Error page if a FQDN node is unavailable

Then try the following:

when HTTP_REQUEST {
    set dest [RESOLV::lookup @8.8.8.8 -a FQDN-of-the-node]
    log local0.info "destination address : $dest"
    if { $dest ne "" } {
        node $dest
        log local0.info "node used : $dest"
    } else {
        HTTP::fallback "http://host.domain.com/redirect.html"
    }
}

.