ProxyPass - Reverse Proxy / Backend URL rewrite.

when HTTP_REQUEST {
if {[string tolower [HTTP::host]] starts_with "service.mycompany.com" } {
HTTP::redirect http://externalsite.longurl.application.service.othercompany.com[HTTP::uri]
}
}

when HTTP_REQUEST {
if {[string tolower [HTTP::host]] starts_with "service.mycompany.com" } {
HTTP::redirect http://externalsite.longurl.application.service.othercompany.com[HTTP::uri]
}
}

when HTTP_REQUESTED {

    if { [HTTP::host] eq "www.yahoo" } {
          NAME::lookup www.google.com
         Wait until name resolution is completed before sending you to the new page  
        HTTP::collect
        }
}

when NAME_RESOLVED {
   set response [NAME::response]
   resolved www.google.com to an ip address via load balancer and now use that in the node command.
 
  switch [llength $response] {
      0 {
          HTTP::respond 500 content "Couldn't Process Request}
      default {
             HTTP::uri "[HTTP::uri]"
              HTTP::header replace "Host" "www.google.com"
             node [llindex $response 0] 80
          }
   }
HTTP::release
}