In the mid-2010s, microservices took the software engineering industry by storm. The intent was to address modern systems’ need to change quickly, scale, and fit the distributed nature of cloud computing naturally. Many companies made the strategic decision to decompose their monolithic codebases in favor of the flexibility provided by the microservices-based architecture. Unfortunately, many such endeavors didn’t end well. Instead of flexible architectures, these companies ended up with distributed big balls of mud—designs that are much more fragile, clumpy, and expensive than the monoliths the companies wanted to break apart.

Historically, microservices are often associated with DDD, especially with the boun‐ ded context pattern. Many people even use the terms bounded context and microservi‐ ces interchangeably. But are they really the same thing? This chapter explores the relationship between domain-driven design methodology and the microservices architectural pattern. You will learn the interplay between the patterns, and more importantly, how you can leverage DDD to design effective microservices-based systems.

Let’s start with the basics and define what exactly are services and microservices.