On 19/4/2013 1:12 μμ, kalpesh thaker wrote:
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.
Thanks,
I have been discussing this on the Dovecot mailing list, and Timo
(Sirainen) said:
Well, there are two failure reasons:
a) Dovecot server fails. For that, you could use any kind of a proxy
that redirects traffic to the other server (even Dovecot proxy on
another server).
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.
Nick.
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