irule Troubleshooting:

try this:

 when RULE_INIT {
    set static::sorry_pool "/Common/pool_wwbtest_sorry"
    set static::wartung_pool "/Common/pool_wwbtest_wartung" 
}

when HTTP_REQUEST {
log local0. "Incoming URI = [HTTP::uri]"
    if { [active_members [LB::server pool]] < 1 } {

            if { [active_members $static::wartung_pool] > 0 } {
                    pool wartung_pool
                    set mypick [LB::select]
                    log local0. "The LB choice is: $mypick"
                    set newuri [string map {/wartung.html/ /} [HTTP::uri]]
                    log local0. "The new URI is = $newuri"
                    HTTP::uri $newuri
                    eval "GET [HTTP::uri $newuri] HTTP/1.1\r\nHost: $mypick\r\n\r\n"
                    log local0. "[HTTP::uri] [LB::server addr]" 

                } elseif { [active_members $static::sorry_pool] > 0 } {
                    pool sorry_pool
                    set mypick [LB::select]
                    log local0. "The LB choice is: $mypick"
                    set newuri [string map {/sorry.html/ /} [HTTP::uri]]
                    log local0. "The new URI is = $newuri"
                    HTTP::uri $newuri
                    eval "GET [HTTP::uri $newuri] HTTP/1.1\r\nHost: $mypick\r\n\r\n"
                    log local0. "[HTTP::uri] [LB::server addr]" 
                            } else {
                            HTTP::respond 200 content "Lieber Kunde,\r\ndie Seite befindet sich aktuell in der Wartung.\r\n\r\nDear Customer,\r\nthis site is down for maintenance. We are sorry for the inconvience.\r\n" noserver connection close
        }                   
    }
}