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domain name system - If DNS Failover is not recommended, what is?

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As a followup question to his very
popular question: href="https://serverfault.com/questions/60553/why-is-dns-failover-not-recommended">Why
is DNS failover not recommended?, I think it was agreed that DNS failover is
not 100% reliable due to caching.



However the
highest voted answer did not really discuss what is the better solution to achieve
failover between two different data centers. The only solution presented was local load
balancing (single data center).



So my question
is quite simply what is the real solution to cross data center
failover?



Answer




A whole data center would need to go down or
be unreachable for this to apply. Your backup at another data center would then be
reached by routing the IP addresses to the other data center. This would happen through
the BGP route announcements from the primary data center no longer being provided. The
secondary announcements from the secondary data center would then be
used.




Smaller businesses are
generally not large enough to justify the expense of portable IP address allocations and
their own autonomous system number to announce BGP routes with. In this case a provider
would multiple locations is the way to go.



You
either have to be reached via your original IP addresses, or via a change of IP address
done by DNS. Since DNS is not designed to do this in the ways needed by what "failover"
means (users can be out of reach by at least as long as your TTL, or the TTL imposed by
some caching servers), going to the backup site with the same IPs is the best
solution.


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