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Jon Galt wonders:
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| Uhm, ok. Thanks. I guess that's clean and simple.
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| I was thinking that colo would involve some sort of coordination of
| multiple servers at different topographical (and geographical) points on
| the internet so as to minimize website downtime. (In case one is down,
| another can handle requests.) I'm actually wondering how *that* works.
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| Thanks for the clarification on colocation. Do you know anything about...
| geographically separated redundant servers? (Or whatever the appropriate
| term is.)
well, the short answer: you pay an ISP to put your server at location A,
and you pay the same or a different ISP to put a server a location B.
(and optionally, location C, D, ...). You then configure things
appropriately based on what your goals are.
typically, someone looking for geographically diverse servers has
one or both of the following goals in mind:
redundancy in the event of a failure. If a fiber is cut, natural
disaster, terrorist attack, etc. causes one server to be unable
to serve data, the other server(s) should take over and continue.
improved end-user experience. By serving data from a server closer
to the end-user, performance is improved.
both of these are "hard problems" to do well.
the former generally involves hardware or software that monitors the servers
and re-directs traffic either by re-routing the packets or by changing the
addresses returned in DNS queries.
the latter is nearly always done with "smart" DNS servers, that return the
address of the "best" server to use. Determining the "best" server involves
mapping the Internet topology and calculating metrics, often via BGP, or
ad-hoc pinging.
there are also content-delivery companies that you can outsource to. they
colocate thousands of servers scattered around the world, and have a staff
of people that analyze BGP sessions mapping the Internet.
for further reading: f5.com, akamai.com
--jeff
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