SpringCloud之Eureka：集群搭建

上篇文章《SpringCloud之Eureka：服务发布与调用例子》实现了一个简单例子，这次对其进行改造，运行两个服务器实例、两个服务提供者实例，服务调用者请求服务，使其可以进行集群部署。

集群结构如下图所示。

 由于开发环境只有一台电脑，要构建集群，需要修改hosts文件，在里面添加主机名映射。

127.0.0.1 slave1 slave2

一、服务器端

1、创建项目

开发工具：IntelliJ IDEA 2019.2.2
IDEA中创建一个新的SpringBoot项目，名称为“first-cloud-server”，SpringBoot版本选择2.1.9，在选择Dependencies(依赖)的界面勾选Spring Cloud Discovert ->
Eureka Server，创建完成后的pom.xml配置文件自动添加SpringCloud最新稳定版本依赖，当前为Greenwich.SR3。
pom.xml完整内容可参考上篇文章《SpringCloud之Eureka：服务发布与调用例子》。

2、修改配置application.yml

由于需要对同一个应用程序启动两次，因此需要使用profiles配置。
下面配置了两个profiles，名称分别为slave1和slave2，当使用slave1启动服务器后，会向http://slave2:8762/eureka/注册自己，当使用slave2启动服务器后，会向
http://slave1:8761/eureka/注册自己，即两个服务器启动后，互相注册。 

server:
  port: 8761
spring:
  application:
    name: first-cloud-server
  profiles: slave1
eureka:
  instance:
    hostname: slave1
  client:
    serviceUrl:
      defaultZone: http://slave2:8762/eureka/
---
server:
  port: 8762
spring:
  application:
    name: first-cloud-server
  profiles: slave2
eureka:
  instance:
    hostname: slave2
  client:
    serviceUrl:
      defaultZone: http://slave1:8761/eureka/

3、修改启动类代码FirstEkServerApplication.java

除了增加注解@EnableEurekaServer，还让类在启动时读取控制台输入，决定使用哪个profiles来启动服务器。 

package com.example.firstcloudserver;

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

import java.util.Scanner;

@SpringBootApplication
@EnableEurekaServer
public class FirstCloudServerApplication {

    public static void main(String[] args) {
        //SpringApplication.run(FirstCloudServerApplication.class, args);
        Scanner scan = new Scanner(System.in);
        String profiles = scan.nextLine();
        new SpringApplicationBuilder(FirstCloudServerApplication.class)
                .profiles(profiles).run(args);
    }

}

二、编写服务提供者

1、创建项目

IDEA中创建一个新的SpringBoot项目，除了名称为“first-cloud-provider”，其它步骤和上面创建服务器端一样。

2、修改配置application.yml

spring:
  application:
    name: first-cloud-provider
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/,http://localhost:8762/eureka/

3、添加类 User.java

package com.example.firstcloudprovider;

public class User {
    private Integer id;
    private String name;
    private String message;

    public User(Integer id, String name){
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

4、添加控制器 UserController.java

package com.example.firstcloudprovider;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;

@RestController
public class UserController {
    @RequestMapping(value = "/user/{userId}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public User findUser(@PathVariable("userId") Integer userId, HttpServletRequest request){
        User user = new User(userId, "gdjlc");
        user.setMessage(request.getRequestURL().toString());
        return user;
    }
}

5、修改启动类代码FirstCloudProviderApplication.java

除了增加注解@EnableEurekaClient，还让类在启动时读取控制台输入，决定使用哪个端口启动服务器。 

package com.example.firstcloudprovider;

//import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

import java.util.Scanner;

@SpringBootApplication
@EnableEurekaClient
public class FirstCloudProviderApplication {

    public static void main(String[] args) {
        //SpringApplication.run(FirstCloudProviderApplication.class, args);
        Scanner scan = new Scanner(System.in);
        String port = scan.nextLine();
        new SpringApplicationBuilder(FirstCloudProviderApplication.class).properties("server.port=" + port).run(args);
    }

}

三、编写服务调用者

1、创建项目
IDEA中创建一个新的SpringBoot项目，除了名称为“first-cloud-invoker”，其它步骤和上面创建服务器端一样。

2、修改配置application.yml

server:
  port: 9000
spring:
  application:
    name: first-cloud-invoker
eureka:
  instance:
    hostname: localhost
  client:
    serviceUrl:
      defaultZone: http://slave1:8761/eureka/,http://slave2:8762/eureka/

3、添加控制器 InvokerController.java

package com.example.firstcloudinvoker;

import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
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;

@RestController
@Configuration
public class InvokerController {
    @Bean
    @LoadBalanced
    public RestTemplate getRestTemplate(){
        return new RestTemplate();
    }

    @RequestMapping(value = "/router", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public String router(){
        RestTemplate restTpl = getRestTemplate();
        //根据应用名称调用服务
        String json = restTpl.getForObject("http://first-cloud-provider/user/1", String.class);
        return json;
    }
}

4、修改启动类代码FirstCloudInvokerApplication.java

添加注解@EnableDiscoveryClient，使得服务调用者可以去Eureka中发现服务。 

package com.example.firstcloudinvoker;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class FirstCloudInvokerApplication {

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

}

四、编写REST客户端进行测试

1、创建项目

IDEA中创建一个新的SpringBoot项目，名称为“first-cloud-rest-client”，SpringBoot版本选择2.1.9，在选择Dependencies(依赖)的界面勾选Web->Spring Web。
在pom.xml中增加httpclient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 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>
        <version>2.1.9.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>first-cloud-rest-client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>first-cloud-rest-client</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <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.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

2、修改配置application.yml

server:
  port: 9001

3、修改启动类代码FirstCloudRestClientApplication.java

 编写调用REST服务的代码

package com.example.firstcloudrestclient;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
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;

@SpringBootApplication
@RestController
public class FirstCloudRestClientApplication {

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

    @RequestMapping("/")
    public String testHttpClient(){
        StringBuilder sb = new StringBuilder();
        try{
            CloseableHttpClient httpClient = HttpClients.createDefault();
            for(int i=0;i<10;i++){
                HttpGet httpGet = new HttpGet("http://localhost:9000/router");
                HttpResponse response = httpClient.execute(httpGet);
                sb.append(EntityUtils.toString(response.getEntity()) + "<br />");
            }
        }catch(Exception ex){
            return ex.getMessage();
        }
        return sb.toString();
    }
}

4、测试

（1）启动两个服务器端，在控制台中分别输入slave1和slave2启动。
（2）启动两个服务提供者，在控制台中分别输入8763和8764启动。
（3）启动服务调用者。
（4）启动REST客户端。

浏览器访问 http://slave1:8761/，页面如下

 浏览器访问 http://slave2:8762/，页面如下

 浏览器访问 http://localhost:8763/user/1，页面输出：

{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}

浏览器访问 http://localhost:8764/user/1，页面输出：

{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}

浏览器访问 http://localhost:9000/router，多次刷新页面，页面输出在8763和8764切换：

{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}

{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}

浏览器访问 http://localhost:9001/，页面输出 

{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8764/user/1"}
{"id":1,"name":"gdjlc","message":"http://localhost:8763/user/1"}

请求了10次，8763和8764分别被请求5次，可见已经达到负载均衡。