Spring Cloud的负载均衡Spring Cloud Ribbon和Spring Cloud Feign

一、客户端负载均衡：Spring Cloud Ribbon。

Spring Cloud Ribbon是基于HTTP和TCP的客户端负载工具，它是基于Netflix Ribbon实现的。通过Spring Cloud的封装，可以轻松地将面向服务的REST模板请求，自动转换成客户端负载均衡服务调用。

客户端负载均衡示意图

废话不多说，进入代码实例，通过一个小例子学习一下Ribbon。

Demo实例学习

（1）服务模块介绍：

sc-eureka：服务注册中心，微服务的核心和基础模块，实现各服务的自动化注册与发现。

sc-service_a，sc-service_b：具体的微服务，提供特定的服务，为了实现负载均衡，a、b两个服务具有相同的实例名SERVICE-AB（也可以只创建一个服务SERVICE-AB，同时启动不同的实例）。

sc-customer：微服务消费服务，调用负载均衡客户端调用SERVICE-AB服务。

（2）项目结构与代码实例：

sc-eureka：

maven 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"><modelVersion>4.0.0</modelVersion><groupId>com.springcloud</groupId><artifactId>sc-eureka</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>sc-eureka</name><description>Demo project for Spring Boot</description><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.4.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>Dalston.SR1</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka-server</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>

配置文件application.yml：

server:  port: 1111eureka:  client:    service-url:      default-zone: http://localhost:1111/eureka/ #服务注册中心的地址，供其他服务组件调用进行注册。    fetch-registry: false    register-with-eureka: false  instance:    hostname: localhost  server:    enable-self-preservation: false #在调试时关闭eureka注册中心的保护机制

启动类：ScEurekaApplication.java

package com.springcloud;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;@EnableEurekaServer //启动一个服务注册中心提供给其他应用进行对话@SpringBootApplication //注解等价于以默认属性使用 @Configuration ，@EnableAutoConfiguration 和 @ComponentScan 。public class ScEurekaApplication {public static void main(String[] args) {SpringApplication.run(ScEurekaApplication.class, args);}}

项目结构：

sc-service_a，sc-service_b：

service a，b服务属于同一服务的两个不同实例此处代码只给出service a 的代码结构，service b代码与a并无差别。

maven 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.springcloud</groupId><artifactId>sc-service_a</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>sc-service_a</name><description>Demo project for Spring Boot</description><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.4.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>Dalston.SR1</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</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></plugin></plugins></build></project>

配置文件application.properties（也可写成yml文件，根据个人爱好）：

server.port=1112#配置服务命名，不区分大小写，在注册中心管理界面默认大写显示。spring.application.name=service-ab#指定服务注册中心的地址eureka.client.service-url.defaultZone=http://127.0.0.1:1111/eureka/management.security.enabled=false

启动类：ScServiceAApplication.java

package com.springcloud;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.discovery.EnableDiscoveryClient;@SpringBootApplication@EnableDiscoveryClient //该注解会根据配置文件中的地址，将服务自身注册到服务注册中心public class ScServiceAApplication {public static void main(String[] args) {SpringApplication.run(ScServiceAApplication.class, args);}}

 服务Controller层，ServiceAController.java

package com.springcloud;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;/** * Created by lizheng on 2017/7/20. */@RestControllerpublic class ServiceAController {    @RequestMapping("/info")    public String testA() {        return "hello I am is service A"; //测试代码直接返回一个字符串，不再调用service层等等。    }}

项目结构：

sc-customer_a：

sc-customer_a调用服务中心注册好的服务service-ab，通过负载均衡Ribbon按照默认的负载策略（轮询交替访问a，b）调用服务，通过Spring Cloud Hystrix进行服务的容错保护。具体的负载均衡配置和容错如下配置。

依赖的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"><modelVersion>4.0.0</modelVersion><groupId>com.springcloud</groupId><artifactId>sc-customer_a</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>sc-customer_a</name><description>Demo project for Spring Boot</description><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.4.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>Dalston.SR1</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-ribbon</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!-- 加入断路器依赖 --><dependency><groupId>org.springframework.cloud</groupId>    <artifactId>spring-cloud-starter-hystrix</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>

配置文件application.properties

server.port=1114#为服务命名spring.application.name=ribbon-consumer#指定服务注册中心的地址eureka.client.service-url.defaultZone=http://localhost:1111/eureka/

启动类：ScCustomerAApplication.java（配置负载均衡的RestTemplate，启动容错服务）

package com.springcloud;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;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@EnableCircuitBreaker //开启断路器功能，进行容错管理public class ScCustomerAApplication {@LoadBalanced //开启负载均衡客户端@Bean //注册一个具有容错功能的RestTemplateRestTemplate restTemplate() {return new RestTemplate();}public static void main(String[] args) {SpringApplication.run(ScCustomerAApplication.class, args);}}

Controller层，CustomerAController.java

package com.springcloud;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;/** * Created by lizheng on 2017/7/20. */@RestControllerpublic class CustomerAController {    @Autowired    HelloService service;    @RequestMapping("/ribbon-consumer")    public String coutomerA() {        return service.helloService();    }}

Service层，HelloSrvice.java

package com.springcloud;import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;import org.springframework.web.client.RestTemplate;/** * Created by lizheng on 2017/7/21. */@Servicepublic class HelloService {    @Autowired    RestTemplate restTemplate;    //注解指定发生错误时的回调方法    @HystrixCommand(fallbackMethod = "helloFallBack")    public String helloService() {        //Get请求调用服务，restTemplate被@LoadBalanced注解标记，Get方法会自动进行负载均衡        return restTemplate.getForObject("http://SERVICE-AB/info", String.class);    }    public String  helloFallBack() {        return "Error occurred ！";    }}

项目结构

服务启动并注册成功后，调用sc-customer的‘/ribbon-consumer’会交替调用service a,b返回“hello I am is service A”、“hello I am is service B”，调用出错后会由容错机制返回“Error occurred ！”

二、Spring Cloud的负载均衡与容错Spring Cloud Feign 

第一部分介绍了spring cloud的负载均衡和容错的入门配置，在实际开发中微服务的负载均衡和容错基本同时出现而且是每个服务不可缺少的一部分。在使用ribbon时，通常会使用resttemplate实现对http请求的封装，形成了模板化的调用方法。spring cloud feign在此基础上做了进一步的封装，Feign是一种声明式、模板化的HTTP客户端。在Spring Cloud中使用Feign, 我们可以做到使用HTTP请求远程服务时能与调用本地方法一样的编码体验，开发者完全感知不到这是远程方法，更感知不到这是个HTTP请求。比如：

@Autowiredprivate AdvertGropRemoteService service; // 远程服务public AdvertGroupVO foo(Integer groupId) {    return service.findByGroupId(groupId); // 通过HTTP调用远程服务}

接下来通过入门程序进行学习。

在第一部分服务架构的基础上搭建一个新的服务消费者sc-customer_b，其余服务配置不变。

sc-customer_b的maven 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"><modelVersion>4.0.0</modelVersion><groupId>com.springboot</groupId><artifactId>sc-customer_b</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>sc-customer_b</name><description>Demo project for Spring Boot</description><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>1.5.4.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>Dalston.SR1</spring-cloud.version></properties><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-feign</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></plugin></plugins></build></project>

配置文件application.properties

server.port=1114#为服务命名spring.application.name=ribbon-consumer#指定服务注册中心的地址eureka.client.service-url.defaultZone=http://localhost:1111/eureka/

启动类：ScCustomerBApplication.java

package com.springboot;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.netflix.eureka.EnableEurekaClient;import org.springframework.cloud.netflix.feign.EnableFeignClients;@SpringBootApplication@EnableEurekaClient@EnableFeignClients //开启spring cloud feign的支持public class ScCustomerBApplication {public static void main(String[] args) {SpringApplication.run(ScCustomerBApplication.class, args);}}

Controller层，HelloCotroller.java

package com.springboot;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;/** * Created by lizheng on 2017/7/21. */@RestController()public class HelloCotroller {    @Autowired    HelloService helloService;    @RequestMapping(value = "/feign-customer")    public String helloCustomer() {               return helloService.hello();    }}

为了让Feign知道在调用方法时应该向哪个地址发请求以及请求需要带哪些参数，我们需要定义一个接口,放在service层，HelloService.java

package com.springboot;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.RequestMapping;/** * Created by lizheng on 2017/7/21. */@FeignClient("SERVICE-AB" ) //用于通知Feign组件对该接口进行代理(不需要编写接口实现)， SERVICE-AB代理的具体服务public interface HelloService {    @RequestMapping("/info") //对应具体服务中的接口地址（具体服务controller 层的暴露接口）可以指定具体的get/post    String hello();}

Spring Cloud Feign 的容错，HystrixCommand定义被封装起来，没有办法通过@HystrixCommand注解的fallback，指定服务降级（错误处理）方法。但Spring Cloud Feign提供也更为简洁明了的方法实现服务降级处理。只需要编写一个feign接口的具体实现类即可，比如:

package com.springboot;/** * Created by lizheng on 2017/9/4. */public class HelloServiceFallback implements HelloService {    @Override    public String hello() {        return "request error";    }}

同时在Fegin接口中做一下改变即可：

package com.springboot;import org.springframework.cloud.netflix.feign.FeignClient;import org.springframework.web.bind.annotation.RequestMapping;/** * Created by lizheng on 2017/7/21. */@FeignClient(value = "SERVICE-AB", fallback = HelloServiceFallback.class) //用于通知Feign组件对该接口进行代理(不需要编写接口实现)， SERVICE-AB代理的具体服务public interface HelloService {    @RequestMapping("/info") //对应具体服务中的接口地址（具体服务controller 层的暴露接口）    String hello();}

项目结构

Spring Cloud应用在启动时，Feign会扫描标有@FeignClient注解的接口，生成代理，并注册到Spring容器中。生成代理时Feign会为每个接口方法创建一个RequetTemplate对象，该对象封装了HTTP请求需要的全部信息，请求参数名、请求方法等信息都是在这个过程中确定的，Feign的模板化就体现在这里。通过Feign， 我们能把HTTP远程调用对开发者完全透明，得到与调用本地方法一致的编码体验。这一点与阿里Dubbo中暴露远程服务的方式类似，区别在于Dubbo是基于私有二进制协议，而Feign本质上还是个HTTP客户端。如果是在用Spring Cloud Netflix搭建微服务，那么Feign无疑是最佳选择。（此处文字参考：http://blog.csdn.net/neosmith/article/details/52449921）