Horizontal scaling or scale out

In horizontal scaling, we dig deep into modules that show a higher impact on the overall performance for factors such as high concurrency; so this will enable our application to serve our increased user base, which is now reaching the million mark. We also implement load balancing to process a greater amount of work. The option of adding more servers to the cluster does not require downtime, which is a definite advantage. Each case is different, so whether the additional costs of power, licenses, and cooling are worthwhile, and up to what point, will be evaluated on a case-by-case basis. 

Scaling will be covered in detail in Chapter 8, Scaling Microservices.