原文：https://xsxy007.github.io/2019/10/SpringCloud-Eureka/Eureka 是Netflix开源的一款提供服务注册和发现的产品，提供了完整的Service Registery和Service Discovery实现，也是SpringCloud体系中最核心的组件之一
Eureka
由上边的图可以看出，Eureka由客户端和服务端组成，服务用用于服务的注册服务器，客户端用作服务的提供者和发现者
案例
git@github.com:xsxy007/springcloud-demo.git
Eureka Server
springboot 已经很好的支持了Eureka，只需要在pom中加入Eureka依赖，并在Application启动类中加上相关注解即可
1、pom依赖添加
本次使用的springboot版本为2.1.9；springcloud版本为Greenwich.RELEASE
以下列出了所有的依赖（ps：一开始因为springcloud和springboot的版本依赖问题，导致项目一直启动报错）
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
<spring-cloud.version>Greenwich.RELEASE</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>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>${spring-cloud.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
2、在启动类上加注解@EnableEurekaServer注解
@SpringBootApplication
@EnableEurekaServer
public class SpringcloudDemoApplication {
public static void main(String[] args) {
SpringApplication.run(SpringcloudDemoApplication.class, args);
}
}
3、配置文件
在默认配置下，该注册中心会将自己作为客户端尝试注册自己，因此在单机的注册中心时，需要将此机制关闭掉
server:
port: 8761 # 使用的是默认的端口
spring:
application:
name: eureka-server
eureka:
client:
register-with-eureka: false
fetch-registry: false
service-url:
defaultZone: http://localhost:${server.port}/eureka/
eureka.client.register-with-eureka：表示是否将自己注册的eureka server，默认为trueeureka.client.fetch-registry：表示是否从eureka server上拉取注册信息，默认为trueeureka.client.service-url.defaultZone：表示注册中心的地址（默认为localhost:8761/eureka/）
4、启动项目
启动项目后访问localhost:8761 即可显示如下页面，此时 Instances current Registers里边并没有内容
集群配置
简单的集群，只要将各个注册中心相互配置即可eureka.client.serviceUrl.defaultZone=http://域名:/${server.port}/eureka/,http://域名:/${server.port}/eureka/ 请其他注册中心的地址配置的defaultZone中
源码分析
从启动类注解开始 @EnableEurekaServer
可以注意注释中的EurekaServerAutoConfiguration，该类就是EurekaServer的自动配置类
/**
* Annotation to activate Eureka Server related configuration {@link EurekaServerAutoConfiguration}
* @author Dave Syer
* @author Biju Kunjummen
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EurekaServerMarkerConfiguration.class)
public @interface EnableEurekaServer {
}
再看上边注解类上有一个 @Import(EurekaServerMarkerConfiguration.class)，进入该类查看
// 可以看到，该类并没有什么实现，该类的作用：是为了控制 `EurekaServerAutoConfiguration` 类是否加载
@Configuration
public class EurekaServerMarkerConfiguration {
@Bean
public Marker eurekaServerMarkerBean() {
return new Marker();
}
class Marker {
}
}
查看 EurekaServerAutoConfiguration（该类是在通过Springboot的@EnableAutoconfiguration 来加载spring.factories中的类的）
// 省略了部分代码
@Configuration
@Import(EurekaServerInitializerConfiguration.class)
@ConditionalOnBean(EurekaServerMarkerConfiguration.Marker.class) // 当存在 EurekaServerMarkerConfiguration 类是才初始化当前文件
@EnableConfigurationProperties({ EurekaDashboardProperties.class,
InstanceRegistryProperties.class })
@PropertySource("classpath:/eureka/server.properties")
public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
// 实例化一个配置类，该配置类在 EurekaServerInitializerConfiguration 中会使用到
@Configuration
protected static class EurekaServerConfigBeanConfiguration {
@Bean
@ConditionalOnMissingBean
public EurekaServerConfig eurekaServerConfig(EurekaClientConfig clientConfig) {
EurekaServerConfigBean server = new EurekaServerConfigBean();
if (clientConfig.shouldRegisterWithEureka()) {
// Set a sensible default if we are supposed to replicate
server.setRegistrySyncRetries(5);
}
return server;
}
}
// eurekaServer的上下文
@Bean
public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {
return new DefaultEurekaServerContext(this.eurekaServerConfig, serverCodecs,
registry, peerEurekaNodes, this.applicationInfoManager);
}
// eurekaServer的启动
@Bean
public EurekaServerBootstrap eurekaServerBootstrap(PeerAwareInstanceRegistry registry,
EurekaServerContext serverContext) {
return new EurekaServerBootstrap(this.applicationInfoManager,
this.eurekaClientConfig, this.eurekaServerConfig, registry,
serverContext);
}
}
注意 EurekaServerInitializerConfiguration 类，该类实现了lifecycle接口，所以会被spring容器毁掉start方法
@Override
public void start() {
new Thread(new Runnable() {
@Override
public void run() {
try {
//TODO: is this class even needed now?
eurekaServerBootstrap.contextInitialized(
EurekaServerInitializerConfiguration.this.servletContext);
log.info("Started Eureka Server");
publish(new EurekaRegistryAvailableEvent(getEurekaServerConfig()));
EurekaServerInitializerConfiguration.this.running = true;
publish(new EurekaServerStartedEvent(getEurekaServerConfig()));
}
catch (Exception ex) {
// Help!
log.error("Could not initialize Eureka servlet context", ex);
}
}
}).start(); // 调用 start 方法启动线程
}
参考： https://blog.csdn.net/cuixhao110/article/details/88353714
