使用 Spring Cloud Loadbalancer 实现客户端负载均衡

作者：Grey

原文地址：

博客园：使用 Spring Cloud Loadbalancer 实现客户端负载均衡

CSDN：使用 Spring Cloud Loadbalancer 实现客户端负载均衡

背景

在Spring Cloud G 版发布时提到，
Spring Cloud Netflix 那套组件很多都进入了维护期，如下表所示

同时，针对一些组件，Spring 官方给出了一些替代方案

针对 spring-cloud-ribbon 这个负载均衡组件，Spring 官方提出的替换解决方案是 Spring Cloud Loadbalancer。本文主要通过一个示例介绍了 Spring Cloud Loadbalancer 的基础使用。

环境

JDK 1.8+
Maven 3.5+
Spring Boot 版本：2.7.5
Spring Cloud 版本：2021.0.5

项目结构和说明

spring-cloud-loadbalanced-usage：父项目名称
- server : 服务端端模块
  - src/
  - pom.xml
- client : 客户端模块
  - src/
  - pom.xml
- pom.xml：父项目 pom 配置

流程

整个过程如下示例图

注：Spring Cloud Loadbalancer 是在客户端实现负载均衡策略。

代码说明

服务端主要暴露一个服务，未做特殊配置

    @GetMapping("/greeting")
    public String greet() {
        log.info("Access /greeting");
        int randomNum = rand.nextInt(greetings.size());
        return greetings.get(randomNum);
    }

客户端的核心配置如下，主要是针对负载均衡配置：

package git.snippet.client.config;

import org.springframework.cloud.client.DefaultServiceInstance;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.loadbalancer.annotation.LoadBalancerClient;
import org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Flux;

import java.util.Arrays;
import java.util.List;

@Configuration
@LoadBalancerClient(name = "server")
public class WebClientConfig {

    @LoadBalanced
    @Bean
    WebClient.Builder webClientBuilder() {
        return WebClient.builder();
    }

    @Bean
    @Primary
    ServiceInstanceListSupplier serviceInstanceListSupplier() {
        return new ServiceInstanceListSupplier() {
            @Override
            public String getServiceId() {
                return "server";
            }

            @Override
            public Flux<List<ServiceInstance>> get() {
                return Flux.just(Arrays.asList(
                        new DefaultServiceInstance(getServiceId() + "1", getServiceId(), "localhost", 8090, false),

                        new DefaultServiceInstance(getServiceId() + "2", getServiceId(), "localhost", 9092, false),

                        new DefaultServiceInstance(getServiceId() + "3", getServiceId(), "localhost", 9999, false)));
            }
        };
    }
}

其中 @LoadBalancerClient(name = "server") 指定了服务端的名称；

getServiceId()指定了服务端的服务 ID；

serviceInstanceListSupplier()方法中列出了三个服务端实例的地址；

new DefaultServiceInstance(getServiceId() + "1", getServiceId(), "localhost", 8090, false)
new DefaultServiceInstance(getServiceId() + "2", getServiceId(), "localhost", 9092, false)
new DefaultServiceInstance(getServiceId() + "3", getServiceId(), "localhost", 9999, false)

有了这个配置，在客户端的 Controller 中，做如下注入即可

package git.snippet.client.controller;

import org.springframework.cloud.client.loadbalancer.reactive.ReactorLoadBalancerExchangeFilterFunction;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

@RestController
public class HiController {
    private final WebClient.Builder loadBalancedWebClientBuilder;
    private final ReactorLoadBalancerExchangeFilterFunction lbFunction;


    public HiController(WebClient.Builder loadBalancedWebClientBuilder, ReactorLoadBalancerExchangeFilterFunction lbFunction) {
        this.loadBalancedWebClientBuilder = loadBalancedWebClientBuilder;
        this.lbFunction = lbFunction;
    }

    @RequestMapping("/hi")
    public Mono<String> hi(@RequestParam(value = "name", defaultValue = "Mary") String name) {
        return loadBalancedWebClientBuilder.build().get().uri("http://server/greeting").retrieve().bodyToMono(String.class).map(greeting -> String.format("%s, %s!", greeting, name));
    }

    @RequestMapping("/hello")
    public Mono<String> hello(@RequestParam(value = "name", defaultValue = "John") String name) {
        return WebClient.builder().filter(lbFunction).build().get().uri("http://server/greeting").retrieve().bodyToMono(String.class).map(greeting -> String.format("%s, %s!", greeting, name));
    }
}