Scalability is the ability of the application to handle an increase in workload without performance degradion, or its ability to quickly enlarge. It is the ability to enlarge the architecture to accommodate more users, more processes, more transactions, and additional nodes and services as the business requirements change and as the system evolves to meet the future needs of the business. The existing systems are extended as far as possible without replacing them. Scalability directly affects the architecture as well as the selection of hardware and system software components.

The solution must allow the hardware and the deployed software services and components to be scaled horizontally as well as vertically. Horizontal scaling involves replicating the same functionality across additional nodes; vertical scaling involves the same functionality across bigger and more powerful nodes. Scalability definitions measure volumes of users and data the system should support.