[Pdns-users] DNS Failover

[Darren Gamble]

Hi Nikolaos,

>     b) Network connection to the whole data center dies, or the whole
>     data center loses power or otherwise dies. There's really no other
>     choice to failover that than DNS, unless you manage to route the
>     same IP address to two different data centers and just update the
> route.
> 
>     I'd be more worried about b), since you can already fix a) pretty
>     quickly with VMs. Or a) could also be switched to become a Dovecot
>     proxy on demand if there's a bigger problem that can't be
>     immediately fixed.
> 
> ...and, yes, it's case "b" I want to handle. So that leaves me with DNS
> solutions.

You are indeed on the right track.  If you have two datacenters with different IP networks, your options are limited, but DNS is one of them.

You can use the CNAME suggestion you gave here (with low TTL) or you can simply have it return the right A record directly (also with low TTL).  You would have some sort of keepalive in the background making updates to your backend as appropriate.  This is a not-uncommon configuration.  Assuming your DNS server can handle the load, this is very robust.

It sounds like you've already got most of this figured out.  You just need to write your is-it-alive script and have it update your pdns backend as appropriate.  Don't have your backend do the query on demand- this does not scale.

     - Darren -