Directing traffic based on query parameter

As Steve relates, you need some (unfortunately manual) approach to mapping the web server's name to a node address. This can usually be done with a string-based data group. Example:

Data group (ex. my_webserver_dg):

"web-server1" := "10.10.10.10 80"
"web-server2" := "10.10.10.11 80"
"web-server3" := "10.10.10.12 80"
"web-server4" := "10.10.10.13 80"
"web-server5" := "10.10.10.14 80"

And then an iRule that looks for the query string and routes accordingly, otherwise uses standard persistence:

when HTTP_REQUEST {
    if { [string tolower [HTTP::uri]] starts_with "/myarticle.php?s=" } {
        set webserver [URI::query [string tolower [HTTP::uri]] s]
        if { [class match $webserver equals my_webserver_dg] } {
            set nodelist [split [class -value match $webserver equals my_webserver_dg] " "]
            node [lindex $nodelist 0] [lindex $nodelist 1]
        }
    }
}