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SpringCloud服务注册中心双节点集群(Eureka集群)

作者：xcbeyond
疯狂源自梦想，技术成就辉煌！微信公众号：《程序猿技术大咖》号主，专注后端开发多年，拥有丰富的研发经验，乐于技术输出、分享，现阶段从事微服务架构项目的研发工作，涉及架构设计、技术选型、业务研发等工作。对于Java、微服务、数据库、Docker有深入了解，并有大量的调优经验。

0、前言
最近在进行重构一个新项目，为了后续更好的落地，适应于日新月异的技术更新，进行了各方的技术选型及技术预研，最终选型基于微服务架构体系进行开发重构。项目构建前最重要的一步就是要想清楚，整体的部署架构、高可用性(HA)等等，做好前期的部署架构技术调研，确定最终方案。

在微服务架构体系中，核心技术便是Spring Cloud，通过登录官网查看SpringCloud已经集成了好多优质的项目，供我们使用借鉴。而SpringCloud Eureka是云端服务发现，一个基于 REST 的服务，用于定位服务，以实现云端中间层服务发现和故障转移，并且支持集群部署。因此，本次部署架构技术方案选型打算采用Eureka集群。

(关于Eureka服务注册与发现请查看上一章节内容【SpringCloud系列】一、SpringCloud服务注册与发现(Eureka))

本文将阐述SpringCloud服务注册中心双节点集群(Eureka集群)方案及集群demo。

1、Eureka集群概述
1.1 基本原理

如上图，是Eureka集群配置图。

- 不同节点的Eureka Server通过Replicate(复制)进行数据同步
- Application Service为服务提供者
- Application Client为服务消费者
- Make Remote Call完成一次服务调用

服务启动后向Eureka注册，Eureka Server会将注册信息向其他Eureka Server进行同步，当服务消费者要调用服务提供者，则向服务注册中心获取服务提供者地址(即：服务应用名，spring.application.name参数配置)，然后会将服务提供者地址缓存在本地，下次再调用时，则直接从本地缓存中取，完成一次调用。

当服务注册中心Eureka Server检测到服务提供者因为宕机、网络原因不可用时，则在服务注册中心将服务置为DOWN状态，并把当前服务提供者状态向订阅者发布，订阅过的服务消费者更新本地缓存。

服务提供者在启动后，周期性（默认30秒）向Eureka Server发送心跳，以证明当前服务是可用状态。Eureka Server在一定的时间（默认90秒）未收到客户端的心跳，则认为服务宕机，注销该实例。

1.2 Eureka自我保护机制
在默认配置中，Eureka Server在默认90s没有得到客户端的心跳，则注销该实例，但是往往因为微服务跨进程调用，网络通信往往会面临着各种问题，比如微服务状态正常，但是因为网络分区故障时，Eureka Server注销服务实例则会让大部分微服务不可用，这很危险，因为服务明明没有问题。

为了解决这个问题，Eureka 有自我保护机制，通过在Eureka Server配置如下参数，可启动保护机制。

eureka.server.enable-self-preservation=true
它的原理是，当Eureka Server节点在短时间内丢失过多的客户端时（可能发送了网络故障），那么这个节点将进入自我保护模式，不再注销任何微服务，当网络故障回复后，该节点会自动退出自我保护模式。

1.3 Eureka高可用集群
理论上来讲，因为服务消费者本地缓存了服务提供者的地址，即使Eureka Server宕机，也不会影响服务之间的调用，但是一旦新服务上线，已经在缓存在本地的服务提供者不可用了，服务消费者也无法知道，所以保证Eureka Server的高可用还是很有必要的。

在分布式系统中，任何的地方存在单点，整个体系就不是高可用的，Eureka 也一样，在上面的架构图中Eureka Server不是以单点存在的，而是以集群的方式对外提供服务。

2、Eureka双中心节点集群
本节以具体示例说明Eureka集群及配置。

2.1 创建Eureka Server
（1）新建springCloudEurekaCluster项目作为Eureka Server集群项目：

pom.xml如下：

<?xml version="1.0"?>
<project
   xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"
   xmlns="http://maven.apache.org/POM/4.0.0"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   <modelVersion>4.0.0</modelVersion>

   <groupId>com.xcbeyond.springcloud</groupId>
   <artifactId>springCloudEurekaCluster</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <name>springCloudEurekaCluster</name>
   <url>http://maven.apache.org</url>

   <parent>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-parent</artifactId>
       <version>2.0.0.RELEASE</version>
       <relativePath/>
   </parent>

   <properties>
       <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>

   <dependencies>
       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter</artifactId>
       </dependency>

       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-web</artifactId>
       </dependency>

       <dependency>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-starter-test</artifactId>
       </dependency>

       <dependency>
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
           <version>2.0.0.RELEASE</version>
       </dependency>
       <dependency>
           <groupId>org.springframework.cloud</groupId>
           <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
           <version>2.0.0.RELEASE</version>
       </dependency>
   </dependencies>

   <description>Eureka集群</description>
</project>
（2）配置application.properties。

在Eureka Server集群时，需要部署多个节点，则需要同一个项目，使用不同的配置。因此，在本例中使用springCloudEurekaCluster一个项目通过不同的启动参数来启动占用不同端口的两个Server服务，来模拟Eureka集群。则使用下面三个*.properties配置文件：

application.properties
application-eureka-server1.properties
application-eureka-server2.properties
application.properties

#应用名
spring.application.name=eureka-cluster
application-eureka-server1.properties

##eureka-server1节点配置，配置参数--spring.profiles.active=eureka-server1来启动该环境
spring.profiles=eureka-server1
server.port=8761
eureka.instance.hostname=eureka-server1
eureka.client.serviceUrl.defaultZone=http://eureka-server2:8762/eureka/
application-eureka-server2.properties

##eureka-server2节点配置，配置参数--spring.profiles.active=eureka-server2来启动该环境
spring.profiles=eureka-server2
server.port=8762
eureka.instance.hostname=eureka-server2
eureka.client.serviceUrl.defaultZone=http://eureka-server1:8761/eureka/
application-eureka-server1.properties、application-eureka-server2.properties配置文件设置了不同的端口(server.port)，重点是参数eureka.client.serviceUrl.defaultZone，分别配置对方的地址作为Eureka Client进行相互注册。由于采用了参数配置eureka.instance.hostname及http://eureka-server1的写法，则需要在进行hosts的配置，window在C:\Windows\System32\drivers\etc\hosts，Linux是在/etc/host，此处，以我windows本机说明，在hosts文件中最近如下配置：

127.0.0.1 eureka-server1
127.0.0.1 eureka-server2
（3）新建启动类。

com.xcbeyond.springcloud.eurekacluster.EurekaClusterApplication.java

package com.xcbeyond.springcloud.eurekacluster;

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

/**
* Eureka集群启动类
* @author xcbeyond
* 2018年8月7日上午10:34:01
*/
@SpringBootApplication
//开启对EurekaServer的支持，即：作为Eureka服务端
@EnableEurekaServer
//开启作为Eureka Server的客户端的支持
@EnableDiscoveryClient
public class EurekaClusterApplication {
   public static void main(String[] args) {
       SpringApplication.run(EurekaClusterApplication.class, args);
   }
}
重点添加@EnableEurekaServer注解，开启对EurekaServer的支持，即：作为Eureka服务端。

项目源码：https://download.csdn.net/download/xcbeyond/10592831

2.2.Eureka集群启动及验证
2.2.1 集群启动
在创建Eureka server项目时，创建了两个properties配置文件，作为集群不同的节点配置文件，在启动项目时，只需指定启动参数--spring.profiles.active=eureka-server1来指定对应配置环境，运行启动类即可。Eclipse IDE开发环境下，配置启动参数方式如下：

在启动第一个节点eureka-server1过程中，会持续出现如下错误信息：

2018-08-09 10:29:25.225 ERROR 7964 --- [nfoReplicator-0] c.n.d.s.t.d.RedirectingEurekaHttpClient : Request execution error

com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused: connect
   at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
   at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123) ~[jersey-client-1.19.1.jar:1.19.1]
   at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.sun.jersey.api.client.Client.handle(Client.java:652) ~[jersey-client-1.19.1.jar:1.19.1]
   at com.sun.jersey.api.client.WebResource.handle(WebResource.java:682) ~[jersey-client-1.19.1.jar:1.19.1]
   at com.sun.jersey.api.client.WebResource.access$200(WebResource.java:74) ~[jersey-client-1.19.1.jar:1.19.1]
   at com.sun.jersey.api.client.WebResource$Builder.post(WebResource.java:570) ~[jersey-client-1.19.1.jar:1.19.1]
   at com.netflix.discovery.shared.transport.jersey.AbstractJerseyEurekaHttpClient.register(AbstractJerseyEurekaHttpClient.java:56) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.MetricsCollectingEurekaHttpClient.execute(MetricsCollectingEurekaHttpClient.java:73) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.executeOnNewServer(RedirectingEurekaHttpClient.java:118) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.RedirectingEurekaHttpClient.execute(RedirectingEurekaHttpClient.java:79) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:120) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.2.jar:1.9.2]
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_121]
   at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
   at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]
Caused by: java.net.ConnectException: Connection refused: connect
   at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method) ~[na:1.8.0_121]
   at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85) ~[na:1.8.0_121]
   at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350) ~[na:1.8.0_121]
   at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206) ~[na:1.8.0_121]
   at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188) ~[na:1.8.0_121]
   at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172) ~[na:1.8.0_121]
   at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) ~[na:1.8.0_121]
   at java.net.Socket.connect(Socket.java:589) ~[na:1.8.0_121]
   at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:121) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:180) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:144) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:134) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:610) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:445) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.client.AbstractHttpClient.doExecute(AbstractHttpClient.java:835) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:118) ~[httpclient-4.5.5.jar:4.5.5]
   at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56) ~[httpclient-4.5.5.jar:4.5.5]
   at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:173) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
   ... 30 common frames omitted

2018-08-09 10:29:25.225 WARN 7964 --- [nfoReplicator-0] c.n.d.s.t.d.RetryableEurekaHttpClient : Request execution failed with message: java.net.ConnectException: Connection refused: connect
2018-08-09 10:29:25.225 WARN 7964 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient : DiscoveryClient_EUREKA-CLUSTER/xuchao:eureka-cluster:8761 - registration failed Cannot execute request on any known server

com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
   at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) [eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.2.jar:1.9.2]
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_121]
   at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
   at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]

2018-08-09 10:29:25.225 WARN 7964 --- [nfoReplicator-0] c.n.discovery.InstanceInfoReplicator : There was a problem with the instance info replicator

com.netflix.discovery.shared.transport.TransportException: Cannot execute request on any known server
   at com.netflix.discovery.shared.transport.decorator.RetryableEurekaHttpClient.execute(RetryableEurekaHttpClient.java:112) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator$1.execute(EurekaHttpClientDecorator.java:59) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.SessionedEurekaHttpClient.execute(SessionedEurekaHttpClient.java:77) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.shared.transport.decorator.EurekaHttpClientDecorator.register(EurekaHttpClientDecorator.java:56) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:829) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator.run(InstanceInfoReplicator.java:121) ~[eureka-client-1.9.2.jar:1.9.2]
   at com.netflix.discovery.InstanceInfoReplicator$1.run(InstanceInfoReplicator.java:101) [eureka-client-1.9.2.jar:1.9.2]
   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_121]
   at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_121]
   at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_121]
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_121]
   at java.lang.Thread.run(Thread.java:745) [na:1.8.0_121]
     分析日志可知，是在第一个节点eureka-server1启动后，向eureka-server2注册时连接拒绝(java.net.ConnectException: Connection refused: connect)导致，因为此时eureka-server2节点还未启动，所有出现此类错误信息是正常的，eureka-server2启动后，此类错误日志将不会出现。关于各类集群环境不同节点在顺次启动时都会出现类似错误信息的，大家不必惊慌！

在浏览器中分别访问各自节点的地址、端口，http://eureka-server1:8761/、http://eureka-server2:8762/

从上面两张图可以看出，DS Replicas、registered-replicas、available-replicas分别有了对方的地址，即：相互Replicate、相互注册，则说明Eureka集群成功。

2.2高可用性验证
如果出现其中一个节点宕机，结果将会如何呢？

停掉eureka-server1服务作为模拟宕机，访问http://eureka-server1:8761/显示无法访问，http://eureka-server2:8762/正常访问，eureka-server2节点信息如下：

发生变化之处，如上图标注，eureka-server1宕机后，eureka-server2依旧可以发现eureka-server1，而eureka-server1只是变为unavailable-replicas而已，最终不会影响其他客户端的注册。当eureka-server1启动后，一切自动恢复。

（其他高可用性的验证，感兴趣的可一一验证）

框架