Eureka Exercise

In this exercise, we will install and configure a Eureka server for service discovery, then alter all web services to lookup endpoints from Eureka rather than hard coding URLs.

Eureka Server

There is a simple Spring Boot starter that will stand up a Eureka server with almost no coding required. We’ll use the Spring initializer web site to create the server.

1. Navigate to https://start.spring.io
2. Create a Gradle project with Kotlin and the latest version of Spring Boot (2.2.0 at the time of writing)
3. Specify group: microservice.workshop
4. Specify artifact: eureka-server
5. For dependencies, add the following:
   • Eureka Server
6. Generate the project (causes a download)
7. Unzip the downloaded file somewhere convenient
8. Add the new project to your IDE workspace
   • Eclipse: File->Import->Existing Maven Project
   • IntelliJ: File->New->Module From Existing Sources…
   • VS Code: File->Add Folder to Workspace
9. Open microservice.workshop.eurekaserver.EurekaServerApplication.kt and add the @EnableEurekaServer annotation to the class
10. Navigate to src/main/resources, then rename application.properties to application.yml

11. Enter the following values in application.yml:

     info:
       app:
         name: Eureka Server
    
     server:
       port: 8761
    
     eureka:
       client:
         register-with-eureka: false
         fetch-registry: false
    

    These changes specify the port for the Eureka server (not really needed in this case because 8761 is default). More importantly, they tell the server not to register with Eureka - without these settings the server would try to register with itself!

12. Once these changes are made, start the server by starting the Spring boot application. After it starts, you can see the Eureka console at http://localhost:8761

Individual Web Services - Register with Eureka

The three individual web services (movie-service, movie-cast-service, and movie-award-service) need to register themselves with eureka when they start. This is very simple with Spring Boot - we simply have to add the eureka client dependency to the project and Spring Boot will do the magic. In the exercises, this has already been done, but eureka was disabled by a property.

In the application.yml for all three individual projects, change eureka.client.enabled to true, then start the three projects.

Once all three applications have been started then navigate to the eureka console at http://localhost:8761 - you should see all three services registered with eureka.

Note that you might see a scary looking warning in the Eureka console. You can safely ignore this warning.

Also note that the Eureka client will look for and register with a Eureka server at localhost:8761 by default. In production you would need to change this default by configuring a proper production grade Eureka server. See the “Spring Cloud Netflix” documentation for details.

Configure the REST Template Client Aggregator to Use Eureka

Our current services in the movie-aggregator-service-rt are configured with hard coded URLs for the target end points. We need to change them to use the DiscoveryClient.

In the application.yml for the aggregator project movie-aggregator-service-rt, change eureka.client.enabled to true.

Then for each of the three individual services:

1. Add private val discoveryClient: DiscoveryClient to the constructor parameters of the service

2. Lookup the service endpoint with code like the following:

        val url = discoveryClient.getInstances("movie-award-service")
                .firstOrNull()?.uri?.toString()
                ?: throw IllegalStateException("movie-award-service not available")
   

   Important Note:: you can find the proper service name by looking at the spring.application.name property in the application.yml file of each of the three remote services. That property sets the name of the application in the Eureka server.

3. Start the movie-aggregator-service-rt application. If you open the Eureka console, you will see that the aggregator service has also registered itself with eureka.
4. Start the traffic simulator and make sure that information is still being returned correctly from the aggregate service.

Once you are happy with the results, stop the movie-aggregator-service-rt - we’ll make more changes there for Hystrix in the next exercise.

Configure the Feign Client Aggregator to Use Eureka

Spring Feign and Eureka have a very simple integration - it’s automatic! Our current @FeignClient annotations are configured to fund services based on a hard coded URL. If we remove the URL from the annotation, the Feign client will attempt to lookup the service by name from a Eureka server.

1. Open application.yml in the movie-aggreagator-service project change the value of feign.hystrix.enabled to true
2. Open MovieAwardService and remove the url attribute from the @FeignClient annotation
3. Open MovieCastService and remove the url attribute from the @FeignClient annotation
4. Open MovieService and remove the url attribute from the @FeignClient annotation
5. Start the movie-aggregator-service application. If you open the Eureka console, you will see that the aggregator service has also registered itself with eureka.
6. Start the traffic-simulator and make sure that information is still being returned correctly from the aggregate service.

Once you are happy with the results, stop the movie-aggregator-service - we’ll make more changes there for Hystrix in the next exercise.