Windows Azure – Program Controlled Scaling
Software as a Service applications need to make a profit. In order to make a profit you need to effectively allocate the appropriate resources on an as-needed basis. Since Windows Azure is a pay-as-you-go service you pay for all the resources that are allocated to your application whether they are being used or not.
Windows Azure provides an almost limitless ability to scale up to handle increased traffic volume and to scale down when that volume decreases. Currently automatic scaling is not provided by Azure, however, given that Azure provides access to performance counters, queue lengths and other indicators of performance you can easily build logic into your application to control scaling.
There is an excellent article in MSDN Magazine this month on the subject: Performance-Based Scaling in Windows Azure.