Service Registration and Discovery , Spring cloud

What You Will Build

You will set up a Netflix Eureka service registry and then build a client that both registers itself with the registry and uses it to resolve its own host. A service registry is useful because it enables client-side load-balancing and decouples service providers from consumers without the need for DNS.

What You Need

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Starting with Spring Initializr.


To skip the basics, do the following:

Download and unzip the source repository for this guide, or clone it using Git: git clone https://github.com/spring-guides/gs-service-registration-and-discovery.git

cd into gs-service-registration-and-discovery/initial

Jump ahead to Start a Eureka Service Registry.

When you finish, you can check your results against the code in gs-service-registration-and-discovery/complete.

Starting with Spring Initializr

For all Spring applications, you should start with the 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 two applications. The first application (the service application) needs only the Eureka Server dependency. The following image shows the Initializr set up for the service application:

initializr service

The preceding image shows the Initializr with Maven chosen as the build tool. You can also use Gradle. It also shows values of com.example and service-registration-and-discovery-service as the Group and Artifact, respectively. You will use those values throughout the rest of this sample.

The following listing shows the pom.xml file (for the service application) that is created when you choose Maven:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.2.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>service-registration-and-discovery-service</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>service-registration-and-discovery-service</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Hoxton.SR1</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

	<repositories>
		<repository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
		</repository>
	</repositories>

</project>

The following listing shows the build.gradle file (for the service application) that is created when you choose Gradle:

plugins {
	id 'org.springframework.boot' version '2.2.2.RELEASE'
	id 'io.spring.dependency-management' version '1.0.8.RELEASE'
	id 'java'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
	maven { url 'https://repo.spring.io/milestone' }
}

ext {
	set('springCloudVersion', "Hoxton.SR1")
}

dependencies {
	implementation 'org.springframework.cloud:spring-cloud-starter-netflix-eureka-server'
	testImplementation('org.springframework.boot:spring-boot-starter-test') {
		exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
	}
}

dependencyManagement {
	imports {
		mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
	}
}

test {
	useJUnitPlatform()
}

The second application (the client application) needs the Eureka Server and Eureka Discovery Client dependencies. The following image shows the Initializr set up for the client application:

initializr client

The preceding image shows the Initializr with Maven chosen as the build tool. You can also use Gradle. It also shows values of com.example and service-registration-and-discovery-service as the Group and Artifact, respectively. You will use those values throughout the rest of this sample.

The following listing shows the pom.xml file (for the client application) that is created when you choose Maven:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.2.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.example</groupId>
	<artifactId>service-registration-and-discovery-client</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>service-registration-and-discovery-client</name>
	<description>Demo project for Spring Boot</description>

	<properties>
		<java.version>1.8</java.version>
		<spring-cloud.version>Hoxton.SR1</spring-cloud.version>
	</properties>

	<dependencies>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
		</dependency>
		<dependency>
			<groupId>org.springframework.cloud</groupId>
			<artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>org.springframework.cloud</groupId>
				<artifactId>spring-cloud-dependencies</artifactId>
				<version>${spring-cloud.version}</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

	<repositories>
		<repository>
			<id>spring-milestones</id>
			<name>Spring Milestones</name>
			<url>https://repo.spring.io/milestone</url>
		</repository>
	</repositories>

</project>

The following listing shows the build.gradle file (for the client application) that is created when you choose Gradle:

plugins {
	id 'org.springframework.boot' version '2.2.2.RELEASE'
	id 'io.spring.dependency-management' version '1.0.8.RELEASE'
	id 'java'
}

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
	maven { url 'https://repo.spring.io/milestone' }
}

ext {
	set('springCloudVersion', "Hoxton.SR1")
}

dependencies {
	implementation 'org.springframework.cloud:spring-cloud-starter-netflix-eureka-client'
	implementation 'org.springframework.cloud:spring-cloud-starter-netflix-eureka-server'
	testImplementation('org.springframework.boot:spring-boot-starter-test') {
		exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'
	}
}

dependencyManagement {
	imports {
		mavenBom "org.springframework.cloud:spring-cloud-dependencies:${springCloudVersion}"
	}
}

test {
	useJUnitPlatform()
}

For convenience, we have provided build files (a pom.xml file and a build.gradle file) at the top of the project (one directory above the service and client directories) that you can use to build both projects at once. We also added the Maven and Gradle wrappers there.

Start a Eureka Service Registry

You first need a Eureka Service registry. 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-service/src/main/java/com.example.serviceregistrationanddiscoveryservice/ServiceRegistrationAndDiscoveryServiceApplication.java) shows the service application:

package com.example.serviceregistrationanddiscoveryservice;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer
@SpringBootApplication
public class ServiceRegistrationAndDiscoveryServiceApplication {

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

When the registry starts, it will complain (with a stacktrace) that there are no replica nodes to which the registry can connect. In a production environment, you will want more than one instance of the registry. For our simple purposes, however, it suffices to disable the relevant logging.

By default, the registry also tries to register itself, so you need to disable that behavior as well.

It is a good convention to put this registry on a separate port when using it locally.

Add some properties to eureka-service/src/main/resources/application.properties to handle all of these requirements, as the following listing shows:

server.port=8761

eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false

logging.level.com.netflix.eureka=OFF
logging.level.com.netflix.discovery=OFF

Talking to the Registry

Now that you have started a service registry, you can stand up a client that both registers itself with the registry and uses the Spring Cloud DiscoveryClient abstraction to interrogate the registry for its own host and port. The @EnableDiscoveryClient activates the Netflix Eureka DiscoveryClient implementation. (There are other implementations for other service registries, such as Hashicorp’s Consul or Apache Zookeeper). The following listing (from eureka-client/src/main/java/example/serviceregistrationanddiscoveryclient/ServiceRegistrationAndDiscoveryClientApplication.java) shows the client application:

package com.example.serviceregistrationanddiscoveryclient;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@EnableDiscoveryClient
@SpringBootApplication
public class ServiceRegistrationAndDiscoveryClientApplication {

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

@RestController
class ServiceInstanceRestController {

	@Autowired
	private DiscoveryClient discoveryClient;

	@RequestMapping("/service-instances/{applicationName}")
	public List<ServiceInstance> serviceInstancesByApplicationName(
			@PathVariable String applicationName) {
		return this.discoveryClient.getInstances(applicationName);
	}
}

Whatever implementation you choose, you should soon see eureka-client registered under whatever name you specify in the spring.application.name property. This property is used a lot in Spring Cloud, often in the earliest phases of a service’s configuration. This property is used in service bootstrap and, so, by convention lives in eureka-client/src/main/resources/bootstrap.properties where it is found before src/main/resources/application.properties. The following listing shows the bootstrap.properties file:

spring.application.name=a-bootiful-client

The eureka-client defines a Spring MVC REST endpoint (ServiceInstanceRestController) that returns an enumeration of all the registered ServiceInstance instances at http://localhost:8080/service-instances/a-bootiful-client. See the Building a RESTful Web Service guide to learn more about building REST services with Spring MVC and Spring Boot.

Test the Application

Test the end-to-end result by starting the eureka-service first and then, once that has loaded, starting the eureka-client.

To run the Eureka service with Maven, run the following command in a terminal window (in the /complete directory):

./mvnw spring-boot:run -pl eureka-service

To run the Eureka client with Maven, run the following command in a terminal window (in the /complete directory):

./mvnw spring-boot:run -pl eureka-client

To run the Eureka service with Gradle, run the following command in a terminal window (in the /complete directory):

./gradlew :eureka-service:bootRun

To run the Eureka client with Gradle, run the following command in a terminal window (in the /complete directory):

./gradlew :eureka-client:bootRun

The eureka-client will take about a minute to register itself in the registry and to refresh its own list of registered instances from the registry. Visit the eureka-client in the browser, at http://localhost:8080/service-instances/a-bootiful-client. There, you should see the ServiceInstance for the eureka-client reflected in the response. If you see an empty <List> element, wait a bit and refresh the page.

Summary

Congratulations! You have just used Spring to stand up a Netflix Eureka service registry and to use that registry in a client application.

Post Views: 246
PinLinkedInPrint
Tagged:

Laisser un commentaire