Providing Scalability for ASP.NET Applications

By Iqbal Khan

The popularity of ASP.NET, the Web application framework from Microsoft, continues to grow by leaps and bounds within the developer, enterprise, and IT ranks. There is one area of difficulty, however: scaling ASP.NET applications out of the box is simply not possible.

Scalability has two meanings in this context. First, you need to be able to effectively handle peak user loads because every application goes through peaks and valleys in terms of the number of users logged in at any point in time. When you design the infrastructure, you want to design the application so it can handle the peak loads as efficiently and as fast as nonpeak loads.

Second, you have to be able to increase the total capacity of your system. Today you may have only 5,000 users. Six months, a year down the road, you may have 10,000 or 15,000 or 20,000, and in a few years you could end up with 100,000 users. Being able to grow with the number of users without grinding the application to a halt is what scalability is all about. It means you are able to add more users without negatively impacting the performance in any noticeable way or, if there is any degradation, it should be within an acceptable range.

A typical ASP.NET application is deployed on one or more Web servers that are linked together in a Web farm, with a load balancer that distributes traffic to all the Web servers. In theory, the more Web servers you add, the more requests you should be able to process per second. The architecture of a Web farm is meant to give scalability to ASP.NET. That's the theory; the reality is a bit different.

The problem for ASP.NET applications is that while Web technology provides an elegant architecture of Web farms and load balancers, data storage technologies have not kept up. Certainly you can scale out in a Web application by adding more servers or by increasing the strength of individual servers with more memory and CPU power.

But as you do that, data storage is not able to scale in the same proportions. It does scale, but not as much as the Web application tier. Consequently, anything in your ASP.NET application associated with data storage or data access is a potential scalability bottleneck. More to the point, a database server does not scale for either sessions or applications data.