官方的靜態lb已經滿足大部分場景

缺點是全靜態，動態擴充套件能力不強

動態擴充套件有兩個方向

方式一 是聚焦於spring-cloud-gateway本身，實現一些自定義的方法
方式二 是依賴spring-cloud的生態，consul/nacos註冊中心,或config配置中心，bus事件佇列動態更新配置等

做es的閘道器依賴spring-cloud，太重，方案放棄了

個人一開始以為沒有靜態lb的支援，所以直接就看方式一，所實際這個需求，靜態基本就滿足，但也不算完全是白折騰，至少更熟悉了spring-cloud-gateway的程式碼和機制

server:
  port: 9208
spring:
  cloud:
    gateway:
      enabled: true
    discovery:
      client:
        simple:
          instances:
            es3[0]:
              uri: http://127.0.0.1:19200
            es3[1]:
              uri: http://127.0.0.1:19201
            es3[2]:
              uri: http://127.0.0.1:19202
          order: 1
 

spring-cloud-gateway 原生本地代理，配置resource即可

純靜態有兩個缺點
1 無法動態新增或刪除節點，如instances下 新增es[3] ,刪除可以自動檢測遮蔽，新增就不好做了
2 即使無法動態新增，手動更改配置，再重啟節點也滿足要求

自定義方式一

實現ServiceInstanceListSupplier

public class CustomServiceInstanceListSupplier  implements ServiceInstanceListSupplier {

    public CustomServiceInstanceListSupplier() {
    }
    private String aaaa;

    @Override
    public String getServiceId() {
        return "es2";
    }

    @Override
    public Flux<List<ServiceInstance>> get() {
        List<ServiceInstance> sis=new ArrayList<>();
        sis.add(0, new DefaultServiceInstance("instanceId-4","es2","127.0.0.1",9204,false));
        sis.add(1, new DefaultServiceInstance("instanceId-5","es2","127.0.0.1",9205,false));
        System.out.println("get()");
        return Flux.defer(() -> {
            return Flux.just(sis);
        });
    }

    @Override
    public Flux<List<ServiceInstance>> get(Request request) {
        return get();
    }
}
---
	@Bean
	public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(
			ConfigurableApplicationContext context) {
		return ServiceInstanceListSupplier.builder()
				.withBase(new CustomServiceInstanceListSupplier())
//				.withHints()
//				.withHealthChecks()
				.build(context);
	}
 

自定義方式二，與方式一類似

實現DiscoveryClient 並結合DiscoveryClientServiceInstanceListSupplier使用

public class CustomDiscoveryClient implements DiscoveryClient {
    private List<ServiceInstance> instances;
    private String myServiceId;
    public CustomDiscoveryClient(List<ServiceInstance> instances) {
        this.myServiceId=myServiceId;
        this.instances=instances;
        loadInstancesFromRemote();
    }
    public void loadInstancesFromRemote(){
        List<ServiceInstance> serviceInstanceList2=new ArrayList<>();
        serviceInstanceList2.add(0, new DefaultServiceInstance("instanceId-0","ces2","127.0.0.1",9200,false));
        setInstances(serviceInstanceList2);
    }

    public String getMyServiceId() {
        return myServiceId;
    }

    public void setInstances(List<ServiceInstance> instances) {
        this.instances=instances;
    }

    @Override
    public String description() {
        return null;
    }

    @Override
    public List<ServiceInstance> getInstances(String serviceId) {
        return this.instances;
    }
    @Override
    public List<String> getServices() {
        return null;
    }

}

@Bean
	public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(
			ConfigurableApplicationContext context) {
    		CustomDiscoveryClient cdc2=new CustomDiscoveryClient(null);
		  DiscoveryClientServiceInstanceListSupplier listSupplier=new        DiscoveryClientServiceInstanceListSupplier(cdc2,context.getEnvironment());
		return ServiceInstanceListSupplier.builder()
				.withBase(listSupplier)
				.build(context);
	}
 

再提供一個外部的webapi,新增或刪除節點，則一個基本的動態lb功能就完備了

新增lb節點，刪除lb節點，載入配置使lb變更生效

自定義方式三

    @Bean
   ReactorLoadBalancer<ServiceInstance> randomLoadBalancer(Environment environment,
                                             LoadBalancerClientFactory loadBalancerClientFactory) {
      return new RandomLoadBalancer(loadBalancerClientFactory
            "es");
   }

方式三功能最細緻

簡而方式，方式一/方式二，都是註冊全域性的ServiceInstanceListSupplier，全域性生效

方式三，自定義返回 RandomLoadBalancer，建構函式包含ServiceInstanceListSupplier，可以在外層生成對應的ServiceInstanceListSupplier

    public RandomLoadBalancer(ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider, String serviceId) {
        this.serviceId = serviceId;
        this.serviceInstanceListSupplierProvider = serviceInstanceListSupplierProvider;
    }    

也可以完全不依賴官方的ServiceInstanceListSupplier，實現完全自定義的ReactorLoadBalancer