Refactoring a monolith into services can be tricky if the application has become a tightly coupled big-ball-of-mud, but if it's been well-built (with plenty of test coverage and loosely coupled code), then it shouldn't be too taxing. There's a big difference between a well-built monolith and a big-ball-of-mud made with little thought.
It's worth expanding on test coverage, as unit tests are essential for successful refactoring without introducing regressions or new bugs. Unit tests allow you to refactor and tidy up in confidence, and they prevent the creation of code that is fragile, which developers are afraid to touch. We will cover testing in a greater detail, including automation, in Chapter 11, Monitoring Performance Regressions ...
