iRule replace HTTP Host header for virtual Host

Try this, it works for me:

Create a Datagroup partnering Ip + name (SERVER HOST HEADER) from servers you want to load balance.

After create this, copy this iRule and change "name_datagroup" you have previously created.

when HTTP_REQUEST_SEND {

  clientside {

      set host_header_value [class match -value [IP::server_addr] equals **name_datagroup**]

        Check if the lookup returned a value
      if {$host_header_value ne ""}{

          Replace the host header value
         HTTP::header replace Host $host_header_value
          }
   }
}