SpringCloud 2023 LoadBalancer介绍、使用、获取服务列表原理、负载均衡算法

1. 介绍

功能:

提供客户端的负载均衡算法，将请求均摊到多个服务器上。
属于客户端负载均衡(Nginx属于服务端负载均衡)，会将服务列表缓存到JVM本地，然后客户端自己选择请求服务器
支持Spring Web Flux的WebClient

2. 使用

基本使用可以参考Nacos之SpringCloud集成Nacos注册中心

3 获取服务列表原理

底层是通过DiscoveryClient动态获取所有上线的服务列表。伪代码如下：


@RestController
public class OrderController {

    @Autowired
    private DiscoveryClient discoveryClient;

    @GetMapping("/nacos/getNacosAllServiceInfo")
    public String getNacosAllServiceInfo() {
        List<String> serviceNames = discoveryClient.getServices();
        Map<String, Object> serviceMap = new HashMap<>();
        for (String serviceName : serviceNames) {
            List<ServiceInstance> serviceInstances = discoveryClient.getInstances(serviceName);
            List<Map<String,String>> serviceInstanceInfos = new ArrayList<>();
            for(ServiceInstance serviceInstance: serviceInstances) {
                Map<String, String> serviceInstanceMap = new HashMap<>();
                serviceInstanceMap.put("serviceId", serviceInstance.getServiceId());
                serviceInstanceMap.put("instanceId", serviceInstance.getInstanceId());
                serviceInstanceMap.put("host", serviceInstance.getHost());
                serviceInstanceMap.put("port", String.valueOf(serviceInstance.getPort()));
                serviceInstanceMap.put("uri", serviceInstance.getUri().toString());
                
                serviceInstanceInfos.add(serviceInstanceMap);
            }
            serviceMap.put(serviceName, serviceInstanceInfos);
        }

        return serviceMap.toString();

    }


}

访问http://localhost:8002/nacos/getNacosAllServiceInfo，返回的数据如下：

{orderment=[{instanceId=192.168.163.1#8002#DEFAULT#DEFAULT_GROUP@@orderment, port=8002, host=192.168.163.1, serviceId=orderment, uri=http://192.168.163.1:8002}], payment=[{instanceId=192.168.163.1#8001#DEFAULT#DEFAULT_GROUP@@payment, port=8001, host=192.168.163.1, serviceId=payment, uri=http://192.168.163.1:8001}]}

4. 负载均衡算法

默认的轮询算法RoundRobinLoadBalancer: rest接口第几次请求数 % 服务器集群总数量 = 实际调用服务器位置下标，每次服务重启动后rest接口计数从1开始
同时提供了随机算法RandomLoadBalancer的实现。切换代码如下。说明：
- 实现了LoadBalancerConfig，会使默认的RoundRobinLoadBalancer失效
- 要向哪个服务发送请求，就要在@LoadBalancerClient或@LoadBalancerClients中定义

//@LoadBalancerClient(value = "payment1", configuration = LoadBalancerConfig.class)
@LoadBalancerClients({
        @LoadBalancerClient(value = "payment1", configuration = LoadBalancerConfig.class),
        @LoadBalancerClient(value = "payment2", configuration = LoadBalancerConfig.class),
})
public class LoadBalancerConfig {

    @Bean
    ReactorLoadBalancer<ServiceInstance> randomLoadBalancer(Environment environment,
                                                            LoadBalancerClientFactory loadBalancerClientFactory) {
        String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
        return new RandomLoadBalancer(loadBalancerClientFactory
                .getLazyProvider(name, ServiceInstanceListSupplier.class),
                name);
    }
}