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copied!<p>You would probably have to be on the engineering team at one of these places to know for sure but there are people who have made educated guesses from talks and other information that has come out of both places:</p> <p><a href="http://highscalability.com/ebay-architecture" rel="nofollow noreferrer">Ebay Architecture</a> and <a href="http://highscalability.com/amazon-architecture" rel="nofollow noreferrer">Amazon Architecture</a></p> <p>Just a single load balancer by itself in today's world is kind of the equivalent of DNS round robin of years past. Today you have things like <a href="http://en.wikipedia.org/wiki/Anycast" rel="nofollow noreferrer">anycast</a> that let you play all kinds of tricks. You can be pretty sure that the likes of ebay and amazon do use load balancers and they use a lot of them.</p> <p>You may want to boil it down a little more when you think about how it might work because a lot of the traffic is stateless. In a single request for a page there are potentially a lot of objects that don't need to know about the state. Take those objects out of the picture by serving them from a stateless system (this is where the anycast comes in) and the number of requests goes down dramatically. </p> <p>If that doesn't get you to the point that a single load balancer can handle the load then the next step up is to break the transactions up using IP routing and/or geo-DNS. Sites as large as ebay and amazon will be in a number of different datacenters with a large number of internet connections at each. You take everything coming in from internet pop quest-west and send it to the west coast datacenter "quest" servers, anything from att-west gets sent to the west coast datacenter "att" servers, anything from quest-east and it goes to the east coast datacenter "quest" servers, etc. Each of those systems could be an island a single load balancer that could handle the load, some of the load balancers out there can handle hundreds of thousands of transactions a second even SSL encrypted. On the backside you replicate in bulk to each datacenter constantly but it can be out of sync.</p>

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