Spring Cloud负载均衡之Ribbon

Spring Cloud Ribbon是一个基于http和tcp通讯协议的客户端负载均衡工具，它是基于Netflix Ribbon实现的。它可以独立存在于任何一个微服务系统中，实现远程服务调用和负载均衡。
创建一个spring cloud ribbon服务spring-cloud-ribbon
pom.xml内容如下：

<?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.example</groupId>
    <artifactId>spring-cloud-ribbon</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-cloud-ribbon</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.10.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>Edgware.SR2</spring-cloud.version>
    </properties>

    <dependencies>
        <!-- 此项目为web项目 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- 连接到配置中心依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <!-- 作为客户端被eureka服务发现依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <!-- ribbon依赖 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</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>
            </plugin>
        </plugins>
    </build>

</project>

在SpringCloudRibbonApplication添加@EnableDiscoveryClient注解，表示作为客户端注册到eureka。

添加RestTemplate的bean实例，@LoadBalanced表示实现客户端请求负载均衡，ribbon作为一个客户端服务，注册到eureka中心，eureka根据注册的实例名，查找服务部署，实现负载均衡。

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;

@SpringBootApplication
@EnableDiscoveryClient
public class SpringCloudRibbonApplication {

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

    @Bean
    @LoadBalanced
    RestTemplate restTemplate (){
        return new RestTemplate();
    }
}

application.properties：

#eureka服务端地址
eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
#服务端口号，默认为8080
server.port=8884
#服务注册到eureka的实例名
spring.application.name=spring-cloud-ribbon

创建一个HelloController，代码如下：

import com.perfiffer.example.service.HelloService;
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.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @Autowired
    HelloService helloService;

    @RequestMapping(value = "/hello", method = RequestMethod.GET)
    public String hello(@RequestParam String name) {
        return helloService.hello(name);
    }

}

HelloController调用HelloService的hello方法，HelloService如下：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.client.RestTemplate;

@Service
public class HelloService {

    @Autowired
    RestTemplate restTemplate;

    public String hello(String name) {
        return restTemplate.getForObject("http://SPRING-CLOUD-DEMO/hello?name" + name, String.class);
    }

}

HelloService的hello方法通过restTemplate实例调用远程的服务，SPRING-CLOUD-DEMO为已经注册到eureka中心的服务，SPRING-CLOUD-DEMO为服务的实例名。
spring-cloud-demo工程内容如下：
pom.xml

<?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.example</groupId>
    <artifactId>spring-cloud-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-cloud-demo</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.10.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>Edgware.SR2</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</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>
            </plugin>
        </plugins>
    </build>


</project>

启动类：

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

@SpringBootApplication
@EnableDiscoveryClient
public class SpringCloudDemoApplication {
    
    

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

applicatin.properties：

spring.application.name=spring-cloud-demo
server.port=8887
eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
eureka.instance.prefer-ip-address=true
eureka.instance.instance-id=${spring.cloud.client.ipAddress}:${server.port}

HelloController.java
import com.perfiffer.example.service.IHelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

@Autowired
IHelloService helloService;

@RequestMapping(value = "/hello")
public String hello(@RequestParam String name) {
    return helloService.hello(name);
}

}

IHelloService.java

public interface IHelloService {

    String hello(String name);

}

HelloServiceImpl.java

import com.perfiffer.example.service.IHelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class HelloServiceImpl implements IHelloService {
    
    

    @Override
    public String hello(String name) {
        return "hello, " + name;
    }

}

启动spring-cloud-ribbon，访问http://localhost:8884/hello?tom，可以查看到返回信息hello, tom。如果部署了网关，也可通过网关访问接口。