/**
 * 因為調用目標機器的時候，如果目標機器本身假死或者調用目標不通無法數據返回，那么feign無法打印目標機器。這種場景下我們需要在調用失敗（目標機器沒有返回）的時候也能把目標機器的ip打印出來，這種場景需要我們切入feign選擇機器的邏輯，注入我們自己的調度策略（默認是roundrobin），在里面打印選擇的機器即可。
*/
@Slf4j
public class FeignRule extends RoundRobinRule {

    @Override
    public Server choose(Object key) {
        Server server = super.choose(key);
        if (Objects.isNull(server)) {
            log.info("server is null");
            return null;
        }
        log.info("feign rule ---> serverName:{}, choose key:{}, final server ip:{}", server.getMetaInfo().getAppName(), key, server.getHostPort());
        return server;
    }

    @Override
    public Server choose(ILoadBalancer lb, Object key) {
        Server chooseServer = super.choose(lb, key);

        List<Server> reachableServers = lb.getReachableServers();
        List<Server> allServers = lb.getAllServers();
        int upCount = reachableServers.size();
        int serverCount = allServers.size();
        log.info("serverName:{} upCount:{}, serverCount:{}", Objects.nonNull(chooseServer) ? chooseServer.getMetaInfo().getAppName() : "", upCount, serverCount);
        for (Server server : allServers) {
            if (server instanceof DiscoveryEnabledServer) {
                DiscoveryEnabledServer dServer = (DiscoveryEnabledServer) server;
                InstanceInfo instanceInfo = dServer.getInstanceInfo();
                if (instanceInfo != null) {
                    InstanceInfo.InstanceStatus status = instanceInfo.getStatus();
                    if (status != null) {
                        log.info("serverName:{} server:{}, status:{}", server.getMetaInfo().getAppName(), server.getHostPort(), status);
                    }
                }
            }
        }

        return chooseServer;
    }
}

import org.springframework.cloud.netflix.ribbon.RibbonClients;
import org.springframework.context.annotation.Configuration;
/**
 * @description:feign 配置
 */
@Configuration
@RibbonClients(defaultConfiguration = {FeignRule.class})
public class FeignConfig {
}

@Slf4j
public class CustomRoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalancer {
    final AtomicInteger position;
    final String serviceId;
    ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider;

    public CustomRoundRobinLoadBalancer(ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider, String serviceId) {
        this(serviceInstanceListSupplierProvider, serviceId, (new Random()).nextInt(1000));
    }

    public CustomRoundRobinLoadBalancer(ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider, String serviceId, int seedPosition) {
        this.serviceId = serviceId;
        this.serviceInstanceListSupplierProvider = serviceInstanceListSupplierProvider;
        this.position = new AtomicInteger(seedPosition);
    }

    public Mono<Response<ServiceInstance>> choose(Request request) {
        ServiceInstanceListSupplier supplier = this.serviceInstanceListSupplierProvider.getIfAvailable(NoopServiceInstanceListSupplier::new);
        return supplier.get(request).next().map((serviceInstances) -> {
            return this.processInstanceResponse(supplier, serviceInstances);
        });
    }

    private Response<ServiceInstance> processInstanceResponse(ServiceInstanceListSupplier supplier, List<ServiceInstance> serviceInstances) {
        Response<ServiceInstance> serviceInstanceResponse = this.getInstanceResponse(serviceInstances);
        if (supplier instanceof SelectedInstanceCallback && serviceInstanceResponse.hasServer()) {
            ((SelectedInstanceCallback)supplier).selectedServiceInstance((ServiceInstance)serviceInstanceResponse.getServer());
        }

        return serviceInstanceResponse;
    }

    private Response<ServiceInstance> getInstanceResponse(List<ServiceInstance> instances) {
        if (instances.isEmpty()) {
            if (log.isWarnEnabled()) {
                log.warn("No servers available for service: " + this.serviceId);
            }

            return new EmptyResponse();
        } else {

            int pos = this.position.incrementAndGet() & Integer.MAX_VALUE;
            ServiceInstance instance = instances.get(pos % instances.size());
            log.info("serverName:{} upCount:{}",instance.getServiceId(),instances.size());
            log.info("feign rule ---> serverName:{}, final server ip:{}:{}", instance.getServiceId(), instance.getHost(),instance.getPort());
            return new DefaultResponse(instance);
        }
    }
}

@Configuration
@LoadBalancerClients(defaultConfiguration = CustomLoadBalancerConfiguration.class)
public class CustomLoadBalancerConfig {
}

@Configuration
class CustomLoadBalancerConfiguration {
    /**
     * 參考默認實現
     * @see org.springframework.cloud.loadbalancer.annotation.LoadBalancerClientConfiguration#reactorServiceInstanceLoadBalancer
     * @return
     */
    @Bean
    public ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment, LoadBalancerClientFactory loadBalancerClientFactory) {
        String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
        return new CustomRoundRobinLoadBalancer(loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);
    }
}