Microservices Architecture

The microservice architecture is an architectural style that structures an application as a set of loosely coupled, services organized around business capabilities.

The goal of the microservice architecture is to accelerate software development by enabling continuous delivery/deployment.

Microservice Success Triangle

The microservice architecture does this in two ways:

Simplifies testing and enables components to deployed independently
Structures the engineering organization as a collection of small (6-10 members), autonomous teams, each of which is responsible for one or more services

These benefits are not automatically guaranteed. Instead, they can only be achieved by the careful functional decomposition of the application into services.

A service must be small enough to be developed by a small team and to be easily tested. A useful guideline from object-oriented design (OOD) is the Single Responsibility Principle (SRP). The SRP defines a responsibility of a class as a reason to change, and states that a class should only have one reason to change. It make sense to apply the SRP to service design as well and design services that are cohesive and implement a small set of strongly related functions.

The application also be decomposed in a way so that most new and changed requirements only affect a single service. That is because changes that affect multiple services requires coordination across multiple teams, which slows down development. Another useful principle from OOD is the Common Closure Principle (CCP), which states that classes that change for the same reason should be in the same package. Perhaps, for instance, two classes implement different aspects of the same business rule. The goal is that when that business rule changes developers, only need to change code in a small number - ideally only one - of packages. This kind of thinking makes sense when designing services since it will help ensure that each change should impact only one service.

When designing a solution with Microservices, there are a series of questions that will need to be addressed:

How to decompose an application into services?
How to deploy an application’s services?
How to handle cross cutting concerns?
Which communication mechanisms to use?
How do external clients communicate with the service
How does a client discover the network location of a service instance?
How to prevent a network or service failure from cascading to other services?
How to maintain data consistency and implement queries?
How to understand the behavior of an application and troubleshoot problems?
How to make testing easier?
How to implement a UI screen or page that displays data from multiple services?

Before you begin, you must start somewhere. It starts with the Business Challenge. What problem or opportunity are you trying to address. From there you will want to decompose the application into services. See below for more details and the appropriate design pattern(s) to help answer these questions.