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.
Hi,
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/
regards,
kalpesh
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