02.SpringCloud之Eureka

一.简介

RestTemplate 访问服务端时需要明确服务端地址，在服务端宕机、地址变化后则需要大量修改。微服务中使用注册中心对所有微服务管理，微服务启动后把自己注册到注册中心，注册中心以统一的方式暴露服务。

二.定义Eureka服务端

1.统一定义依赖模块

<groupId>com.vincent</groupId>
<artifactId>demo</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
      <module>eureka</module>
</modules>
<properties>
     <jdk.version>1.8</jdk.version>
      <spring-boot-dependencies.version>1.5.20.RELEASE</spring-boot-dependencies.version>
      <spring-cloud-dependencies.version>Edgware.RELEASE</spring-cloud-dependencies.version>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencyManagement>
	<dependencies>
    	<dependency>
        	<groupId>org.springframework.boot</groupId>
        	<artifactId>spring-boot-starter-parent</artifactId>
        	<version>${spring-boot-dependencies.version}</version>
	        <type>pom</type>
        	<scope>import</scope>
    	</dependency>
    	<dependency>
       		<groupId>org.springframework.cloud</groupId>
        	<artifactId>spring-cloud-dependencies</artifactId>
        	<version>${spring-cloud-dependencies.version}</version>
        	<type>pom</type>
        	<scope>import</scope>
    </dependency>
<dependencyManagement>

2.建立服务端模块

<parent>
      <artifactId>demo</artifactId>
      <groupId>com.vincent</groupId>
      <version>1.0-SNAPSHOT</version>
</parent>
<dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
</dependencies>

3.编写application.yml 配置文件

server:
  port: 7001
  context-path: /service-eureka

eureka:
  client:
    #eureka服务端本身也是一个微服务，设置微服务不向eureka注册中心注册服务
    register-with-eureka: false
    #设置当前的服务不需要从eureka注册中心获取服务注册信息
    fetch-registry: false
    #注册中心服务地址(不能乱写)，其注册中心服务地址为：schema://host-name:port/context-path/eureka,eureka是固定的注册中心访问映射
    service-url:
      defaultZone: http://localhost:7001/service-eureka/eureka
  server:
    eviction-interval-timer-in-ms: 60000 #设置对无用微服务清理时间间隔，默认是60s清理一次

当运行清理工作时将有如下输出：

2020-09-05 18:58:22.433  INFO 13108 --- [a-EvictionTimer] c.n.e.registry.AbstractInstanceRegistry  : Running the evict task with compensationTime 0ms

4.编写程序启动类并运行

package com.vincent;


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

@SpringBootApplication
@EnableEurekaServer
public class EureakApp {
    public static void main(String[] args) {
        SpringApplication.run(EureakApp.class,args);
    }
}

5.访问http://localhost:7001/service-eureka

在这里插入图片描述

三.注册微服务

1.引入Eureka客户端

<dependency>
   <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

2.修改application.yml 配置Eureka客户端

server:
  port: 8001
  context-path: /service-user
 
spring:
  application:
    name: service-user  #定义微服务名称


eureka:
  client:
    service-url:
      #注册中心地址，Eureka采用HA机制则使用","分割多个注册中心
      defaultZone: http://localhost:7001/service-eureka/eureka
  instance:
    #注册到注册中心的服务依靠心跳机制与Eureka保持联系，默认的心跳时间30s
    lease-renewal-interval-in-seconds: 30

3.编写启动类并启动

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package com.vincent;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

@SpringBootApplication
@EnableEurekaClient
public class ServiceApp {
    public static void main(String[] args) {
        SpringApplication.run(ServiceApp.class,args);
    }
}

4.http://localhost:7001/service-eureka
在这里插入图片描述
将能看到注册到注册中心的服务

四.Eureak HA 机制

Eureka 是微服务架构的核心，如果Eureka出现问题则所有服务都将瘫痪，可采用Eureka集群模式实现Eureka的高可用。集群模式需要让任意一台Eureka机器向其他Eureka机器注册。

1.Eureak 模块增加打包配置

<build>
  <plugins>
       <plugin>
           <groupId>org.springframework.boot</groupId>
           <artifactId>spring-boot-maven-plugin</artifactId>
           <configuration>
               <mainClass>com.vincent.EureakApp</mainClass>
           </configuration>
           <executions>
               <execution>
                   <goals>
                       <goal>repackage</goal>
                   </goals>
               </execution>
           </executions>
       </plugin>
   </plugins>
</build>

2.修改application.yml 配置文件

server:
  port: 7001
  context-path: /service-eureka

eureka:
  client:
    #eureka服务端本身也是一个微服务，设置微服务不向eureka注册中心注册服务
    register-with-eureka: false
    #设置当前的服务不需要从eureka注册中心获取服务注册信息
    fetch-registry: false
    #注册中心服务地址(不能乱写)，其注册中心服务地址为：schema://host-name:port/context-path/eureka,eureka是固定的注册中心访问映射
    service-url:
      #当前的eureka服务向其他的eureka主机注册
      defaultZone: http://localhost:7002/service-eureka/eureka,http://localhost:7003/service-eureka/eureka

3.新增配置文件application-7002.yml，application-7003.yml配置文件

server:
  port: 7002

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false
    service-url:
      defaultZone: http://localhost:7001/service-eureka/eureka,http://localhost:7003/service-eureka/eureka

server:
  port: 7003

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false
    service-url:
      defaultZone: http://localhost:7001/service-eureka/eureka,http://localhost:7002/service-eureka/eureka

3.打包并在终端分别运行：

java -jar target\eureka-1.0-SNAPSHOT.jar

java -jar target\eureka-1.0-SNAPSHOT.jar --spring.profiles.active=7002

java -jar target\eureka-1.0-SNAPSHOT.jar --spring.profiles.active=7003