:toc: :icons: font :source-highlighter: prettify :project_id: gs-service-registration-and-discovery :java_version: 17
This guide walks you through the process of starting and using the Netflix Eureka service registry.
== What You Will Build
You will set up a https://github.com/spring-cloud/spring-cloud-netflix[Netflix Eureka service registry^], named eureka-server, and then build two web clients, named servicea and serviceb, that both register with the Eureka server.
One of the web clients, serviceb, will call the other web client, servicea, using org.springframework.cloud.client.discovery.DiscoveryClient and https://docs.spring.io/spring-framework/reference/integration/rest-clients.html#rest-restclient[Spring Framework's Rest Client^].
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[[scratch]] == Starting with Spring Initializr
For all Spring applications, you should start with the https://start.spring.io[Spring Initializr^]. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the set up for you.
This guide needs three applications. The first application (the server application) needs only the Eureka Server dependency. The second and third applications (the client applications) need the Eureka Discovery Client and Spring Web dependencies.
:server-link: https://start.spring.io/#!type=maven-project&language=java&packaging=jar&groupId=com.example&artifactId=eureka-server&name=eureka-server&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.eureka-server&dependencies=cloud-eureka-server :clienta-link: https://start.spring.io/#!type=maven-project&language=java&packaging=jar&groupId=com.example&artifactId=servicea&name=servicea&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.servicea&dependencies=cloud-eureka,web :clientb-link: https://start.spring.io/#!type=maven-project&language=java&packaging=jar&groupId=com.example&artifactId=serviceb&name=serviceb&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.serviceb&dependencies=cloud-eureka,web
You can use the following links for pre-initialized projects from Spring Initializr:
NOTE: Due to the number of services in this guide, only the solutions are provided in the GitHub repository. To start from scratch, generate the blank projects using the links above or using https://start.spring.io[Spring Initializr], as defined below.
To manually initialize the Eureka Server project:
. Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you. . Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Maven and Java. . Click Dependencies and select Eureka Server for the server application. . Click Generate. . Download the resulting ZIP file, which is an archive of a web application that is configured with your choices.
To manually initialize the Service A and Service B projects:
. Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you. . Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Maven and Java. . Select Eureka Discovery Client and Spring Web for the client applications. . Click Generate. . Download the resulting ZIP file, which is an archive of a web application that is configured with your choices.
NOTE: If your IDE has the Spring Initializr integration, you can complete this process from your IDE.
[[initial]] == Start a Eureka Service Registry
You first need a Eureka Server. You can use Spring Cloud's @EnableEurekaServer
to stand up a registry with which other applications can communicate. This is a regular
Spring Boot application with one annotation (@EnableEurekaServer) added to enable the
service registry. The following listing (from
eureka-server/src/main/java/com/example/eurekaserver/EurekaServerApplication.java)
shows the server application:
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In a production environment, you likely want more than one instance of the registry. You can find additional information about configuring the Eureka Server https://docs.spring.io/spring-cloud-netflix/reference/spring-cloud-netflix.html#spring-cloud-eureka-server[here^].
By default, the registry also tries to register itself, so you need to disable that behavior. Additionally, it is a good convention to put this registry on a separate port when using it locally.
Add some properties to eureka-server/src/main/resources/application.yml to
handle these requirements, as the following listing shows:
====
You can now start the Eureka server by running ./mvnw spring-boot:run.
== Talking to the Registry
Now that you have started a service registry, you can stand up clients that interact with the registry. Our client applications, ServiceA and ServiceB, automatically register with the Eureka server because we have spring-cloud-starter-netflix-eureka-client on the classpath.
To avoid port conflicts, set the server.port parameter in both ServiceA and ServiceB:
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====
At this point you, should be able to run all three applications.
You can use the IDE or execute the ./mvnw spring-boot:run command from each application folder.
When the applications run, you can view the http://localhost:8761/[Eureka dashboard^].
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== Service A Endpoint
Create a new class called com/example/servicea/controller/ServiceARestController.java in the servicea project to expose an endpoint you can use to test the application.
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== Service B Endpoint
Create a new class called com/example/serviceb/controller/ServiceBRestController.java in the serviceb project to expose an endpoint that calls servicea.
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This class uses a DiscoveryClient to find the serviceId of servicea based only on the application name.
This guide has only one instance of servicea, so we can look only at the first instance.
This is seen in the following line:
ServiceInstance serviceInstance = discoveryClient.getInstances("servicea").get(0);Once you have a ServiceInstance that refers to the location of servicea, you can now use the information in Spring Framework's https://docs.spring.io/spring-framework/reference/integration/rest-clients.html#rest-restclient[Rest Client].
... = restClient.get().uri(serviceInstance.getUri() + "/helloWorld")...
You can test all three applications by running the following command:
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And you should see the result:
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== Test the Application
This guide walked through the following steps (which you could do by implementing the code shown throughout this guide or by using the code in the solution repository):
eureka-server with the ./mvnw spring-boot:run command from the eureka-server folderservicea with the ./mvnw spring-boot:run command from the servicea folderserviceb with the ./mvnw spring-boot:run command from the serviceb folderservicea and serviceb are registered by viewing the Eureka Dahsboard at http://localhost:8761/curl http://localhost:8082/helloEureka command to test all three applications are working properlyHello world from Service A!NOTE: There is a short delay while servicea and serviceb register themselves and refresh the instances from the registry. If the curl command initially fails, wait a minute and try again.
== Summary Congratulations! You have just used Spring to stand up a Netflix Eureka service registry and to use that registry in a client application.
== See Also
The following guides may also be helpful:
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