As a followup question to his very popular question: 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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