Eureka入门教程

一如码农深似海，今朝有酒今朝醉。入坑已经五年多了，人总有所坚持，立个flag，想把spring、springboot、springcloud从入门教程到源码分析，希望能对于读者有用，ekko写文章喜欢详尽，源代码有点多，不喜勿喷。

环境搭建

IDEA（个人推荐，功能强大不多说）、其次Spring Tools 4，工作这么多年，很大牛用这工具，也是不错的选择；其次eclipse。
jdk1.8环境。（google或者百度）
maven（gradle少部分公司用，暂不介绍，当然，gradle更强大）

版本

参考官方https://spring.io/projects/spring-cloud

spring cloud版本	springboot版本
Hoxton	2.2.x
Greenwich	2.1.x
Finchley	2.0.x
Edgware	1.5.x
Dalston	1.5.x

我选择spring cloud Hoxton.SR4、springboot版本2.2.5.RELEASE。（如果是公司项目建议用老版本，原因无它，坑少网上解决办法多）。

父级pom.xml文件

<?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.duoduo</groupId>
    <artifactId>duoduo-parent</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Hoxton.SR4</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>2.2.5.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

        </dependencies>
    </dependencyManagement>



    <build>
        <finalName>duoduo-parent</finalName>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <filtering>true</filtering>
            </resource>
        </resources>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-resources-plugin</artifactId>
                <configuration>
                    <delimiters>
                        <delimit>$</delimit>
                    </delimiters>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <modules>
        <module>duoduo-eureka</module>
        <module>duoduo-provider-service</module>
    </modules>
</project>

duoduo-eureka子项目POM文件

<?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">
    <parent>
        <artifactId>duoduo-parent</artifactId>
        <groupId>com.duoduo</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>duoduo-eureka</artifactId>

    <dependencies>

        <!--eureka-server服务端 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>

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

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


        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>
</project>

eureka启动类

package com.duoduo.cloud;

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

/**
 * @author ekko
 * eureka启动类
 */
@SpringBootApplication
@EnableEurekaServer
public class ServerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ServerApplication.class,args);
              // 官方文档，编译报错，编译报错，可以使用下面代码，个人还是喜欢上面那行代码，启动
              //new SpringApplicationBuilder(ServerApplication.class)
                .web(true).run(args);
      //new SpringApplicationBuilder(ServerApplication.class)
                .web(WebApplicationType.SERVLET).run(args);
      

    }

}

application.yml文件

server:
  port: 8761  #端口

eureka:
  instance:
    hostname: localhost #eureka服务端的实例名称
  client:
    registerWithEureka: false #false表示不向注册中心注册自己。
    fetchRegistry: false #false表示自己端就是注册中心，我的职责就是维护服务实例，并不需要去检索服务
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/ #设置与Eureka Server交互的地址查询服务和注册服务都需要依赖这个地址。

ServerApplication方法启动

2020-05-23 14:49:39.025  INFO 8031 --- [      Thread-17] c.n.e.r.PeerAwareInstanceRegistryImpl    : Renew threshold is: 1
2020-05-23 14:49:39.025  INFO 8031 --- [      Thread-17] c.n.e.r.PeerAwareInstanceRegistryImpl    : Changing status to UP
2020-05-23 14:49:39.042  INFO 8031 --- [      Thread-17] e.s.EurekaServerInitializerConfiguration : Started Eureka Server
2020-05-23 14:49:39.112  INFO 8031 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8761 (http) with context path ''
2020-05-23 14:49:39.114  INFO 8031 --- [  restartedMain] .s.c.n.e.s.EurekaAutoServiceRegistration : Updating port to 8761

控制台显示以上信息说明，eureka服务端启动成功。可以访问http://localhost:8761/。

duoduo-provider-service POM文件

<?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">
    <parent>
        <artifactId>duoduo-parent</artifactId>
        <groupId>com.duoduo</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>duoduo-provider-service</artifactId>

    <dependencies>
        <!--eureka-server服务端 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</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-actuator</artifactId>
        </dependency>

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

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </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-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>
</project>

启动类

package com.duoduo.cloud;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * @author ekko 不需要添加@EnableEurekaClient,后续有说明
 * eureka启动类
 */
@SpringBootApplication
@RestController
public class ServiceApplication {

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

    @RequestMapping("/")
    public String home() {
        return "Hello world";
    }

}

application.yml

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
spring:
  application:
    name: DUODUO-PROVIDER-SERVICE # 项目服务名,如果不写服务名，默认服务名UNKNOWN

启动ServiceApplication方法。在访问http://localhost:8761/，会发现eureka控制台Instances currently registered with Eureka多了一个DUODUO-PROVIDER-SERVICE的服务。

可能遇到问题

eureka自我保护机制（不用看到控制台保红就认为eureka出问题了）

不知道广大读者有没有了解过CAP模型，eureka是典型AP模型，这里提一句题外话，zookeeper是典型的CP模型，在eureka server运行期间，会统计客户端心跳的比例，15分钟是否超过85%，超过则把会把实例注册信息保护起来。再说一嘴zookeeper，在zk集群中，网络出现问题，zk重新选举leader，需要耗费不少的时间，这个期间，不可以zk注册服务，而eureka不同，可以继续注册。原因说这么多，面试官经常会问zk、eureka的区别。这就是这道题的痛点吧。

github地址

https://github.com/itekko/duoduo-parent.git