DNS anycast node monitor

[Phil Mayers]

On 09/04/15 15:50, Hillary Nelson wrote:
> Currently we have about 20 DNS servers sit behind two pairs of F5 LTM on
> campus, the two pairs of F5s using router injection for DNS virtual
> addresses. This setup is costly and we are trying to use direct anycast
> between router and server instead, with quagga and bgp.

Consider using exabgp. It can run scripts as a sub-process that echo 
"advertise" and "withdraw" commands or toggle the status of a "watchdog" 
which can be trivially used to do this kind of service check-based route 
advertisement, and you don't have to actually change the OS routing 
table (and incur an rndc reconfig) which is win IMO.

Example would be something like:

neighbour x.x.x.x {
   peer-as ...
   ...

   static {
     route x.x.x.x/32 next-hop ... watchdog blah;
   }
   process foo {
     run /usr/local/bin/...
   }
}

...and your script would be:

#!/bin/sh

VIP="<the IP bind is anycasted on>

while true; do
   # ensure we're talking to the local virtual IP
   dig -b 127.0.0.1 @$VIP example.com soa >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
     echo announce watchdog blah
   else
     echo withdraw watchdog blah
   fi
   sleep 1
done