Introduction to Microservices Using Spring-Boot

Microservices enable different teams to work on smaller pieces, using independent technologies, producing safer, more frequent deployments

Introduction

If you are not already using Microservices, you are safely out of the early adopter phase of the adoption curve, and it is probably time to get started. In this article, we will demonstrate the essential components for creating RESTful microservices, using Consul service registry, Spring Boot for all the scaffolding, dependency injection, and dependencies, Maven for the build, and Spring REST.

Over the last two decades, enterprise has become very agile in our SDLC process, but our applications tend to still be rather monolith, with huge jars supporting all of the varied APIs and versions in play. But nowadays there is a push towards more Lean, DevOps-ey processes, and functionality is becoming “serverless”. Refactoring to Microservices can decouple code and resources, make builds smaller, releases safer, and APIs more stable.

Prerequisites

Purpose

In this post, we will build a simple geospatial application that clients can call with two spatial points. The points microservice will send the points the client submitted to a distance microservice to calculate the distance between the given points, and then return the result to the points service, exposing all that via a rest call.

Architecture

Microservice Architecture

Project Structure

At the end of this guide our folder structure will look similar to the following:

.
|__distance/
|  |__src/
|  |  |__main/
|  |  |  |__java/
|  |  |  |  |__com/
|  |  |  |  |  |__juliuskrah/
|  |  |  |  |  |  |__distance
|  |  |  |  |  |  |  |__DistanceApplication.java
|  |  |  |__resources/
|  |  |  |  |__application.yaml
|  |  |  |  |__bootstrap.yaml
|  |__pom.xml
|__points/
|  |__src/
|  |  |__main/
|  |  |  |__java/
|  |  |  |  |__com/
|  |  |  |  |  |__juliuskrah/
|  |  |  |  |  |  |__point/
|  |  |  |  |  |  |  |__PointsApplication.java
|  |  |  |__resources/
|  |  |  |  |__application.yaml
|  |  |  |  |__bootstrap.yaml
|  |__pom.xml

Before we get to work on creating our microservices, let’s prepare our environment by setting up Consul.

Download Consul Service Registry

We will be using Hashicorp Consul for service discovery, so head over to https://www.consul.io/downloads.html and download Consul, for Windows, Linux, Mac, etc. That will provide an executable that you will want to add to your path.

From a shell prompt, launch Consul in dev mode:

PS C:\> consul agent -dev

If you prefer to use docker, here’s the command to start consul in dev mode:

PS C:\> docker run -d --name=dev-consul -e CONSUL_BIND_INTERFACE=eth0 consul

To verify that it is running, head over to a browser and access the consul UI http://localhost:8500. If all is well, consul should report that it is alive and well.

Consul Up

Consul running on port 8500

If there are any issues at this point, be sure ports 8500 and 8600 are available.

Create the SpringBoot application

We will use Spring Intitializr to create the scaffolding for our SpringBoot applications. Head over to the Spring Initializr webapp and create the distance microservice. Select Web and Consul Discovery then click Generate Project to download a zip file. Extract this zip file and load the project into your favorite IDE or text editor.

Distance Service

Generate Distance Microservice

We can use the generated application.properties, but Spring-Boot also recognizes YAML format, and that’s a little easier to visualize, so let’s rename it application.yaml. Also create a bootstrap.yaml file.

We will name the microservice distance. We can specify a port or use port 0 to have the application use an available port. In our case we will use 57116. If you deploy this service as a Docker container you will be able to map that to any port of your choosing. Let’s name the application in bootstrap.yaml and specify our port by adding the following to our application.yaml:

file: distance/src/main/resources/application.yaml

server:
  port: 57116
spring:
  cloud:
    consul:
      discovery:
        register-health-check: false

file: distance/src/main/resources/bootstrap.yaml

spring:
  application:
    name: distance

Now build the project, and run it:

PS C:\> .\mvnw spring-boot:run

We should now see this service in Consul, so let’s head back over to our browser, load up http://localhost:8500/ui/dc1/services (or refresh if you’re already there).

Distance Consul

Distance Service registered in Consul

As you can see from the above diagram, the distance service has been registered with consul.

We need to add the JTS library to the application classpath to aid us with the distance measurement:

file: distance/pom.xml

...
<dependency>
  <groupId>org.locationtech.jts</groupId>
  <artifactId>jts-core</artifactId>
  <version>1.15.1</version>
</dependency>
...

The distance microservice will serve one request /distance/start/@{start}/dest/@{dest} which returns the distance computed.

file: distance/src/main/java/com/juliuskrah/distance/DistanceApplication.java

@RestController
@SpringBootApplication
public class DistanceApplication {
  static GeometryFactory fact = new GeometryFactory();
  static WKTReader wktRdr = new WKTReader(fact);

  public static void main(String[] args) {
    SpringApplication.run(DistanceApplication.class, args);
  }
	
  @GetMapping(path = "/distance/start/@{start}/dest/@{dest}", produces = "application/json")
  public double points(@PathVariable String start, @PathVariable String dest) {
    double distance = 0.0;
    String[] pointA = start.split(",");
    String[] pointB = dest.split(",");
    String wktA = "POINT (" + pointA[0] + " " + pointA[1] +")";
    String wktB = "POINT (" + pointB[0] + " " + pointB[1] +")";
		
    try {
      Geometry A = wktRdr.read(wktA);
      Geometry B = wktRdr.read(wktB);

      System.out.println("Geometry A: " + A);
      System.out.println("Geometry B: " + B);
      DistanceOp distOp = new DistanceOp(A, B);
      distance = distOp.distance();
			
    } catch (ParseException e) {
      // ignore
    }	
    return distance;
  }	
}

Restart the distance service and test the endpoint http://localhost:57116/distance/start/@50.8307467,-1.2099742/dest/@5.5790564,-0.7073872, and you should see 45.25448120020473.

Our first microservice is open for business!

Points Microservice

Head over to Spring Intitializr to create the points microservice. Select Web and Consul Discovery, change “Artifact” to points then click Generate Project to download a zip file. Extract the contents of the zip file and load the project into your favorite IDE or text editor.

We will name the microservice points in bootstrap.yaml. We will use port 57216 for the points microservice:

file: points/src/main/resources/application.yaml

server:
  port: 57216
spring:
  cloud:
    consul:
      discovery:
        register-health-check: false

file: points/src/main/resources/bootstrap.yaml

spring:
  application:
    name: points

Give it a spin .\mvnw spring-boot:run to ensure everything is working.

If it’s all good we can implement the points microservice:

file: points/src/main/java/com/juliuskrah/point/PointsApplication.java

@RestController
@SpringBootApplication
public class PointsApplication {
  @Autowired
  private RestTemplate restTemplate;

  public static void main(String[] args) {
    SpringApplication.run(PointsApplication.class, args);
  }

  @GetMapping(path = "/points/start/@{start}/dest/@{dest}", produces = "application/json")
  public double points(@PathVariable String start, @PathVariable String dest) {
    return restTemplate.getForObject("http://distance/distance/start/@{start}/dest/@{dest}",
      double.class, start, dest);
  }

  @Bean
  @LoadBalanced
  public RestTemplate loadBalancedRestTemplate(RestTemplateBuilder builder) {
    return builder.build();
  }
}

A few things to note about the snippet above – @LoadBalanced, annotation to mark a RestTemplate bean to be configured to use a round-robin LoadBalancerClient for client-side load-balancing. This same annotation allows RestTemplate to determine the URI of the downstream microservice by name. This is how the http://DISTANCE/distance/start/@{start}/dest/@{dest} seemingly works despite missing a host and port in the URI passed to RestTemplate#getForObject.

This approach is efficient as we leave the job of discovery the services’ host and port to the discovery server (consul); we don’t have to worry about knowing the IPs of all microservices. In a large project consisting of thousands of microservices, you will soon come to agree that knowing all IPs of services starts to become a jarring task; this is where service discovery starts to shine.

Let’s put the points microservice to the test http://localhost:57216/points/start/@5.8307467,-1.2099742/dest/@5.5790564,-0.7073872.

This completes out points service using Spring-Boot.

Conclusion

In this tutorial we learned the fundamentals of Microservices. We learned what is a Discovery client, we also built two microservices to demonstrate how service discovery allows microservices to find each other.
As usual you can find the full example to this guide in the github repository. Until the next post, keep doing cool things :+1:.

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