Micro Services - Spring Boot, Eureka and Feign - Part 1

Micro Services

The term 'Micro Service' is the current flavour of the month within software circles. However, this approach to architecture; splitting up applications into small units of functionality is nothing new. As developers and architects we always look to decouple our systems into single, simple units of functionality. This is a basic principle of OO. The philosophy of Micro Services is to decouple units of functionality entirely. Each unit should effectively standalone in its own environment with as little, or no, dependency on others. Again, this isn't a new approach. Since the advent of web services, inparticular REST, we have decoupled our systems into simple, stateless, independently scalable applications. The advantages of this are clear but as our systems grow into transient environments it becomes difficult for each application to keep track on service end points of other systems. The big win of the Micro Service approach is automatic discovery which helps DevOps solve the headache of configuration across the ecosystem.

In part 1 of this blog I will use Spring Boot to set up a Micro Service very quickly and easily and run it in the cloud. In part 2 I will configure this service to register itself for auto discovery and create a client which has no configuration dependency on the service. This is accomplished with Spring Cloud, Netflix Eureka and Feign; three important frameworks which make up the basis of Spring's Micro Service implementation.

Creating a Micro Service with Spring Boot

Spring Boot allows us to create a deployable application at the drop of a hat. There's no need for a external web server or servlet container, Spring Boot takes care of all that and allows us to just execute a jar file to run a web service. Spring Boot employs the common Spring philosophy of convention over configuration, often to the extreme. This results in an annotation rich framework with little, or no, xml or properties to configure.

To demonstrate this we'll start with a simple REST service which will return a 'hello world' string to a GET request. As with all applications, start with the Maven build file - pom.xml and import into your favorite IDE.

The key here is the parent - spring-boot-starter-parent. This brings in all the dependencies and environment configuration you need to run a Spring Boot app. The only additional dependencies I've added are the web and test packages because this application will be a web app for which I want to write some unit tests. Once imported, create a package structure and add a class name 'Application' with a main method.

By default, the SpringBootApplication annotation enables component scan for its own and sub packages. Therefore, it is convention to add our other components to packages below this one. Create a web and service package for our MVC controller and service layer classes.

The MVC controller and service are both very simple as you'd imagine. Amongst other things, Spring Boot includes automatic configuration of Spring MVC, which is again enabled by the SpringBootApplication annotation. This means its a simple case of just annotating the controller as a RestController and adding the mappings. The HelloService simply returns a string saying hello

That pretty much concludes the service. The only other addition is a properties file. By default, Spring Boot will look for a file named application.properties on the root classpath. This file will hold any other configurations which are required in subsequent parts of this blog. For now, we just add a name for the service, like so.

To run the application as a web service we need an environment hosting the JDK 1.8. No application server is required as Spring Boot has an embedded pre-configured tomcat. If you have an AWS account, spin up a micro instance, ensure you are running Java 1.8 and add the following line as user data to run the HelloService

Open a browser and navigate to the instance on the default 8080 tomcat port. The browser, by default, will issue a GET request and return the message from the service.