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Let's say I have an application that allows clients to create an account and put a form on their site that allows people to create tickets. With 475 clients who have websites with forms. They get about 100 form submissions per day per account (47500 total tickets per day on average). If you assume that all of those take place during only 8 hours of the day, it comes to only 1.6 or so tickets per second.

If I was shopping for a load balancer, does this mean that I only need one that can handle 5 SSL TPS? This seems ridiculous to me?

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2 Answers 2

up vote 3 down vote accepted

Your average connections per second isn't the important thing; it's the peak you've got to be worried about. For that, you need better statistics on what your load patterns will look like. If you don't have that, I usually use a 4:1 peak/average ratio across the 24-hour average (so for you, you're looking at 1.6 / 3 * 4` -- 3 to get to the 24 hour average, 4 to get the peak from the average -- a bit over two connections per second at peak).

This ratio, by the way, simply comes from my experience with sites with geographically localised userbases (like you suggest). I've got other ratios for global userbases and "known peaky" sites. If you take the worst case, a really peaky site, I use a ratio of 10:1, so you're still only looking at a bit over five connections per second.

Like Andrew says, at that sort of volume you shouldn't even be breaking a sweat on one machine. I've got a site that does handles several hundred HTTP(S) connections per second per machine (a dynamic-heavy site, with a lot of SSL connections) -- obviously that's going to vary a lot by your codebase, but if you need to load balance five SSL connections per second, something is very, very wrong.

Personally, I don't like SSL accelerated load balancers, as in my experience they just make for a whole new bottleneck -- when your site gets popular enough, the SSL accelerator won't be able to keep up (and upgrading those things gets expensive). I prefer a simple TCP load balancer, where I can simply scale out my backends as they reach capacity (whether it's because of SSL connections or just processing requests).

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Your math is correct. Do you even need a load balancer at that volume?

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Does that seem logical to have that little need for load and connections with so mNy clients? I'm just so confused about where IT budgets go at this rate. You're sure there aren't other factors I'm forgetting? –  orokusaki Jan 12 '10 at 8:13
    
This is a manual process... if you have machines hammering on your server, as for a file server, or tens of thousands of users, then you start needing serious capacity. –  Andrew McGregor Jan 12 '10 at 11:20

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