Uinsing irules to fileter via uri context

Can you show us your iRule? Are you trying to route the traffic to the different applications based on a condition of the request (ie. URI, port, etc.)? If there are 4 different application servers in a single pool, how do you load balance?

In many cases admins will put the applications into separate pools and then switch pools on the request condition (like the URI).

when HTTP_REQUEST {
   switch -glob [string tolower [HTTP::uri]] {
      "/contexta*" { pool contexta_pool }
      "/contextb*" { pool contextb_pool }
      "/contextc*" { pool contextc_pool }
      default { pool default_pool }
   }
}

In this way you can provide both load balancing for multiple application servers in a pool, and monitoring.