Building Global Web Applications With the Windows Azure Platform – Introduction

I don’t know if you noticed, probably not, but I’ve put some content again on http://www.goeleven.com. This content will serve as a starting point to a new series that I’m writing. In this series I will discuss, step by step, what it takes to build global, highly scalable, highly available, high density and cheap web applications with the windows azure platform.

In this first stage I’ve just built a simple web application, using asp.net MVC, with some fairly static content: a razor layout page, a static content body, a css file, some images, nothing fancy… All of this is configured in an extra small webrole uploaded to http://goeleven-eu.cloudapp.net with only 1 instance. (http://www.goeleven.com is mapped to this address using a CNAME record at my DNS provider).

The general idea behind this series is to build on top of this basic sample, with more functionality and more windows azure features, and try out how the application will behave in the real world, in terms of performance, scalability, availability and so on. In order to achieve this we need to be able to simulate some real life load on our application, so I signed up at http://loadimpact.com which allows me to setup load tests with up to 5000 simulated users.

In a very first test I will ramp up to 50 concurrent users and see if this miniature application can handle it. 50 concurrent users means about a 1000 visits per hour (given that the average stay time is about 3 minutes), or 24000 visitors per day, this should definitly do for my simple site at this stage…

Note: If you want to derive the average number of concurrent users currently on your site, you can use the following formula: concurrent_users = (hourly_visits * time_on_site_in_seconds) / 3600

Now let’s have a look at the results:

1 Extra Small Instance - 50 Concurrent users

As you can see, the site survived the onslaught, albeit barely. There is a significant decline in performance when the number of concurrent users increases over 30, and an almost 300% increase in response time once we reach 50 concurrent users. I’m quite sure the site would actually break down if we increased the numbers only a bit more.

Breaking down is a subjective concept on the web, it does not mean that the webserver actually crashes, it means that the users go away from the page they were intending to visit. This graph shows the average load times for all of the users. Average really means that 50% of the requests took more than the amount of time displayed in the graph. Personally I consider a site broken if it’s requests take more than 3 seconds to load on average, which means 50% of it’s users had to wait more than 3 seconds before they got a response (which they won’t do anymore).

So what can we do to handle this problem? How can we serve more people? We either scale up or scale out, right?

If this is your first reaction, you didn’t get the utility model yet…

Utilities, like windows azure, are all about optimal use of capacity. Windows azure roles offer an array of different kinds of capacity (compute, memory, bandwidth) and I bet that not all of these are optimally used yet and only one of them is the bottleneck…

Next time we will look into this capacity topic a bit further and see how we can get some more juice out of this instance without having to pay a lot more…

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