In this section, we will describe the basic principles of microservices and their features, and present the benefits and the drawbacks of this new way of designing and building applications.

Microservice architecture is based on the concept that an application should contain a collection of loosely coupled, independent, and atomic services, which implement business capabilities. Using this approach, it's easy to build software that splits a big enterprise application, also known as a monolith, into smaller and consistent contexts, known as microservices.

It also enables the fast evolution of a company's technology stack, thanks to the building of autonomous...

Service-oriented architecture is a way to design software where the business services communicate through a standard communication protocol, usually Simple Object Access Protocol (SOAP), over a network. The main target of an SOA is to be independent of vendors, products, and technologies. The principal unit of an SOA is the service—a small unit of functionality that can be accessed remotely, and acted upon and updated independently.

The communication between services happens via direct exchange of data or it could involve two or more services that are coordinated by an orchestrator, Enterprise Service Bus (ESB) that is responsible for managing the execution flow.

There are two main roles in an SOA—a service provider and a service consumer. The first one is the service that's defined within the SOA while the second one is the point where consumers...

Usually, large organizations have already invested a large number of resources in existing monolith applications that represent the core of their business.

According to Gartner research (Kurt Potter, Sanil Solanki, and Ken McGee, Run, Grow, and Transform the Business IT Spending: Approaches to Categorization and Interpretation, Gartner G00308477, June 27, 2016):

Besides, there are also some examples, such as the one described in The Majestic Monolith (https://m.signalvnoise.com/the-majestic-monolith-29166d022228), that demonstrate that a monolith application is not the devil like someone has said.

So, why tear down the monolith?

The response is always the same. In most cases...

The term reactive is widely used in the definition of MSAs.

But what is a reactive architecture based on? The definition of reactive is to give an answer after a stimulus. Reactive software is, therefore, able to adapt its behavior and react to receive stimuli.

To build a reactive architecture for microservices, the following models must be combined:

• Reactive programming: A development model based on the observation of streams of data, which provides a way to react to their changes and propagate them toward other actors
• Reactive system: An architectural model that is used to build robust and highly reactive distributed systems based on asynchronous communication using messages

The definition of a reactive system was formalized, in version 2.0, in September 2014 through the reactive manifesto (https://www.reactivemanifesto.org/). The...

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.