Spring Cloud教程二：Ribbon

前一篇讲了服务注册和发现，没有看过的朋友先看上一篇，这篇是在上一篇基础上展开。

Ribbon简介

Ribbon is a client side load balancer which gives you a lot of control over the behaviour of HTTP and TCP clients. Feign already uses Ribbon, so if you are using @FeignClient then this section also applies.

Ribbon是负载均衡客户端，可以很好的控制HTTP和TCP客户端的行为。 Feign已经集成了Ribbon。

Spring Cloud Netflix默认为ribbon（BeanType beanName：ClassName）提供以下bean：

IClientConfig ribbonClientConfig: DefaultClientConfigImpl
IRule ribbonRule: ZoneAvoidanceRule
IPing ribbonPing: NoOpPing
ServerList<Server> ribbonServerList: ConfigurationBasedServerList
ServerListFilter<Server> ribbonServerListFilter: ZonePreferenceServerListFilter
ILoadBalancer ribbonLoadBalancer: ZoneAwareLoadBalancer

准备工作

这篇文章基于上一篇文章项目，启动eureka-server项目；启动eureka-client项目，端口为8040；将eureka-client的配置文件端口改为8041，并启动,同一个项目修改端口号，启动多个实例，只需要在IDEA中勾选Allow parallel run：

此时你会发现注册服务中注册了两个eureka-client实例，相当于起了2个节点的集群。访问http://localhost:9090:

新建一个服务消费者

使用Spring Initializr新建一个项目，取名为ribbon-service, 在Spring Cloud Discovery中勾选Eureka Discovery Client，在Spring Cloud Routing中勾选Ribbon，在Web中勾选Spring Web:

创建成功后，项目pom.xml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 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.noodles.mars</groupId>
    <artifactId>ribbon-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>ribbon-service</name>
    <description>Ribbon Service</description>

    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>Greenwich.SR3</spring-cloud.version>
    </properties>

    <dependencies>
        <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-netflix-ribbon</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>

ribbon-service配置服务中心地址、应用名、端口，配置文件内容：

server:
  port: 8050

spring:
  application:
    name: ribbon-service

eureka:
  client:
    service-url: 
      defaultZone: http://localhost:9090/eureka/

在项目启动类上注解@EnableDiscoveryClient, 开启向服务中心注册；定义一个 RestTemplate Bean, 并注解@LoadBalanced开启负载均衡功能：

@EnableEurekaClient
@SpringBootApplication
public class RibbonServiceApplication {

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

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

}

写一个controller，通过之前定义的RestTemplate来消费eureka-client服务的/hello接口，url中使用应用名，ribbon会根据应用名来选择具体的服务实例，根据服务实例在请求的时候会用具体的url替换掉服务名：

@RestController
public class HelloController {

    private final RestTemplate restTemplate;

    @Autowired
    public HelloController(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    @GetMapping("/hello")
    public String hello(@RequestParam("name") String name) {
        return restTemplate.getForObject("http://HELLO-ERUEKA-CLIENT/hello?name=" + name, String.class);
    }
}