spring boot 2.0.3+spring cloud （Finchley）1、搭建服务注册和发现组件Eureka 以及构建高可用Eureka Server集群

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/

　　https://windmt.com/

案例代码地址：https://github.com/cralor7/springcloud