Scalability Requirements

In IT systems scalability means the ability to increase a system's capacity (throughput) by adding resources like CPU, Memory, Disks and increasing Network capacity to support more users and / or more concurrent transactions.

The two main types of upscaling are

• Scale up – typically adding CPU's and / or Memory to one server
• Scale out – adding additional servers

The crucial questions are:

If I add a 2nd CPU (or even more) into the server or purchase a server with more CPU's

• can the application utilize the additional CPU's?
• will my single long running report or batch job utilize more than one CPU and finish in less time?

If I purchase a 2nd server

• Is the application designed for multi-server deployment?
• Would using an external workload balancer distributing requests to 2 servers end up in duplicate customer-ID's ?

You see that this is a complex topic....

To ensure that the application will scale according to your needs, the detailed requirements need to be carefully selected and formulated.

Our “Template for Non-Functional Requirements” dedicates one chapter to scalability-requirements.