How Microsoft manages their web traffic load

Eric Schurman helps manage web performance for Microsoft's web sites. In this interview, he talks about the ways that Microsoft tries to optimize performance.

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On the web, you've got different concerns on what you have for client apps. The main things that tend to impact end-user perceived performance on the web are often things about how you've designed your application from a network perspective. So how many different HTTP get requests are you making? How are those get requests structured? So, for example, are they serialized? Did you have a Javascript file that then gets returned to the browser that requests another Javascript file and another Javascript file and then some content and then it finally gets rendered? So the number of assets that you request, that's going to be something that's important no matter what product your doing.

There are other things, like how much script do you have on the page, how much CSS you have on the page, how much actual content are your rendering to the page, etcetera. There are tricks that you can use like combining many different graphics into a single tiled image and sending that down to the browser. It's much faster to send one image to the browser than, say, 20 images. Even if you end up sending the same overall graphics, but combined into one, it's still must faster to send it as one request.

There are also different data volume concerns. They're also different from a business perspective. A lot of what we were sending out from the download center was extremely time critical. We would have an update go out, and we needed to make sure that update was going to be available anywhere in the world within a certain time frame, which required us to handle very high bandwidth, and a very high volume of requests coming into the site that were transferring lots of bits. So that required something totally different than something like the Microsoft.com homepage.

It's also interesting looking at the volume of traffic and how that traffic reflects real users. So, for example, one of the problems that you end up with on both the Microsoft homepage and Live Search is that we have a huge number of bots that are trying to hit the system, lots of people trying to do SEO work are trying to hit search engines to gather information about their site, about competitor sites, about all sorts of things. On the Microsoft.com homepage, it's always under distributed denial of service attacks. It's not a question of how frequently does it happen; it's just what is the rate right now? Also, the Microsoft.com homepage has historically had such a high up-time rate that it's actually hit by a lot of hardware devices simply to check for connectivity to the internet. And so you'd want to treat a request from that kind of "user" very differently from a request that's coming from a real user.