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Random HTTP 500 errors Session not found errors
#1
Hi
 
I am using Intraweb 14.2.8 and one of our clients are having issues with our application. They are getting "This page can't be displayed" at random times when performing an update or action in the Intraweb Application. This error message appears randomly and does not affect all users. the frequency varies during use of the application. Sometime when clicking Fix connection problems, the application page reappears again and if that is not successful they have to restart the application with a new session. The error message "this page can't be displayed" is a friendly message that appears seems to be the default display from IE for HTTP errors greater than 400. Upon inspecting the HTTP traffic, we found many HTTP 500 errors with session not found that correlates with the user reported error timings.
 
A couple of questions I had are:
 1. what would cause these errors apart from a session timeout?
 2. what parameters in IIS or Intraweb could affect this
 3. if this is caused by an application exception, can these be logged into a log file by enabling the ExceptionLogger property in the ServerController and get information such as the stack trace 
 4. can user sessions be logged into a log file?
 
 
Info on the Application:
1. Uses Intraweb 14.2.8
2. Running on IIS 8.5 Windows 2012 Server
3. Multiple websites accessing the same physical dll
4. This particular client has the highest number of users and furthest away from the Web Server
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#2
To me it sounds like some user code is crashing and causing the sessions to fail. 500 are unknown errors, ie user code in 99% of the times. I would suggest turning on the debug options in server controller and logging more to narrow it down.
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#3
(01-03-2019, 05:09 AM)jbkar2 Wrote: Hi
 
I am using Intraweb 14.2.8 and one of our clients are having issues with our application. They are getting "This page can't be displayed" at random times when performing an update or action in the Intraweb Application. This error message appears randomly and does not affect all users. the frequency varies during use of the application. Sometime when clicking Fix connection problems, the application page reappears again and if that is not successful they have to restart the application with a new session. The error message "this page can't be displayed" is a friendly message that appears seems to be the default display from IE for HTTP errors greater than 400. Upon inspecting the HTTP traffic, we found many HTTP 500 errors with session not found that correlates with the user reported error timings.
 
A couple of questions I had are:
 1. what would cause these errors apart from a session timeout?
 2. what parameters in IIS or Intraweb could affect this
 3. if this is caused by an application exception, can these be logged into a log file by enabling the ExceptionLogger property in the ServerController and get information such as the stack trace 
 4. can user sessions be logged into a log file?
 
 
Info on the Application:
1. Uses Intraweb 14.2.8
2. Running on IIS 8.5 Windows 2012 Server
3. Multiple websites accessing the same physical dll
4. This particular client has the highest number of users and furthest away from the Web Server

First thing, you should enable your IIS to display error messages (status code 500) coming from your application. Here is how (item 6):

http://docs.atozed.com/docs.dll/deployme...20IIS.html

1- Session not found means that the cookie session contains a value which doesn't correspond to any session in the server. Hard to say why it happens without more information

2- If your application pool is recycling for instance, all sessions will be reset. In that case all active users will notice the same thing, not only one or a few

3- Here is how to use the exception logger to help you to find exceptions:

http://docs.atozed.com/docs.dll/developm...ogger.html

You *must* turn on stack trace support using IWJcl units provided with IntraWeb

4- ServerController.LogSessionEvents = True will log all session requests to a file which can be inspected using an external IW tool. Read more about it here: https://www.atozed.com/2014/01/20140604a-en/

Please notice that session logging has a performance penalty and shouldn't be used in production, unless when investigating some problem like this.
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#4
Thank you for your input. It is much appreciated. I enabled logging in the Server controller and the Exception that we are getting is

Exception message  : Session ID is invalid.
Exception class        : EInvalidAppID

I know this error usually happens when a session has expired. However, I suspect this is not the case here as there are way too many session ID Invalid error messages in a short time frame in respect to the number of users.

I suspect the application session ids are being dropped or being lost somehow but I am not sure what would be causing it. Some question I have though.
1.Can Server bandwidth or other Server constraints (ISAPI requests/counts) affect the performance of the application such as sessions being dropped or slow performance?
2. Can the error message "session is invalid" be caused by the load balancer not redirecting the request to the Server(where the session was established) which the first request originated from? (ie there is no active session on the other application servers). There are multiple application servers on which the application is being run on. The load balancer directs traffic to a certain application server in which a session is established and subsequent requests should be redirected to the Server where the session was established.
A couple of questions on scaling up and performance tuning
1. what is the maximum number of client connections or sessions can Intraweb Handle?
2. Can the application handle high volumes of users on a single IIS Server with a single application pool and Website?
3. Is it recommended to have multiple application pools and Websites on the single IIS Server ?(ie to distribute traffic on different ports within the same application server)
4. are there any IIS configurations that can better the performance for the Intraweb Application
5. is there any documentation or recommendation when scaling up or performance tuning the Intraweb Application?
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