Application</Channel><Computer>RD00155DFA5791</Computer><Security/></System><EventData><Data>Application: w3wp.exe
Framework Version: v4.0.30319
Description: The process was terminated due to an unhandled exception.
Exception Info: System.Configuration.ConfigurationErrorsException
   at System.Diagnostics.TraceUtils.GetRuntimeObject(System.String, System.Type, System.String)
   at System.Diagnostics.TypedElement.BaseGetRuntimeObject()
   at System.Diagnostics.ListenerElement.GetRuntimeObject()
   at System.Diagnostics.ListenerElementsCollection.GetRuntimeObject()
   at System.Diagnostics.TraceInternal.get_Listeners()
   at System.Diagnostics.TraceInternal.WriteLine(System.String)
   at System.Diagnostics.Debug.WriteLine(System.String)
   at Microsoft.Web.Compilation.Snapshots.SnapshotHelper.TakeSnapshotTimerCallback(System.Object)
   at System.Threading.TimerQueueTimer.CallCallbackInContext(System.Object)
   at System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
   at System.Threading.TimerQueueTimer.CallCallback()
   at System.Threading.TimerQueueTimer.Fire()
   at System.Threading.TimerQueue.FireNextTimers()
   at System.Threading.TimerQueue.AppDomainTimerCallback()

</Data></EventData></Event></Events>

here is the stack trace

2016-07-05T09:48:45
System.ApplicationException: The trace listener AzureBlobTraceListener is disabled. ---> System.InvalidOperationException: The SAS URL for the cloud storage account is not specified. Use the environment variable 'DIAGNOSTICS_AZUREBLOBCONTAINERSASURL' to define it. at Microsoft.WindowsAzure.WebSites.Diagnostics.AzureBlobTraceListener.RefreshConfig()
--- End of inner exception stack trace ---

Here is the Detailed error

Detailed Error Information:
Module     FastCgiModule
Notification       ExecuteRequestHandler
Handler    Python FastCGI
Error Code     0x00000000
Requested URL      http://SuperFlask:80/handler.fcgi/login_user
Physical Path      D:homesitewwwroothandler.fcgilogin_user
Logon Method       Anonymous
Logon User     Anonymous

Answer 1

Have you set app.secret_key before using session variable? I had same issue, it worked locally, but threw 'Internal Server Error' in azure, because I set it in if _name__ == '_main__' block like this:

if __name__ == '__main__':
  HOST = environ.get('SERVER_HOST', 'localhost')
  try:
      PORT = int(environ.get('SERVER_PORT', '5555'))
  except ValueError:
      PORT = 5555
  app.secret_key = "secret_key"    
  app.run(HOST, port=PORT)

I set app.secret_key = "secret_key" outside of the if block and it worked.