one requirement in LB

How are you going to know to set that? With some sort of process running on the server or the sending application?

 

 

Then now are you going to know if a server has been upgraded or not before / when a load balancing decision is made?

 

 

I was thinking something more along the lines of different Data Groups and Pools.

 

 

Data Groups to differentiate the upgraded and non-upgraded requesting servers (so that no other mechanism would be necessary to determine if a server had or had not been upgraded) and pools to separate the upgraded and non-upgraded (otherwise you would not be able to keep the load equal on a group of servers).