On 25/07/2019 22:17, Giles Coochey wrote: > > Separate DNS servers must be on a different subnet according to > RFC2182 (https://tools.ietf.org/html/rfc2182): > > Secondary servers must be placed at both topologically and > geographically dispersed locations on the Internet, to minimise the > likelihood of a single failure disabling all of them. > > I know that UPSs are physical, and subnets are logical, but the > reasoning behind the requirement is due to having to be on a different > infrastructure. > > __ Shock horror, replying to my own post, but in cloud cluster environments, you might consider anti-affinity rules to prevent multiple name servers going down at the same time due to a cluster node failure (i.e. rules to ensure that hypervisors keep different name servers on different hosts). I know it doesn't help OP, who was looking for cluster based solutions, but the same applies if using load balancing virtual appliances, hosting IPs as name servers.