Scalability

Running applications and systems that are available to users for consumption is important for architects of any serious application. However, there is another equally important application feature that is one of the top priorities for architects, and this is the scalability of the application.

Imagine a situation in which an application is deployed and obtains great performance and availability with a few users, but both availability and performance degrades as the number of users start begins to increase. There are times when an application under normal load performs well, but degrades in performance with the increase in the number of users. This can happen if there is a sudden increase in the number of users and the environment is not built for such a large number of users.

To accommodate such spikes in the number of users, you might provision the hardware and bandwidth for handling spikes. The challenge with this is that the additional capacity is not used for a majority of the year and does not provide any return on investment. It is provisioned for use only during the holiday season or sales. I hope you are getting to know the problems architects are trying to solve. All these problems are related to capacity sizing and the scalability of an application. The focus of this chapter is to understand scalability as an architectural concern and to check out services provided by Azure for implementing scalability.

Capacity planning and sizing are a few of the top priorities for architects for their applications and services. Architects must find a balance between buying and provisioning too many resources versus fewer resources. Having fewer resources can lead to not being able to serve all users, turning them to the competition, while having more resources can hurt your budget and return on investment because most of the resources remain unused most of the time. Moreover, the problem is amplified with a varied level of demand during different times. It is almost impossible to predict the number of users for the application round the clock and year. However, it is possible to find an approximate number using past information and continuous monitoring.

Scalability refers to:

Scalability refers to the ability to handle a growing number of users and provide them with the same level of performance when there are fewer users in application deployment, processes, and technology. Scalability might refer to serving more requests without degradation of performance, or it might refer to handling larger and more time-consuming work without any loss of performance in both cases.

Capacity planning and sizing exercises should be undertaken by architects at the very beginning of the project during the planning phase to provide scalability to applications.

Some applications have stable demand patterns, while it is difficult to predict others. Scalability requirements are known for stable demand applications, while it is a more involved process for variable demand applications. Auto scaling, a concept we will review in the next section, should be used for such applications whose demands cannot be predicted.