XenApp 6.5 Session starts then disappears

We started experiencing issues where a user would launch their XenApp 6.5 session, but the application never showed on screen.  When watching in the AppCenter (using quick refreshes) you can see the application start, drop into a disconnected state, and then logoff.


After some very fast Google searches and looking at Citrix forums there is a lot of information on this.  Unfortunately, I found that none of them hit on the root cause in my environment.


Possible causes found from various posts and Citrix KB articles:


Possible caused by VMware EVC - not in my case

• http://support.citrix.com/article/CTX131628
• http://danielruiz.org/2012/08/17/xenapp-version-6-5-session-launch-issues-with-vmware-evc/

In my case EVC was turned on, but it had always been turned on and I haven't seen this issue before or rather it had been extremely rare and usually resolved by rebooting a XenApp server in error.  So why would EVC suddenly cause me an issue when we've been running for a year with no issue?


Possible caused by Citrix EUEM (Edgesight)

• http://support.citrix.com/article/CTX139150

Not in my environment.  At one time I attempted to use Edgesight, but quickly found that the C++ libraries conflicted with our main application.  It's been disabled since and I haven't gotten back around to turning it on since the fix was released.


Default 1 minute time-out exceeded for long logons

• http://support.citrix.com/article/CTX138404

This one doesn't actually really hit on a cause imo, rather the effect.  The effect here is that logons are taking a long time and so it hits the timeout.  The cause is unknown, that's where we need to dig in and find out why in order to make logins more timely.  Just increasing the "timeout" while helpful in the short term doesn't fix the root cause.


The root issue in my case
After having looked at all the above my partner in crime says to me "AD users and computers seems slower to load lately".  That's strange.


After a quick look at all the Domain Controllers in the environment the issue becomes very obvious.  The DC's CPU's are pegged out, as is their RAM...  We can all do the math there, run out of RAM and it's going to start paging and burn up CPU.


After a quick addition of RAM (and added an additional CPU for kicks) all is wonderful again.  XenApp launches significantly faster and the timeout is no longer reached causing the timeout.




Don't just increase the timeout!  See if there is an underlying issue first.