Is assigning virtual server through iRule throws exception if it is offline

Hi,

Yes, make sense, but as you have only a default pool to virtual server, you can check it instead of create a pool to a single virtual server as well.

Something like this:

when <EVENT_DESIRED> {
    if { <condition is true> } {
        if { [active_members <default_pool_from_virtual_server1>] > 0 } {
            virtual <virtual_server1_name>
        } else {
            virtual <virtual_server2_name>
        }
    }
}

I hope it helps