What are microservices?

When an application is maintained by many different developers over a longer period of time, it tends to get more and more complex. Bug fixes, new or changing requirements, and constant technological changes result in your software continually growing and changing. When left unchecked, this software evolution will lead to your application getting more complex and increasingly difficult to maintain.

Preventing this kind of software erosion is the objective of the microservice architecture paradigm that has emerged over the past few years. In a microservice architecture, a software system is split into a set of (potentially a lot of) independent and isolated services. These run as separate processes and communicate using network protocols (of course, each of these services should in itself be a twelve-factor app). For a more thorough introduction to the topic, we can recommend the original article on the microservice architecture by Lewis and Fowler at https://martinfowler.com/articles/microservices.html.

In contrast to traditional Service-Oriented Architectures (SOA), which have been around for quite a while, microservice architectures focus on simplicity. Complex infrastructure components such as ESBs are avoided at all costs, and instead of complicated communication protocols such as SOAP, simpler means of communication such as REST web services (about which you will learn more in Chapter 2, Building Microservices Using Rest APIs) or AMQP messaging (refer to Chapter 4, Asynchronous Microservice Architectures Using Message Queues) are preferred.

Splitting complex software into separate components has several benefits. For instance, different services can be built on different technology stacks. For one service, using Go as runtime and MongoDB as persistence layer may be the optimal choice, whereas a Node.js runtime with a MySQL persistence might be a better choice for other components. Encapsulating functionality in separate services allows developer teams to choose the right tool for the right job. Other advantages of microservices on an organizational level are that each microservice can be owned by different teams within an organization. Each team can develop, deploy, and operate their services independently, allowing them to adjust their software in a very flexible way.