redirecting links to a maintenance page on 1 virtual server

when HTTP_REQUEST {

   set uri [HTTP::uri]
}

when LB_FAILED {

    A load balancing attempt failed.  Check if the current selected pool has any members.
   if { [active_members [LB::server pool]] == 0 } {

       Check the requested HTTP URI with wildcard support
      switch -glob $uri {
         "/app1*" {
             URI started with /app1
             Save the fallback URI as app1_site
            set uri "app1_site"
         }
         default {
             URI didn't start with /app1
             Save the fallback URI as app2_site
            set uri "app2_site"
         }
      }

       No active members, so use the dynamically set fallback URL
      HTTP::fallback "HTTP://maintenance.domain.com/$uri"
   }
}