[Pdns-users] DNS Failover

kalpesh thaker kalpesh at webdevworld.com
Fri Apr 19 10:12:30 UTC 2013

> We have two SMTP/POP/IMAP/Apache(Webmail) Servers, say 
> mail1.example.com and mail2.example.com and we want to implement 
> DNS-based failover. mail1.example.com is the main one; in case of 
> mail1.example.com failure, DNS should redirect users as soon as 
> possible to mail2.example.com.


 From my personal experiences, DNS failover does not always work as you 
would expect... mainly because you wont have much control over 3rd party 
recursors and of the way they cache TTL values. and by the time DNS does 
propogate... your mail server CNAMEs could have changed again, so you'd 
therefor have mail arriving at both servers etc.

I'd recommend looking into adopting HA strategies rather (with tools 
such as hearbeat and internal dynamic DNS which can change IPs on the 
fly within your local network according to availability) than rely on 
public DNS for failover.

There is quite alot of info about HA at http://www.linux-ha.org/



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