一 、搭建Eureka
编写Eureka Server
由于有多个spring boot项目，采用maven多module的结构，项目结构如下：
新建一个maven主工程，在主maven的pom文件中引入spring boot和spring cloud的依赖
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion> <groupId>com.cralor</groupId>
<artifactId>chap5-2-eureka</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging> <parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.3.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent> <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>Finchley.RELEASE</spring-cloud.version>
</properties> <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> <!--使用aliyun镜像-->
<repositories>
<repository>
<id>alimaven</id>
<name>Maven Aliyun Mirror</name>
<url>http://maven.aliyun.com/nexus/content/repositories/central/</url>
<releases>
<enabled>true</enabled>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories> </project>
采用spring initializr 方式新建module工程eureka-server，作为服务注册中心。在pom文件中引入相关依赖包括继承主maven工程的pom文件，eureka server的起步依赖spring-cloud-starter-netflix-eureka-server
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion> <groupId>com.cralor</groupId>
<artifactId>eureka-server</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging> <name>eureka-server</name>
<description>Demo project for Spring Boot</description> <parent>
<groupId>com.cralor</groupId>
<artifactId>chap5-2-eureka</artifactId>
<version>0.0.1-SNAPSHOT</version>
<relativePath/> <!-- lookup parent from repository -->
</parent> <properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.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> <build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build> </project>
在配置文件application.yml中做相关配置，指定eureka server 的端口号为8761，默认eureka server会向自己注册，需要配置eureka.client.registerWithEureka和eureka.client.fetchRegistry为false，防止自己注册自己。
server:
port: 8761
eureka:
instance:
hostname: localhost
client:
register-with-eureka: false
fetch-registry: false
serviceUrl:
defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/
在工程启动类加上注解@EnableEurekaServer，开启eureka server功能
@EnableEurekaServer
@SpringBootApplication
public class EurekaServerApplication { public static void main(String[] args) {
SpringApplication.run(EurekaServerApplication.class, args);
}
}
启动程序，在浏览器访问eureka server 主界面http://localhost:8761，在上面的Instance currently registered with Eureka这一项还没有注册任何实例，因为还没有eureka client 客户端向注册中心注册服务。
编写Eureka Client
新建module工程eureka-client，该工程作为Eureka Client的工程会向服务注册中心Eureka Server注册。在pom文件引入相关依赖包括eureka client起步依赖spring-cloud-starter-netflix-eureka-client
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion> <groupId>com.cralor</groupId>
<artifactId>eureka-client</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging> <name>eureka-client</name>
<description>Demo project for Spring Boot</description> <parent>
<groupId>com.cralor</groupId>
<artifactId>chap5-2-eureka</artifactId>
<version>0.0.1-SNAPSHOT</version>
<relativePath/> <!-- lookup parent from repository -->
</parent> <properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties> <dependencies>
<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>
<scope>test</scope>
</dependency> <dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>
</dependencies> <build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build> </project>
在配置文件中做相关配置，程序名为eureka-client，端口号8762，服务注册地址为http://localhost:8761/eureka/。
server:
port: 8762
spring:
application:
name: eureka-client
eureka:
client:
serviceUrl:
defaultZone: http://localhost:8761/eureka/
启动类保持默认生成的即可， Finchley 这个版本的 Spring Cloud 已经无需添加@EnableDiscoveryClient注解了。（那么如果我引入了相关的 jar 包又想禁用服务注册与发现怎么办？设置eureka.client.enabled=false）
@EnableDiscoveryClient is no longer required. You can put a DiscoveryClient implementation on the classpath to cause the Spring Boot application to register with the service discovery server.
Spring Cloud - @EnableDiscoveryClient
@SpringBootApplication
public class EurekaClientApplication { public static void main(String[] args) {
SpringApplication.run(EurekaClientApplication.class, args);
}
}
启动eureka client工程，成功后会在控制台打印
:DiscoveryClient_EUREKA-CLIENT/DESKTOP-R9RM7VT:eureka-client:8762: registering service...
DiscoveryClient_EUREKA-CLIENT/DESKTOP-R9RM7VT:eureka-client:8762 - registration status: 204
说明eureka client已向eureka server注册了，访问http://localhost:8761，显示已有一个实例注册
二、构建高可用Eureka Server集群
1、在实际项目中，一个注册中心远远无法满足实际的生产环境，我们需要多个注册中心进行集群，达到真正的高可用。
首先更改eureka-server的配置文件application.yml，采用多配置文件格式，在启动时指定具体的配置文件
spring:
profiles:
active: native
application:
name: peer-cluster
application-peer1.yml
server:
port: 8761
eureka:
instance:
hostname: peer1
client:
serviceUrl:
defaultZone: http://peer2:8762/eureka/
application-peer2.yml
server:
port: 8762
eureka:
instance:
hostname: peer2
client:
serviceUrl:
defaultZone: http://peer1:8761/eureka/
定义了两个配置文件peer1和peer2，hostname分别是peer1和peer2，并且在application.yml定义了相同的实例名称peer-cluster。peer1的注册地址为http://peer2:8762/eureka/，peer2的注册地址为http://peer1:8761/eureka/，让它们互相注册，以达到同步的目的。
因为是在本地搭建eureka server集群，需要修改本地的host。Windows在C:\Windows\System32\drivers\etc\hosts中修改，mac电脑通过终端vim/etc/hosts进行编辑修改，修改如下：
127.0.0.1 peer1 127.0.0.1 peer2
使用maven的package命令生成eureka server的jar包，在target目录下会生成eureka-server-0.0.1-SNAPSHOT.jar。通过java -jar的方式分别启动peer1和peer2，命令如下：
java -jar eureka-server-0.0.1-SNAPSHOT.jar --spring.profiles.active=peer1
java -jar eureka-server-0.0.1-SNAPSHOT.jar --spring.profiles.active=peer2
访问http://peer1:8761和http://peer2:8762如图
可以看到peer1和peer2分别为对方的实例并且registered-replicas和available-replicas分别有了对方的地址
2、修改eureka-client的配置文件
server:
port: 8763
spring:
application:
name: eureka-client
eureka:
client:
serviceUrl:
defaultZone: http://peer1:8761/eureka
此时eureka-client的配置文件并没有指定向peer2的节点eureka server注册，访问peer2主界面http://peer2:8762/eureka。节点peer2的主界面显示eureka client已向peer2注册，可见peer1的注册信息列表已经同步到了peer2节点，这是因为eureka是通过在各个节点进行复制来达到高可用的目的。
ps：关于spring cloud组件的这几篇随笔文章是在我学习方志朋老师的《深入理解Spring Cloud与微服务构建》一书的过程中写的。微信号：walkingstory。
写的非常好的文章：https://windmt.com/2018/04/14/spring-cloud-1-services-governance/
案例代码地址：https://github.com/cralor7/springcloud
