Capacity planning and sizing are one of the top priorities for architects for their applications and services. Architects must find a balance between buying and provisioning too many resources versus less resources. Having fewer resources can lead to not being able to serve all users, turning them off to competition, while having more resources can hurt the budgets and return on investments because most of these resources remain unused most of the time. Moreover, the problem is amplified with 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 continues monitoring.
According to Wikipedia (https://en.wikipedia.org/wiki/Scalability), scalability refers to: