iRule catch all - to redirect if no pool selected

You can change your irules like that

Pool_Selection_iRule:

when HTTP_REQUEST {        
    HTTP::host [string tolower [HTTP::host]]
    catch { pool  "[HTTP::host]_pool"}
}

Sorry_Page_iRule:

when HTTP_REQUEST priority 900 {        
    set dpool [LB::server pool]
    if { $dpool equals "" } { HTTP::redirect "http://sorry_page.com" ; unset dpool; return}
    if { [active_members $dpool] == 0 } { HTTP::redirect "http://sorry_page.com"; unset dpool; return}
    unset dpool
}

when LB_FAILED {
    log -noname "[virtual name] DEBUG: Server Pool: $PoolName SELECTED"
    if { [active_members [LB::server pool]] == 0 } {
    log -noname "Sorry Page Activated / Server Pool: $PoolName selection failed on  connection attempt from [IP::client_addr]"
    HTTP::redirect "http://sorry_page.com"
}