1. 理论知识
2. 自定义负载均衡
3. Spring Cloud LoadBalanced实现
4. Netflix Ribbon 实现

Spring Cloud负载均衡

版本信息

Spring Cloud : Hoxton.SR1

Spring Boot : 2.2.2.RELEASE

Zookeeper : 3.5.6 （注册中心使用）

理论知识

负载均衡分为4层负载和7层负载（4层和7层负载是针对网络协议），还可以分为客户端负载和服务端负载

• 4层负载 一般来说是硬件负载，比如F5
• 7层负载 一般来说是软件负载，比如Nginx

OSI模型(Open System Interconnection Reference Model 开放式系统互联通信参考模型)

1. 物理层
2. 数据链路层
3. 网络层
4. 传输层
5. 会话层
6. 表达层
7. 应用层

常见负载均衡算法

• Round Robin 轮询

• Random 随机

• Hash 哈希

• Least Connections 最小连接数

• Least Time 最少时间

• Least Response Times 最小响应时间

自定义负载均衡

服务端

一个简单的对外提供服务，基于Zookeeper注册中心

1. 添加pom依赖

   <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>
   <!--zookeeper 客户端-->
   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-zookeeper-discovery</artifactId>
   </dependency>

2. 简单的对外提供服务端点

   /**
    * 服务提供端点
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @RestController
   public class EchoController {
   
       @Autowired
       private Environment environment;
   
   
       @GetMapping("/echo")
       public String echo(String message) {
           // 由于采用的是随机端口，这地方必须采用这个方式获取端口
           String port = environment.getProperty("local.server.port");
           return "ECHO(" + port + "):" + message;
       }
   }

3. 配置文件application.yml

   spring:
     application:
       name: load-balance-server
     cloud:
       zookeeper:
         connect-string: 127.0.0.1:2181
   server:
     port: 0

4. 服务启动程序类LoadBalanceServerApplication

   /**
    * 负载均衡服务端启动程序
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @SpringBootApplication
   public class LoadBalanceServerApplication {
   
       public static void main(String[] args) {
           SpringApplication.run(LoadBalanceServerApplication.class, args);
       }
   }

   启动服务，根据启动日志查看本地的随机端口，此次端口是50939

   http://127.0.0.1:50939/echo?message=Hello 返回信息ECHO(50939):Hello

客户端

了解RestTemplate核心api

• org.springframework.web.client.RestTemplate Rest客户端模板
• org.springframework.http.client.ClientHttpRequestFactory http客户端请求工厂
  • org.springframework.http.client.SimpleClientHttpRequestFactory 简单实现（JDK）
  • org.springframework.http.client.HttpComponentsClientHttpRequestFactory apache HTTP组件实现
  • org.springframework.http.client.OkHttp3ClientHttpRequestFactory OkHttp实现
• org.springframework.http.client.ClientHttpRequest http客户端请求
  • org.springframework.http.HttpRequest http 请求信息
    • org.springframework.http.HttpMessage http请求头信息
  • org.springframework.http.HttpOutputMessage http返回信息
    • org.springframework.http.HttpMessage http请求头信息
• org.springframework.http.client.ClientHttpResponse http客户端返回信息

序列化与反序列化是通过Spring MVC组件进行转换

• org.springframework.http.converter.HttpMessageConverter http信息转换

1. 添加pom依赖

   <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>
   <!--zookeeper 客户端-->
   <dependency>
       <groupId>org.springframework.cloud</groupId>
       <artifactId>spring-cloud-starter-zookeeper-discovery</artifactId>
   </dependency>

2. 客户端提供服务端点

   /**
    * 服务提供端点
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @RestController
   public class EchoController {
   
       @Autowired
       private RestTemplate restTemplate;
   
       @GetMapping("/{serveName}/echo/{message}")
       public String echo(@PathVariable String serveName,@PathVariable String message) {
           return restTemplate.getForObject("http://"+serveName+"/echo?message=" + message, String.class);
       }
       
   }

3. 配置文件application.yml

   spring:
     application:
       name: load-balance-client
     cloud:
       zookeeper:
         connect-string: 127.0.0.1:2181
   server:
     port: 8080

4. RestTemplate拦截器LoadBalancedRequestInterceptor

   /**
    * 自定义实现负载均衡拦截器
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @Component
   public class LoadBalancedRequestInterceptor implements ClientHttpRequestInterceptor {
   
       @Autowired
       private DiscoveryClient discoveryClient;
   
   
       @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)
               throws IOException {
           URI uri = request.getURI();
           // 主机名
           String host = uri.getHost();
           List<ServiceInstance> instances = this.discoveryClient.getInstances(host);
           // 暂不考虑没有服务的情况
           int size = instances.size();
           // 随机
           int index = new Random().nextInt(size);
           ServiceInstance instance = instances.get(index);
           String url = (instance.isSecure() ? "https://" : "http://") +
                   instance.getHost() + ":" + instance.getPort()+uri.getPath()+"?"+uri.getQuery();
           // 客户端调用
           ClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
           ClientHttpRequest clientHttpRequest = requestFactory.createRequest(URI.create(url), request.getMethod());
           return clientHttpRequest.execute();
       }
   }

5. 服务启动程序类LoadBalanceServerApplication

   **
    * 负载均衡客户端启动程序
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @SpringBootApplication
   public class LoadBalanceClientApplication {
   
       public static void main(String[] args) {
           SpringApplication.run(LoadBalanceClientApplication.class, args);
       }
   
       @Bean
       @Autowired
       public RestTemplate restTemplate(LoadBalancedRequestInterceptor interceptor){
           RestTemplate restTemplate = new RestTemplate();
           restTemplate.setInterceptors(Collections.singletonList(interceptor));
           return restTemplate;
       }
   
   }

   启动服务，http://127.0.0.1:8090/load-balance-server/echo/hello 返回信息ECHO(51157):hello

Spring Cloud LoadBalanced实现

• Spring RestTemplate as a Load Balancer Client
• Spring WebClient as a Load Balancer Client
• Spring WebFlux WebClient with ReactorLoadBalancerExchangeFilterFunction

@LoadBalanced注解分析

@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Qualifier
public @interface LoadBalanced {

}

@Qualifier注解的作用

• 配置value的时候 根据Bean的名称（name）或者别名(alias)进行查找
• 没有配置的时候 标识分类

示例:

/**
 * {@link Qualifier}应用
 *
 * @author xcl <xcl@winning.com.cn>
 * @date 2020/2/4
 */
@SpringBootApplication
public class QualifierApplication  implements ApplicationRunner {

    @Bean
    public String a(){
        return "bean-a";
    }

    @Bean
    @Qualifier
    public String b(){
        return "bean-b";
    }

    @Bean
    @Qualifier
    public String c(){
        return "bean-c";
    }

    @Autowired
    private Map<String,String> beans;

    @Autowired
    @Qualifier
    private Map<String, String> qualifierBeans;

    public static void main(String[] args) {
        new SpringApplicationBuilder(QualifierApplication.class)
                .web(WebApplicationType.NONE)
                .run(args);
    }

    @Override
    public void run(ApplicationArguments args) throws Exception {
        System.out.println(beans);
        System.out.println(qualifierBeans);
    }
}

打印结果：

{a=bean-a, b=bean-b, c=bean-c}
{b=bean-b, c=bean-c}

从结果可知：Bean b 和Bean c根据@Qualifier进行了分组

@LoadBalanced注解使用

1. 客户端注册@LoadBalanced的RestTemplate

   /**
    * 负载均衡客户端启动程序
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @SpringBootApplication
   public class LoadBalanceClientApplication {
   
       public static void main(String[] args) {
           SpringApplication.run(LoadBalanceClientApplication.class, args);
       }
   
       @Bean
       @Autowired
       public RestTemplate restTemplate(LoadBalancedRequestInterceptor interceptor){
           RestTemplate restTemplate = new RestTemplate();
           restTemplate.setInterceptors(Collections.singletonList(interceptor));
           return restTemplate;
       }
   
   
       @Bean
       @LoadBalanced
       public RestTemplate lbRestTemplate(){
           return new RestTemplate();
       }
   
   }

2. 调整客户端提供服务端点

   /**
    * 服务提供端点
    *
    * @author FelixFly <chenglinxu@yeah.net>
    * @date 2020/2/4
    */
   @RestController
   public class EchoController {
   
       @Autowired
       private RestTemplate restTemplate;
   
       @Autowired
       @LoadBalanced
       private RestTemplate lbRestTemplate;
   
       @GetMapping("/{serveName}/echo/{message}")
       public String echo(@PathVariable String serveName,@PathVariable String message) {
           return restTemplate.getForObject("http://"+serveName+"/echo?message=" + message, String.class);
       }
   
   
       @GetMapping("/{serveName}/lb-echo/{message}")
       public String lbEcho(@PathVariable String serveName,@PathVariable String message) {
           return lbRestTemplate.getForObject("http://"+serveName+"/echo?message=" + message, String.class);
       }
   
   }

   启动服务，http://127.0.0.1:8090/load-balance-server/lb-echo/hello 返回信息ECHO(51157):hello

@LoadBalanced核心api

• org.springframework.cloud.client.loadbalancer.LoadBalancerInterceptor 负载均衡的RestTemplate拦截器

• org.springframework.cloud.client.loadbalancer.LoadBalancerClient 负载均衡的客户端

  • org.springframework.cloud.client.loadbalancer.ServiceInstanceChooser 服务实例选择器

  实现类：

  • org.springframework.cloud.loadbalancer.blocking.client.BlockingLoadBalancerClient Spring Cloud LoadBalancer实现
  • org.springframework.cloud.netflix.ribbon.RibbonLoadBalancerClient Ribbon实现类

• org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier 服务实例列表生成器

  基于DiscoveryClient和ReactiveDiscoveryClient实现：org.springframework.cloud.loadbalancer.core.DiscoveryClientServiceInstanceListSupplier

• org.springframework.cloud.loadbalancer.core.ReactorServiceInstanceLoadBalancer 响应式服务实例负载均衡器

  • org.springframework.cloud.loadbalancer.core.ReactorLoadBalancer 响应式负载均衡器
    • org.springframework.cloud.client.loadbalancer.reactive.ReactiveLoadBalancer 响应式的负载均衡器

  默认实现是轮询的负载均衡器：org.springframework.cloud.loadbalancer.core.RoundRobinLoadBalancer

  仅且仅有这一种实现

Netflix Ribbon 实现

核心api

Ribbon客户端配置类org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration

• com.netflix.loadbalancer.ILoadBalancer 负载均衡接口

  默认实现：com.netflix.loadbalancer.ZoneAwareLoadBalancer

  父类：com.netflix.loadbalancer.DynamicServerListLoadBalancer 动态服务列表负载均衡器

• com.netflix.client.config.IClientConfig 客户端配置

  默认实现：com.netflix.client.config.DefaultClientConfigImpl

• com.netflix.loadbalancer.IRule 负载规则

  默认实现：com.netflix.loadbalancer.ZoneAvoidanceRule

  • com.netflix.loadbalancer.RandomRule 随机
  • com.netflix.loadbalancer.RoundRobinRule 轮询
  • com.netflix.loadbalancer.WeightedResponseTimeRule 响应时间权重
  • com.netflix.loadbalancer.BestAvailableRule 最大可用
  • org.springframework.cloud.zookeeper.discovery.dependency.StickyRule 粘性（返回同一个实例）

• com.netflix.loadbalancer.IPing 存活检测

  默认实现：com.netflix.loadbalancer.DummyPing 一直存活

• com.netflix.loadbalancer.ServerList 服务列表

  默认实现：com.netflix.loadbalancer.ConfigurationBasedServerList 配置的服务列表（静态服务列表）

  配置参数：{severName}.ribbon.listOfServers

  动态服务列表

  • com.netflix.niws.loadbalancer.DiscoveryEnabledNIWSServerList Eureka服务列表

  • org.springframework.cloud.consul.discovery.ConsulServerList consul服务列表

  • org.springframework.cloud.zookeeper.discovery.ZookeeperServerList Zookeeper服务列表

  • com.alibaba.cloud.nacos.ribbon.NacosServerList Nacos服务列表

  缺少了一种基于DiscoveryClient的动态服务列表实现

• com.netflix.loadbalancer.ServerListFilter 服务列表过滤器

  默认实现: org.springframework.cloud.netflix.ribbon.ZonePreferenceServerListFilter

• com.netflix.loadbalancer.ServerListUpdater 服务列表更新器

  默认实现：com.netflix.loadbalancer.PollingServerListUpdater 服务列表轮询更新器

  • com.netflix.niws.loadbalancer.EurekaNotificationServerListUpdater Eureka服务列表更新器

备注

As Spring Cloud Ribbon is now under maintenance, we suggest you set spring.cloud.loadbalancer.ribbon.enabled to false, so that BlockingLoadBalancerClient is used instead of RibbonLoadBalancerClient.

由于Spring Cloud Ribbon正在维护，官方推荐使用spring.cloud.loadbalancer.ribbon.enabled设置为false（禁用Ribbon），BlockingLoadBalancerClient 替代RibbonLoadBalancerClient。