Application Transition

If you just want 10% of traffic to go to the new app and you don't care which 10%, you could put new web app servers in the pool and do weighted ratio load balancing. Just make sure you have a persistence profile so that people aren't being bounced back and forth between old and new.

If you want to have specific people go to the new app, then you'll have to decide how you want to identify them. Say you want to identify them by IP address. In that case you could create a data group of IP addresses that should get the new site, then have an iRule something like this:

when CLIENT_ACCEPTED { if { [class match [IP::client_addr] equals new_web_app_class] } { pool new_web_app_pool } else { pool old_web_app_pool } }

You could also identify them by cookie or by some other more exotic method.