In this chapter, we discussed microservices, MSAs and reactive architectures, as well as the principles of SOAs. We learned how to modernize an application, thus transforming a monolith into an MSA. We also reviewed how the main opensource frameworks, like Spring and Vert.x, have implemented reactive principles in order to help developers build cloud-oriented applications that are scalable, reliable, and cost-effective. Finally, we learned how you can update your traditional JEE applications in order to implement an asynchronous and non-blocking system as the first step toward building your own MSA. 

In the next chapter, we will look at cloud-native applications and microservices so that we can understand how to design and implement them.