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服务治理Spring Cloud Eureka

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本文字数： 19k 阅读时长 ≈ 17 mins.

2018年7月，官方宣布Eureka 2.x停止开源计划了。

详细请看：
http://github.com/Netflix/eureka/wiki

尴尬了。

介绍

Eureka是Spring Cloud中的一个负责服务注册与发现的组件。遵循着CAP理论中的A（可用性）、P（分区容错性）。

一个Eureka中分为eureka server和eureka client。其中eureka server是作为服务的注册与发现中心。eureka client既可以作为服务的生产者，又可以作为服务的消费者。

如图：

简单例子

  • 工具：idea
  • JDK：1.8

服务注册中心

创建一个基础工程Spring Boot，命名：eureka-server，pom.xml内容如下：

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<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <!-- springboot版本与springcloud须匹配 -->
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>eureka-server</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <!-- springboot版本与springcloud须匹配 -->
        <spring.boot.version>2.1.4.RELEASE</spring.boot.version>
        <spring.cloud.version>Greenwich.SR1</spring.cloud.version>
        <spring.maven.version>2.4.1</spring.maven.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-web</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>
                <version>${spring.maven.version}</version>
            </plugin>
        </plugins>
    </build>
</project>

打开application.properties，内容设置为：

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#服务端口
server.port=8077
#服务名称
spring.application.name=eureka-server
#服务地址
eureka.instance.hostname=localhost

#不向注册中心注册自己
eureka.client.register-with-eureka=false
#取消检索服务
eureka.client.fetch-registry=false
#开启注册中心的保护机制，默认是开启
eureka.server.enable-self-preservation=true
#设置保护机制的阈值，默认是0.85。
eureka.server.renewal-percent-threshold=0.5
#注册中心路径，如果有多个eureka server，在这里需要配置其他eureka server的地址，用","进行区分，如"http://address:8888/eureka,http://address:8887/eureka"
eureka.client.service-url.default-zone=http://${eureka.instance.hostname}:${server.port}/eureka

在EurekaServerApplication.java类，加入：

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@EnableEurekaServer

如：
EurekaServerApplication.java类：

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package com.example.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer
@SpringBootApplication
public class EurekaServerApplication {

    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }

}

启动后，打开浏览器输入：http://127.0.0.1:8077/ ，可以看到Eureka面板，其中 Instances currently registered with Eureka 为空，那就证明注册中心没有注册任何服务。

如图：

服务提供者

创建一个基础工程Spring Boot，命名：Demo，pom.xml内容如下：

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<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <!-- springboot版本与springcloud须匹配 -->
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.demo1</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <!-- springboot版本与springcloud须匹配 -->
        <spring.boot.version>2.1.4.RELEASE</spring.boot.version>
        <spring.cloud.version>Greenwich.SR1</spring.cloud.version>
        <spring.maven.version>2.4.1</spring.maven.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.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </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>
        <!-- jar包的名字，默认为project/name节点  -->
        <!--
        <finalName>demo</finalName>
        -->
        <plugins>
            <!--加入插件-->
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring.maven.version}</version>
                <!-- 打jar包注意事项 -->
                <configuration>
                    <!-- 入口类的全限包名 -->
                    <mainClass>com.demo1.demo</mainClass>
                    <layout>JAR</layout>
                </configuration>
            </plugin>
        </plugins>
        <resources>
            <!-- 打包时将jsp文件拷贝到META-INF目录下-->
            <resource>
                <!-- 指定resources插件处理哪个目录下的资源文件 -->
                <directory>src/main/webapp</directory>
                <!--注意此次必须要放在此目录下才能被访问到-->
                <targetPath>META-INF/resources</targetPath>
                <includes>
                    <include>**/**</include>
                </includes>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/**</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <excludes>
                    <exclude>**/*.java</exclude>
                </excludes>
            </resource>
        </resources>
    </build>
</project>

打开application.properties，内容设置为：

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#服务端口
server.port=9091

#服务名称
spring.application.name=hello-service
#eureka注册中心地址
eureka.client.serviceUrl.defaultZone=http://127.0.0.1:8077/eureka/

在DemoApplication.java类，加入：

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@EnableDiscoveryClient

如：
DemoApplication.java类：

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package com.demo1.demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@EnableDiscoveryClient
@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}

创建HelloController.java，代码如下：

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package com.demo1.demo.controller;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;


@RestController
public class HelloController {

    private final Logger logger = LoggerFactory.getLogger(this.getClass());

    @Autowired
    private DiscoveryClient client;//服务发现客户端


    @RequestMapping("/hello")
    public String hello() {
        System.out.println("Hello Spring Boot");
        return "Hello Spring Boot";
    }
}

启动后，日志输出：

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2020-12-12 22:49:40.115  INFO 4408 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_HELLO-SERVICE/PC-20190831IKWQ:hello-service:9091: registering service...
2020-12-12 22:49:40.514  INFO 4408 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_HELLO-SERVICE/PC-20190831IKWQ:hello-service:9091 - registration status: 204

转到Eureka面板，在Instances currently registered with Eureka看到服务的注册信息，

如图：

服务发现与消费

服务发现的任务由Eureka的客户端完成。

服务消费的任务由Ribbon完成。

Ribbon是一个基于HTTP和TCP的客户端负载均衡器，当将Ribbon和Eureka一起使用时，Ribbon会到Eureka注册中心去获取服务端列表，然后进行轮询访问以到达负载均衡的作用，客户端负载均衡也需要心跳机制去维护服务端清单的有效性，当然这个过程需要配合服务注册中心一起完成。

为了实验Ribbon的客户端负载均衡功能，以命令来启动两个不同端口的hello-servicer（服务提供方），

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cd D:\Workspaces\demo\target\

java -jar demo-0.0.1-SNAPSHOT.jar --server.port=9001
java -jar demo-0.0.1-SNAPSHOT.jar --server.port=9002

转到Eureka面板，在Instances currently registered with Eureka看到服务的注册信息，

如图：

创建一个基础工程Spring Boot，命名： demo-consumer，pom.xml内容如下：

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<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <!-- springboot版本与springcloud须匹配 -->
        <version>2.1.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo-consumer</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo-consumer</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <!-- springboot版本与springcloud须匹配 -->
        <spring.boot.version>2.1.4.RELEASE</spring.boot.version>
        <spring.cloud.version>Greenwich.SR1</spring.cloud.version>
        <spring.maven.version>2.4.1</spring.maven.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.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

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

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>

    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring.cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring.maven.version}</version>
            </plugin>
        </plugins>
    </build>
</project>

打开application.properties，内容设置为：

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#服务端口
server.port=9101
#服务名称
spring.application.name=ribbon-consumer
#eureka注册中心地址
eureka.client.serviceUrl.defaultZone=http://127.0.0.1:8077/eureka/

在DemoConsumerApplication.java类，

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package com.example.democonsumer;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.web.client.RestTemplate;

@EnableDiscoveryClient
@SpringBootApplication
public class DemoConsumerApplication {

    @Bean
    // 让RestTemplate在请求时拥有客户端负载均衡的能力
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoConsumerApplication.class, args);
    }
}

创建ConsumerController.java，代码如下：

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package com.example.democonsumer.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@RestController
public class ConsumerController {

    private final Logger logger = LoggerFactory.getLogger(this.getClass());

    @Autowired
    private RestTemplate restTemplate;

    @RequestMapping(value = "/ribbon-consumer", method = RequestMethod.GET)
    public String helloConsumer() {
        //服务提供方服务名称
        String memberUrl = "http://HELLO-SERVICE/hello";
        String result = restTemplate.getForObject(memberUrl, String.class);
        System.out.println("访问结果" + result);
        return result;
    }
}

启动后，日志输出：

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2020-12-13 13:04:59.166  INFO 6620 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_RIBBON-CONSUMER/PC-20190831IKWQ:ribbon-consumer:9101: registering service...
2020-12-13 13:04:59.213  INFO 6620 --- [nfoReplicator-0] com.netflix.discovery.DiscoveryClient    : DiscoveryClient_RIBBON-CONSUMER/PC-20190831IKWQ:ribbon-consumer:9101 - registration status: 204

转到Eureka面板，在Instances currently registered with Eureka看到服务的注册信息，

如图：

打开网址，输入：http://127.0.0.1:9101/ribbon-consumer ， 日志输出：

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2020-12-13 13:07:07.652  INFO 6620 --- [io-9101-exec-10] c.n.l.DynamicServerListLoadBalancer      : DynamicServerListLoadBalancer for client HELLO-SERVICE initialized: DynamicServerListLoadBalancer:{NFLoadBalancer:name=HELLO-SERVICE,current list of Servers=[PC-20190831IKWQ:9001, PC-20190831IKWQ:9002],Load balancer stats=Zone stats: {defaultzone=[Zone:defaultzone;	Instance count:2;	Active connections count: 0;	Circuit breaker tripped count: 0;	Active connections per server: 0.0;]
},Server stats: [[Server:PC-20190831IKWQ:9001;	Zone:defaultZone;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 CST 1970;	First connection made: Thu Jan 01 08:00:00 CST 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]
, [Server:PC-20190831IKWQ:9002;	Zone:defaultZone;	Total Requests:0;	Successive connection failure:0;	Total blackout seconds:0;	Last connection made:Thu Jan 01 08:00:00 CST 1970;	First connection made: Thu Jan 01 08:00:00 CST 1970;	Active Connections:0;	total failure count in last (1000) msecs:0;	average resp time:0.0;	90 percentile resp time:0.0;	95 percentile resp time:0.0;	min resp time:0.0;	max resp time:0.0;	stddev resp time:0.0]
]}ServerList:org.springframework.cloud.netflix.ribbon.eureka.DomainExtractingServerList@6d194ff3

访问结果Hello Spring Boot

从日志可以看到，Ribbon输出了当前客户端维护的服务列表情况：

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NFLoadBalancer:name=HELLO-SERVICE,current list of Servers=[PC-20190831IKWQ:9001, PC-20190831IKWQ:9002]）

Ribbon按此服务列表信息进行轮询访问，以实现基于客户端的负载均衡。在服务消费方，多发送几次请求：http://127.0.0.1:9101/ribbon-consumer ，可以观察判断客户端的负载均衡是否有效。

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