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Feign 本质上是一个 HTTP 客户端，用于简化微服务之间的 HTTP 通信。它允许开发者通过定义接口和注解来声明式地编写 HTTP 客户端，而无需手动编写 HTTP 请求和响应处理的代码。
今天在模拟微服务A feign调用微服务B的时候，把微服务B关了，可是调用的时候不会走fallback降级方法。直接报错：
2024-09-28 18:45:00.247 ERROR 13248 --- [illProductJob-2] c.d.d.j.e.h.i.DefaultJobExceptionHandler : Job 'InitSeckillProductJob' exception occur in job processingjava.lang.RuntimeException: com.netflix.client.ClientException: Load balancer does not have available server for client: seckill-serviceat org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient.execute(LoadBalancerFeignClient.java:90) ~[spring-cloud-openfeign-core-2.2.5.RELEASE.jar:2.2.5.RELEASE]at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:119) ~[feign-core-10.10.1.jar:na]at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:89) ~[feign-core-10.10.1.jar:na]at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:100) ~[feign-core-10.10.1.jar:na]at com.sun.proxy.$Proxy76.queryByTimeForJob(Unknown Source) ~[na:na]at cn.dscode.job.InitSeckillProductJob.execute(InitSeckillProductJob.java:38) ~[classes/:na]at com.dangdang.ddframe.job.executor.type.SimpleJobExecutor.process(SimpleJobExecutor.java:41) ~[elastic-job-common-core-2.1.5.jar:na]at com.dangdang.ddframe.job.executor.AbstractElasticJobExecutor.process(AbstractElasticJobExecutor.java:206) [elastic-job-common-core-2.1.5.jar:na]at com.dangdang.ddframe.job.executor.AbstractElasticJobExecutor.access$000(AbstractElasticJobExecutor.java:47) [elastic-job-common-core-2.1.5.jar:na]at com.dangdang.ddframe.job.executor.AbstractElasticJobExecutor$1.run(AbstractElasticJobExecutor.java:185) [elastic-job-common-core-2.1.5.jar:na]at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_422]at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266) [na:1.8.0_422]at java.util.concurrent.FutureTask.run(FutureTask.java) [na:1.8.0_422]at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_422]at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_422]at java.lang.Thread.run(Thread.java:750) [na:1.8.0_422]
Caused by: com.netflix.client.ClientException: Load balancer does not have available server for client: seckill-serviceat com.netflix.loadbalancer.LoadBalancerContext.getServerFromLoadBalancer(LoadBalancerContext.java:483) ~[ribbon-loadbalancer-2.3.0.jar:2.3.0]at com.netflix.loadbalancer.reactive.LoadBalancerCommand$1.call(LoadBalancerCommand.java:184) ~[ribbon-loadbalancer-2.3.0.jar:2.3.0]at com.netflix.loadbalancer.reactive.LoadBalancerCommand$1.call(LoadBalancerCommand.java:180) ~[ribbon-loadbalancer-2.3.0.jar:2.3.0]at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeConcatMap.call(OnSubscribeConcatMap.java:94) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeConcatMap.call(OnSubscribeConcatMap.java:42) ~[rxjava-1.3.8.jar:1.3.8]at rx.Observable.unsafeSubscribe(Observable.java:10327) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OperatorRetryWithPredicate$SourceSubscriber$1.call(OperatorRetryWithPredicate.java:127) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.schedulers.TrampolineScheduler$InnerCurrentThreadScheduler.enqueue(TrampolineScheduler.java:73) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.schedulers.TrampolineScheduler$InnerCurrentThreadScheduler.schedule(TrampolineScheduler.java:52) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OperatorRetryWithPredicate$SourceSubscriber.onNext(OperatorRetryWithPredicate.java:79) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OperatorRetryWithPredicate$SourceSubscriber.onNext(OperatorRetryWithPredicate.java:45) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.util.ScalarSynchronousObservable$WeakSingleProducer.request(ScalarSynchronousObservable.java:276) ~[rxjava-1.3.8.jar:1.3.8]at rx.Subscriber.setProducer(Subscriber.java:209) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.util.ScalarSynchronousObservable$JustOnSubscribe.call(ScalarSynchronousObservable.java:138) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.util.ScalarSynchronousObservable$JustOnSubscribe.call(ScalarSynchronousObservable.java:129) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48) ~[rxjava-1.3.8.jar:1.3.8]at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30) ~[rxjava-1.3.8.jar:1.3.8]at rx.Observable.subscribe(Observable.java:10423) ~[rxjava-1.3.8.jar:1.3.8]at rx.Observable.subscribe(Observable.java:10390) ~[rxjava-1.3.8.jar:1.3.8]at rx.observables.BlockingObservable.blockForSingle(BlockingObservable.java:443) ~[rxjava-1.3.8.jar:1.3.8]at rx.observables.BlockingObservable.single(BlockingObservable.java:340) ~[rxjava-1.3.8.jar:1.3.8]at com.netflix.client.AbstractLoadBalancerAwareClient.executeWithLoadBalancer(AbstractLoadBalancerAwareClient.java:112) ~[ribbon-loadbalancer-2.3.0.jar:2.3.0]at org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient.execute(LoadBalancerFeignClient.java:83) ~[spring-cloud-openfeign-core-2.2.5.RELEASE.jar:2.2.5.RELEASE]... 15 common frames omitted
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配置文件已经开启了Feign与Sentinel的集成，启用熔断降级
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服务A使用Feign去调用另一个服务B
降级类
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服务B
后面发现是没加sentinel依赖
<!-- sentinel组件 -->
<dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
</dependency>