参考：org.springframework.cloud.netflix.ribbon.RibbonClientConfiguration
IClientConfig：Ribbon的客户端配置，默认采用DefaultClientConfigImpl实现。IRule：Ribbon的负载均衡策略，默认采用ZoneAvoidanceRule实现，该策略能够在多区域环境下选出最佳区域的实例进行访问。IPing：Ribbon的实例检查策略，默认采用DummyPing实现，该检查策略是一个特殊的实现，实际上它并不会检查实例是否可用，而是始终返回true，默认认为所有服务实例都是可用的。ServerList：服务实例清单的维护机制，默认采用ConfigurationBasedServerList实现。ServerListFilter：服务实例清单过滤机制，默认采ZonePreferenceServerListFilter，该策略能够优先过滤出与请求方处于同区域的服务实例。ILoadBalancer：负载均衡器，默认采用ZoneAwareLoadBalancer实现，它具备了区域感知的能力。 Ribbon负载均衡策略 RandomRule：随机选择一个Server。RetryRule：对选定的负载均衡策略机上重试机制，在一个配置时间段内当选择Server不成功，则一直尝试使用subRule的方式选择一个可用的server。RoundRobinRule：轮询选择，轮询index，选择index对应位置的Server。AvailabilityFilteringRule：过滤掉一直连接失败的被标记为circuit tripped的后端Server，并过滤掉那些高并发的后端Server或者使用一个AvailabilityPredicate来包含过滤server的逻辑，其实就是检查status里记录的各个Server的运行状态。BestAvailableRule：选择一个最小的并发请求的Server，逐个考察Server，如果Server被tripped了，则跳过。WeightedResponseTimeRule：根据响应时间加权，响应时间越长，权重越小，被选中的可能性越低。ZoneAvoidanceRule：默认的负载均衡策略，即复合判断Server所在区域的性能和Server的可用性选择Server，在没有区域的环境下，类似于轮询NacosRule: 优先调用同一集群的实例，基于随机权重 修改默认负载均衡策略 全局配置全局配置：所有调用的微服务一律使用指定的负载均衡策略，只需要向容器中注入IRule实例即可。
package com.morris.user.config;import com.alibaba.cloud.nacos.ribbon.NacosRule;import com.netflix.loadbalancer.IRule;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configurationpublic class RibbonConfig {@Beanpublic IRule ribbonRule() {// 指定使用Nacos提供的负载均衡策略（优先调用同一集群的实例，基于随机权重）return new NacosRule();}} 局部配置局部配置：可以在配置文件中调用指定微服务时，使用对应的负载均衡策略。
# 被调用的微服务名order-service:ribbon:# 指定使用Nacos提供的负载均衡策略（优先调用同一集群的实例，基于随机&权重）NFLoadBalancerRuleClassName: com.alibaba.cloud.nacos.ribbon.NacosRule 自定义负载均衡策略通过实现IRule接口可以自定义负载策略，主要的选择服务逻辑在choose方法中。
实现基于Nacos权重的负载均衡策略：
package com.morris.user.config;import com.alibaba.cloud.nacos.NacosDiscoveryProperties;import com.alibaba.cloud.nacos.NacosServiceManager;import com.alibaba.cloud.nacos.ribbon.NacosServer;import com.alibaba.nacos.api.exception.NacosException;import com.alibaba.nacos.api.naming.NamingService;import com.alibaba.nacos.api.naming.pojo.Instance;import com.netflix.client.config.IClientConfig;import com.netflix.loadbalancer.AbstractLoadBalancerRule;import com.netflix.loadbalancer.DynamicServerListLoadBalancer;import com.netflix.loadbalancer.Server;import lombok.extern.slf4j.Slf4j;import javax.annotation.Resource;@Slf4jpublic class NacosRandomWithWeightRule extends AbstractLoadBalancerRule {@Resourceprivate NacosServiceManager nacosServiceManager;@Resourceprivate NacosDiscoveryProperties nacosDiscoveryProperties;@Overridepublic Server choose(Object key) {DynamicServerListLoadBalancer loadBalancer = (DynamicServerListLoadBalancer) getLoadBalancer();String serviceName = loadBalancer.getName();NamingService namingService = nacosServiceManager.getNamingService(nacosDiscoveryProperties.getNacosProperties());try {//nacos基于权重的算法Instance instance = namingService.selectOneHealthyInstance(serviceName);return new NacosServer(instance);} catch (NacosException e) {log.error("获取服务实例异常：{}", e.getMessage());e.printStackTrace();}return null;}@Overridepublic void initWithNiwsConfig(IClientConfig iClientConfig) {}}可以将NacosRandomWithWeightRule按照上面的全局配置或者局部配置。
饥饿加载在进行服务调用的时候，如果网络情况不好，第一次调用会超时。Ribbon默认懒加载，意味着只有在发起调用的时候才会创建客户端。
应用启动后第一次请求会有2s左右的延时，如果此时有大量请求进来就会抛出大量异常。
2023-07-21 16:50:37.718 INFO 20488 --- [nio-8030-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring DispatcherServlet 'dispatcherServlet'2023-07-21 16:50:37.718 INFO 20488 --- [nio-8030-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'2023-07-21 16:50:37.733 INFO 20488 --- [nio-8030-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 15 ms2023-07-21 16:50:39.332 INFO 20488 --- [nio-8030-exec-1] c.netflix.loadbalancer.BaseLoadBalancer : Client: order-service instantiated a LoadBalancer: DynamicServerListLoadBalancer:{NFLoadBalancer:name=order-service,current list of Servers=[],Load balancer stats=Zone stats: {},Server stats: []}ServerList:null2023-07-21 16:50:39.346 INFO 20488 --- [nio-8030-exec-1] c.n.l.DynamicServerListLoadBalancer : Using serverListUpdater PollingServerListUpdater2023-07-21 16:50:39.534 INFO 20488 --- [nio-8030-exec-1] c.n.l.DynamicServerListLoadBalancer : DynamicServerListLoadBalancer for client order-service initialized: DynamicServerListLoadBalancer:{NFLoadBalancer:name=order-service,current list of Servers=[2.0.0.1:8020],Load balancer stats=Zone stats: {unknown=[Zone:unknown;Instance count:1;Active connections count: 0;Circuit breaker tripped count: 0;Active connections per server: 0.0;]},Server stats: [[Server:2.0.0.1:8020;Zone:UNKNOWN;Total Requests:0;Successive connection failure:0;Total blackout seconds:0;Last connection made:Thu Jan 01 08:00:00 CST 1970;First connection made: Thu Jan 01 08:00:00 CST 1970;Active Connections:0;total failure count in last (1000) msecs:0;average resp time:0.0;90 percentile resp time:0.0;95 percentile resp time:0.0;min resp time:0.0;max resp time:0.0;stddev resp time:0.0]]}ServerList:com.alibaba.cloud.nacos.ribbon.NacosServerList@fb090e开启饥饿加载，解决第一次调用慢的问题：
ribbon:eager-load:enabled: trueclients: order-service参数说明：
ribbon.eager-load.enabled：开启ribbon的饥饿加载模式ribbon.eager-load.clients：指定需要饥饿加载的服务名，也就是你需要调用的服务，如果有多个服务，则用逗号隔开看下效果，在启动过程中就已经初始化连接了：
2023-07-21 16:54:18.480 INFO 22040 --- [ main] com.morris.user.UserServiceApplication : Started UserServiceApplication in 6.846 seconds (JVM running for 8.265)2023-07-21 16:54:19.254 INFO 22040 --- [ main] c.netflix.loadbalancer.BaseLoadBalancer : Client: order-service instantiated a LoadBalancer: DynamicServerListLoadBalancer:{NFLoadBalancer:name=order-service,current list of Servers=[],Load balancer stats=Zone stats: {},Server stats: []}ServerList:null2023-07-21 16:54:19.260 INFO 22040 --- [ main] c.n.l.DynamicServerListLoadBalancer : Using serverListUpdater PollingServerListUpdater2023-07-21 16:54:19.286 INFO 22040 --- [ main] c.n.l.DynamicServerListLoadBalancer : DynamicServerListLoadBalancer for client order-service initialized: DynamicServerListLoadBalancer:{NFLoadBalancer:name=order-service,current list of Servers=[2.0.0.1:8020],Load balancer stats=Zone stats: {unknown=[Zone:unknown;Instance count:1;Active connections count: 0;Circuit breaker tripped count: 0;Active connections per server: 0.0;]},Server stats: [[Server:2.0.0.1:8020;Zone:UNKNOWN;Total Requests:0;Successive connection failure:0;Total blackout seconds:0;Last connection made:Thu Jan 01 08:00:00 CST 1970;First connection made: Thu Jan 01 08:00:00 CST 1970;Active Connections:0;total failure count in last (1000) msecs:0;average resp time:0.0;90 percentile resp time:0.0;95 percentile resp time:0.0;min resp time:0.0;max resp time:0.0;stddev resp time:0.0]]}ServerList:com.alibaba.cloud.nacos.ribbon.NacosServerList@432469 NacosRule源码分析com.alibaba.cloud.nacos.ribbon.NacosRule#choose
@Overridepublic Server choose(Object key) {try {String clusterName = this.nacosDiscoveryProperties.getClusterName();String group = this.nacosDiscoveryProperties.getGroup();DynamicServerListLoadBalancer loadBalancer = (DynamicServerListLoadBalancer) getLoadBalancer();String name = loadBalancer.getName();// 获取NamingService，在我们的代码中也可以这么使用NamingService namingService = nacosServiceManager.getNamingService(nacosDiscoveryProperties.getNacosProperties());// 筛选出同一个group的实例，不同group之间不能通讯List<Instance> instances = namingService.selectInstances(name, group, true);if (CollectionUtils.isEmpty(instances)) {LOGGER.warn("no instance in service {}", name);return null;}List<Instance> instancesToChoose = instances;if (StringUtils.isNotBlank(clusterName)) {// 找出同一个集群的节点List<Instance> sameClusterInstances = instances.stream().filter(instance -> Objects.equals(clusterName,instance.getClusterName())).collect(Collectors.toList());if (!CollectionUtils.isEmpty(sameClusterInstances)) {instancesToChoose = sameClusterInstances;}else {LOGGER.warn("A cross-cluster call occurs，name = {}, clusterName = {}, instance = {}",name, clusterName, instances);}}// 带权重的随机选择一个节点Instance instance = ExtendBalancer.getHostByRandomWeight2(instancesToChoose);return new NacosServer(instance);}catch (Exception e) {LOGGER.warn("NacosRule error", e);return null;}}NacosRule是AlibabaNacos自己实现的一个负载均衡策略，可以在nacos平台中根据自定义权重进行访问。
基于Nacos元数据的版本控制自定义负载均衡实际项目，我们可能还会有这样的需求：
一个微服务在线上可能多版本共存，且多个版本的微服务并不兼容。使用Nacos的自定义元数据，可以实现微服务的版本控制。
配置文件的格式： spring.cloud.nacos.discovery.metadata.{key}={value}
当前配置的版本： spring.cloud.nacos.discovery.metadata.version=V1
package com.morris.user.config;import com.alibaba.cloud.nacos.NacosDiscoveryProperties;import com.alibaba.cloud.nacos.NacosServiceManager;import com.alibaba.cloud.nacos.ribbon.ExtendBalancer;import com.alibaba.cloud.nacos.ribbon.NacosServer;import com.alibaba.nacos.api.exception.NacosException;import com.alibaba.nacos.api.naming.NamingService;import com.alibaba.nacos.api.naming.pojo.Instance;import com.netflix.client.config.IClientConfig;import com.netflix.loadbalancer.AbstractLoadBalancerRule;import com.netflix.loadbalancer.BaseLoadBalancer;import com.netflix.loadbalancer.Server;import lombok.extern.slf4j.Slf4j;import org.apache.commons.lang.StringUtils;import javax.annotation.Resource;import java.util.List;import java.util.stream.Collectors;@Slf4jpublic class ClusterMetaDataRibbonRule extends AbstractLoadBalancerRule {@Resourceprivate NacosDiscoveryProperties nacosDiscoveryProperties;@Resourceprivate NacosServiceManager nacosServiceManager;@Overridepublic void initWithNiwsConfig(IClientConfig iClientConfig) {}@Overridepublic Server choose(Object o) {log.info("-------key: {}", o);// 获取当前服务的集群名称String currentClusterName = nacosDiscoveryProperties.getClusterName();// 获取当前版本String currentVersion = nacosDiscoveryProperties.getMetadata().get("version");// 获取被调用的服务的名称BaseLoadBalancer baseLoadBalancer = (BaseLoadBalancer) getLoadBalancer();String serviceName = baseLoadBalancer.getName();// 获取nacos clinet的服务注册发现组件的apiNamingService namingService = nacosServiceManager.getNamingService(nacosDiscoveryProperties.getNacosProperties());try {// 获取所有被调用服务List<Instance> allInstances = namingService.getAllInstances(serviceName);// 过滤出相同版本且相同集群下的所有服务List<Instance> sameVersionAndClusterInstances = allInstances.stream().filter(x -> StringUtils.equalsIgnoreCase(x.getMetadata().get("version"), currentVersion)&& StringUtils.equalsIgnoreCase(x.getClusterName(), currentClusterName)).collect(Collectors.toList());Instance chooseInstance;if(sameVersionAndClusterInstances.isEmpty()) {// 过滤出所有相同版本的服务List<Instance> sameVersionInstances = allInstances.stream().filter(x -> StringUtils.equalsIgnoreCase(x.getMetadata().get("version"), currentVersion)).collect(Collectors.toList());if(sameVersionInstances.isEmpty()) {log.info("跨集群调用找不到对应合适的版本当前版本为:currentVersion:{}",currentVersion);throw new RuntimeException("找不到相同版本的微服务实例");}else {// 随机权重chooseInstance = ExtendBalancer.getHostByRandomWeight2(sameVersionInstances);log.info("跨集群同版本调用--->当前微服务所在集群:{},被调用微服务所在集群:{},当前微服务的版本:{},被调用微服务版本:{},Host:{},Port:{}",currentClusterName, chooseInstance.getClusterName(), chooseInstance.getMetadata().get("current-version"),chooseInstance.getMetadata().get("current-version"), chooseInstance.getIp(), chooseInstance.getPort());}}else {chooseInstance = ExtendBalancer.getHostByRandomWeight2(sameVersionAndClusterInstances);log.info("同集群同版本调用--->当前微服务所在集群:{},被调用微服务所在集群:{},当前微服务的版本:{},被调用微服务版本:{},Host:{},Port:{}",currentClusterName, chooseInstance.getClusterName(), chooseInstance.getMetadata().get("version"),chooseInstance.getMetadata().get("current-version"), chooseInstance.getIp(), chooseInstance.getPort());}return new NacosServer(chooseInstance);} catch (NacosException e) {log.error("error,", e);return null;}}}
