Load balancing terminal servers w/o Session Directory

Just to clarify semantics, you said you were "load balancing 2 terminal servers", but I assume from the rest of the post you are actually LB across two RDP think clients, using 2X RDP thin clients. In either case, the issues below apply, but if you really have Windows Terminal *Servers*, then enabling Session Directory is the easiest solution to your problem.

 

 

Unfortunately, there are limitations to what you can do without Session Directory enabled. The session directory token allows a different session to check with the Session Directory server to see if there is a current connection with an RDP client pending with a server. Without that token, BIG-IP cannot maintain that persistence. Instead it uses a hash method that work as long as the user logs off properly after a session. If not, there is a x:1 chance (where "x" is is the number of RDP clients), that the thin client will connect to the correct thick client. To make matters worse, session directory is not an option with RDP clients like it is with WTS.

 

 

You may want to investigate solutions from HP known as Consolidated Client Infrastructure. HP may have some substitutions for the Session Directory server in an RDP/thin-thick client environment. Another alternative, although not available as far as I know, is to create your own "token exchange" using an iRule.