服務註冊和發現

原文網址：https://spring.io/guides/gs/service-registration-and-discovery/

What you'll build

你將配置一個Eureka service註冊中心和一個client，client能自動註冊到註冊中心來解決埠問題。一個服務註冊中心非常有用，它使得client-side負載均衡，並從 consumers分離服務的providers而不需要DNS。

What you'll need

15分鐘

一個自己喜歡的編輯器或IDE

JDK1.8以上

Gradle 2.3+ 或者 Maven 3.0+

How to complete this guide

獲取原始碼

建立gradle工程，設定build.gradle

eureka-service/build.gradle

buildscript {
	ext {
		springBootVersion ='1.5.2.RELEASE'}
	repositories {
		mavenCentral()}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")}}

apply plugin:'java'
apply plugin:'eclipse'
 

apply plugin:'idea'
apply plugin:'org.springframework.boot'

jar {
	baseName ='eureka-service'
	version ='0.0.1-SNAPSHOT'}
sourceCompatibility =1.8
targetCompatibility =1.8

repositories {
	mavenCentral()}


dependencyManagement {
	imports {
		mavenBom 'org.springframework.cloud:spring-cloud-dependencies:Camden.SR5'
 
}}

dependencies {
	compile('org.springframework.cloud:spring-cloud-starter-eureka-server')
	testCompile('org.springframework.boot:spring-boot-starter-test')}


eclipse {
	classpath {
		 containers.remove('org.eclipse.jdt.launching.JRE_CONTAINER')
		 containers 'org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8'}}

buildscript {
	ext {
		springBootVersion ='1.5.2.RELEASE'}
	repositories {
		mavenCentral()}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")}}

apply plugin:'java'
apply plugin:'eclipse'
apply plugin:'idea'
apply plugin:'org.springframework.boot'

jar {
	baseName ='eureka-client'
	version ='0.0.1-SNAPSHOT'}
sourceCompatibility =1.8
targetCompatibility =1.8

repositories {
	mavenCentral()}

dependencyManagement {
	imports {
		mavenBom 'org.springframework.cloud:spring-cloud-dependencies:Camden.SR5'}}

dependencies {
	compile('org.springframework.cloud:spring-cloud-starter-eureka')
	compile('org.springframework.boot:spring-boot-starter-web')
	testCompile('org.springframework.boot:spring-boot-starter-test')
	testCompile('org.springframework.cloud:spring-cloud-starter-eureka-server')}

eclipse {
	classpath {
		 containers.remove('org.eclipse.jdt.launching.JRE_CONTAINER')
		 containers 'org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8'}}

• 它收集classpath中所有的jar包，並build一個獨立的，可執行的“uber-jar”，使得執行和傳遞服務更為方便
• 它尋找public static void main()方法來標記可執行的類
• 它提供一個嵌入的依賴解析器，設定版本號匹配Spring Boot依賴。你可以重寫成任意版本，但是他將預設為Boot的選擇版本集。

建立Maven工程

eureka-server/pom.xml

<?xml version="1.0" encoding="UTF-8"?><projectxmlns="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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.example</groupId><artifactId>eureka-service</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.2.RELEASE</version><relativePath/><!-- lookup parent from repository --></parent><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><java.version>1.8</java.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka-server</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><dependencyManagement><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>Camden.SR5</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></project>

eureka-client/pom.xml

<?xml version="1.0" encoding="UTF-8"?><projectxmlns="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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.example</groupId><artifactId>eureka-client</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.2.RELEASE</version><relativePath/><!-- lookup parent from repository --></parent><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><java.version>1.8</java.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka-server</artifactId><scope>test</scope></dependency></dependencies><dependencyManagement><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>Camden.SR5</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></project>

Spring Boot Maven plugin提高了許多方便的特性： 同上 gradle plugin

你首先需要一個Eureka Service註冊中心，你可以使用Spring Cloud的@EnableEurekaServer來建立註冊中心，以便其他應用訪問。這是一個普通的Spring Boot應用，加上註解來提供服務註冊功能。

service中建立一個application.java

package hello;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;@EnableEurekaServer@SpringBootApplicationpublicclassEurekaServiceApplication{publicstaticvoid main(String[] args){SpringApplication.run(EurekaServiceApplication.class, args);}}

當註冊中心啟動時，會發生錯誤，帶有堆疊資訊：“沒有註冊中心可連線的副本節點”。在生產環境下，你想要註冊中心不止一個例項，然而，出於簡單的目的，它足以使相關日誌失效。

預設情況下，註冊中心也將試圖將自己也註冊上，所以你也需要禁止它註冊。

一般在本地使用時，協定將註冊中心放在一個單獨的埠上。

新增一些屬性來處理這些要求：

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

現在我們已經搭建好註冊中心了，現在搭建一個客戶端，讓它在註冊中心自己註冊，並且使用Spring Cloud DiscoveryClient抽象去註冊中心詢問主機和埠。@EnableDiscoveryClient啟用Netflix Eureka DiscoveryClient實現。還有其他實現用於其他服務註冊中心，如Hashicorp’s Consul or Apache Zookeeper.

client中建立application.java

package hello;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@SpringBootApplicationpublicclassEurekaClientApplication{publicstaticvoid main(String[] args){SpringApplication.run(EurekaClientApplication.class, args);}}@RestControllerclassServiceInstanceRestController{@AutowiredprivateDiscoveryClient discoveryClient;@RequestMapping("/service-instances/{applicationName}")publicList<ServiceInstance> serviceInstancesByApplicationName(@PathVariableString applicationName){returnthis.discoveryClient.getInstances(applicationName);}}

eureka-client/src/main/resources/bootstrap.properties

spring.application.name=a-bootiful-client

eureka-client定義一個Spring MVC REST端點，ServiceInstanceRestController，它將返回一個列舉，其中包含了註冊中心在http://localhost:8080/service-instances/a-bootiful-client註冊的所有ServiceInstance例項。查閱Building a RESTful Web Service指導來學習更多關於用Spring MVC 和 Spring Boot建立REST服務。

測試end-to-end(端對端)結果，首先啟動eureka-service，載入完畢後，啟動eureka-client，客戶端將花一分鐘將它註冊到註冊中心，並從註冊中心重新整理它自己已註冊是例項列表。所有的這些閾值都是可配置的，在瀏覽器中訪問客戶端http://localhost:8080/service-instances/a-bootiful-client。你將看到客戶端的ServiceInstance對映在響應中。

遇到的問題：

1. 客戶端註冊不成功，找不到server，解決辦法：在bootstrap.properties中配置server地址：eureka.client.serviceUrl.defaultZone=http://localhost:8761/eureka/