Rewrite URL based on selected node for load-balancing

There's no real concept of a "node number". Pool members are defined by their IP and port. You could do something like this to "translate" the load balanced pool member into a name value based on a data group entry:

when HTTP_REQUEST_SEND {
set nodenum [class match -value [LB::server addr] equals lb_server_datagroup]
log local0. $nodenum
}

Where "lb_server_datagroup" is a data group of type string containing the pool member IPs and an associated name. Example:

10.70.0.1 := node1

10.70.0.2 := node2

10.70.0.3 := node3

Once you have this (arbitrary) name, you can change the URI, Host header, anything else.