As developers, we always try to create reusable components to interact with systems or services in order to avoid writing code more than once. Most monolithic applications that we have built so far have followed a three-tier architectural pattern, as shown in the following diagram:
Three-tier architecture
When a change is required in an application that is built using this model, you often need to modify all three layers. Depending on how the application is created, you might need many deployments. Furthermore, since large monolithic applications share a lot of functionality, it's common to find more than one team working on them, which makes it even harder for them to evolve quickly. Sometimes, specialized teams work on particular layers because these layers are comprised of many components. In this way, changes are applied horizontally to make the application grow and evolve.
With microservices, applications evolve vertically because they are modeled around a specific...