hostcheckloop(): Timeout includes DNS lookup which causes havoc on resolver reboots

[ZNikke]

redirprg/redirprg.pl

Line 892 in 1355b6f

my $resp = $ua->head("http://$hosts->[$i]->{fqdn}$uri");

assumes that DNS is quick, but since the check is done against FQDN DNS can have a big impact and
actually cause timeout if the primary resolver is unreachable.

This might trigger failure storms causing all offloaders to pop offline making the frontends trying to handle all traffic. This in turn causes a caching storm, which causes significant load on the backend.

The fix is to do DNS lookup separately and do HEAD using the resolved IP address.