本系列是 我TM人傻了 系列第六期[捂脸]，往期精彩回顾：
降级到Spring 5.3.x之后，GC次数急剧减少，我TM人傻了
这个大表走索引字段查问的 SQL 怎么就成全扫描了，我TM人傻了
获取异样信息里再出异样就找不到日志了，我TM人傻了
spring-data-redis 连贯透露，我 TM 人傻了
Spring Cloud Gateway 没有链路信息，我 TM 人傻了

大家好，我又人傻了。这次的教训通知咱们，进去写代码偷的懒，迟早要还的。

问题景象与背景

昨晚咱们的网关雪崩了一段时间，景象是：

1.一直有各种微服务报异样：在写 HTTP 响应的时候，连贯曾经敞开：

reactor.netty.http.client.PrematureCloseException: Connection prematurely closed BEFORE response

2.同时还有申请还没读取完，连贯曾经敞开的异样：

org.springframework.http.converter.HttpMessageNotReadableException: I/O error while reading input message; nested exception is java.io.IOException: UT000128: Remote peer closed connection before all data could be read

3.前端一直有申请超时的报警，504 Gateway Time-out

4.网关过程一直健康检查失败而被重启

5.重启后的网关过程，立即申请数量激增，每个实例峰值 2000 qps，闲时每个实例 500 qps，忙时因为有扩容也能放弃每个实例在 1000 qps 以内，而后健康检查接口就很长时间没有响应，导致实例一直重启

其中，1 和 2 的问题应该是应为网关一直重启，并且因为某些起因优雅敞开失败导致强制敞开，强制敞开导致连贯被强制断开从而有 1 和 2 相干的异样。

咱们的网关是基于 Spring Cloud Gateway 实现的，并且有主动依据 CPU 负载扩容的机制。奇怪的是在申请数量彪增的时候，CPU 利用率并没有进步很多，放弃在 60% 左右，因为 CPU 负载没有达到扩容的界线，所以始终没有主动扩容。为了疾速解决问题，咱们手动扩容了几个网关实例，将网关单实例负载管制在了 1000 以内，临时解决了问题。

问题剖析

为了彻底解决这个问题，咱们应用 JFR 剖析。首先先依据已知的线索去剖析：

Spring Cloud Gateway 是基于 Spring-WebFlux 实现的异步响应式网关，http 业务线程是无限的（默认是 2 * 能够应用的 CPU 个数，咱们这里是 4）。
网关过程一直健康检查失败，健康检查调用的是 /actuator/health 接口，这个接口始终超时。

健康检查接口超时个别有两个起因：

健康检查接口查看某个组件的时候，阻塞住了。例如数据库如果卡住，那么可能数据库健康检查会始终没有返回。
http 线程池没来得及解决健康检查申请，申请就超时了。

咱们能够先去看 JFR 中的定时堆栈，看是否有 http 线程卡在健康检查下面。查看出问题后的线程堆栈，重点关注那 4 个 http 线程，后果发现这 4 个线程的堆栈根本一样，都是在执行 Redis 命令：

"reactor-http-nio-1" #68 daemon prio=5 os_prio=0 cpu=70832.99ms elapsed=199.98s tid=0x0000ffffb2f8a740 nid=0x69 waiting on condition  [0x0000fffe8adfc000]   java.lang.Thread.State: TIMED_WAITING (parking)    at jdk.internal.misc.Unsafe.park(java.base@11.0.8/Native Method)    - parking to wait for  <0x00000007d50eddf8> (a java.util.concurrent.CompletableFuture$Signaller)    at java.util.concurrent.locks.LockSupport.parkNanos(java.base@11.0.8/LockSupport.java:234)    at java.util.concurrent.CompletableFuture$Signaller.block(java.base@11.0.8/CompletableFuture.java:1798)    at java.util.concurrent.ForkJoinPool.managedBlock(java.base@11.0.8/ForkJoinPool.java:3128)    at java.util.concurrent.CompletableFuture.timedGet(java.base@11.0.8/CompletableFuture.java:1868)    at java.util.concurrent.CompletableFuture.get(java.base@11.0.8/CompletableFuture.java:2021)    at io.lettuce.core.protocol.AsyncCommand.await(AsyncCommand.java:83)    at io.lettuce.core.internal.Futures.awaitOrCancel(Futures.java:244)    at io.lettuce.core.FutureSyncInvocationHandler.handleInvocation(FutureSyncInvocationHandler.java:75)    at io.lettuce.core.internal.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:80)    at com.sun.proxy.$Proxy245.get(Unknown Source)    at org.springframework.data.redis.connection.lettuce.LettuceStringCommands.get(LettuceStringCommands.java:68)    at org.springframework.data.redis.connection.DefaultedRedisConnection.get(DefaultedRedisConnection.java:267)    at org.springframework.data.redis.connection.DefaultStringRedisConnection.get(DefaultStringRedisConnection.java:406)    at org.springframework.data.redis.core.DefaultValueOperations$1.inRedis(DefaultValueOperations.java:57)    at org.springframework.data.redis.core.AbstractOperations$ValueDeserializingRedisCallback.doInRedis(AbstractOperations.java:60)    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:222)    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:189)    at org.springframework.data.redis.core.AbstractOperations.execute(AbstractOperations.java:96)    at org.springframework.data.redis.core.DefaultValueOperations.get(DefaultValueOperations.java:53)    at com.jojotech.apigateway.filter.AccessCheckFilter.traced(AccessCheckFilter.java:196)    at com.jojotech.apigateway.filter.AbstractTracedFilter.filter(AbstractTracedFilter.java:39)    at org.springframework.cloud.gateway.handler.FilteringWebHandler$GatewayFilterAdapter.filter(FilteringWebHandler.java:137)    at org.springframework.cloud.gateway.filter.OrderedGatewayFilter.filter(OrderedGatewayFilter.java:44)    at org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain.lambda$filter$0(FilteringWebHandler.java:117)    at org.springframework.cloud.gateway.handler.FilteringWebHandler$DefaultGatewayFilterChain$$Lambda$1478/0x0000000800b84c40.get(Unknown Source)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at com.jojotech.apigateway.common.TracedMono.subscribe(TracedMono.java:24)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:255)    at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)    at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:157)    at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:73)    at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:281)    at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:860)    at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:120)    at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:73)    at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1815)    at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:151)    at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:120)    at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:281)    at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:860)    at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:79)    at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:180)    at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1815)    at reactor.core.publisher.MonoFilterWhen$MonoFilterWhenMain.onNext(MonoFilterWhen.java:149)    at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2397)    at reactor.core.publisher.MonoFilterWhen$MonoFilterWhenMain.onSubscribe(MonoFilterWhen.java:112)    at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:448)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onNext(FluxConcatMap.java:250)    at reactor.core.publisher.FluxDematerialize$DematerializeSubscriber.onNext(FluxDematerialize.java:98)    at reactor.core.publisher.FluxDematerialize$DematerializeSubscriber.onNext(FluxDematerialize.java:44)    at reactor.core.publisher.FluxIterable$IterableSubscription.slowPath(FluxIterable.java:270)    at reactor.core.publisher.FluxIterable$IterableSubscription.request(FluxIterable.java:228)    at reactor.core.publisher.FluxDematerialize$DematerializeSubscriber.request(FluxDematerialize.java:127)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:235)    at reactor.core.publisher.FluxDematerialize$DematerializeSubscriber.onSubscribe(FluxDematerialize.java:77)    at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:164)    at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:86)    at reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:62)    at reactor.core.publisher.FluxDefer.subscribe(FluxDefer.java:54)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:448)    at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:218)    at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:164)    at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:86)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at org.springframework.cloud.sleuth.instrument.web.TraceWebFilter$MonoWebFilterTrace.subscribe(TraceWebFilter.java:184)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)    at reactor.core.publisher.Mono.subscribe(Mono.java:4150)    at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:255)    at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)    at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)    at reactor.netty.http.server.HttpServer$HttpServerHandle.onStateChange(HttpServer.java:915)    at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:654)    at reactor.netty.transport.ServerTransport$ChildObserver.onStateChange(ServerTransport.java:478)    at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:526)    at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:94)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)    at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:209)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)    at reactor.netty.http.server.logging.AccessLogHandlerH1.channelRead(AccessLogHandlerH1.java:59)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)    at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324)    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296)    at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357)    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:719)    at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)    at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)    at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)    at java.lang.Thread.run(java.base@11.0.8/Thread.java:834)

发现 http 线程没有卡在健康检查，同时其余线程也没有任何和健康检查相干的堆栈（异步环境下，健康检查也是异步的，其中某些过程可能交给其余线程）。所以，健康检查申请应该是还没被执行就超时勾销了。

那么为啥会这样呢？于此同时，我还发现这里用的是 RedisTemplate，是 spring-data-redis 的同步 Redis API。我猛然想起来之前写这里的代码的时候，因为只是验证一个 key 是否存在和批改 key 的过期工夫，偷懒没有用异步 API。这里是不是因为应用同步 API 阻塞了 http 线程导致的雪崩呢？

咱们来验证下这个猜测：咱们的我的项目中 redis 操作是通过 spring-data-redis + Lettuce 连接池，启用并且减少了对于 Lettuce 命令的 JFR 监控，能够参考我的这篇文章：这个 Redis 连接池的新监控形式针不戳~我再加一点佐料，截至目前我的 pull request 曾经合并，这个个性会在 6.2.x 版本公布。咱们看下出问题工夫左近的 Redis 命令采集，如下图所示：

咱们来简略计算下执行 Redis 命令导致的阻塞工夫（咱们的采集是 10s 一次，count 是命令次数，工夫单位是微秒）：应用这里的命令个数乘以 50% 的中位数，除以 10（因为是 10s），得出每秒因为执行 Redis 命令导致的阻塞工夫：

32*152=48641*860=8605*163=81532*176=56321*178=17816959*168=2849112774*176=1362243144*166=52190417343*179=3104397702*166=116532总和 67405186740518 / 10 = 674051.8 us = 0.67s

这个仅仅是应用中位数计算的阻塞工夫，从图上的散布其实能够看出真正的值应该比这个大，这样很有可能每秒须要在 Redis 同步接口上阻塞的工夫就超过了 1s，一直地申请，申请没有缩小，从而导致了申请越积越多，最初雪崩。

并且因为是阻塞接口，线程很多工夫耗费在期待 io 了，所以 CPU 上不去，导致没有主动扩容。业务顶峰时，因为有设定好的事后扩容，导致网关单实例没有达到出问题的压力，所以没问题。

解决问题

咱们来改写原有代码，应用同步 spring-data-redis Api 原有代码是(其实就是 spring-cloud-gateway 的 Filter 接口的外围办法 public Mono<Void> traced(ServerWebExchange exchange, GatewayFilterChain chain) 的办法体)：

if (StringUtils.isBlank(token)) {    //如果 token 不存在，则依据门路决定持续申请还是返回须要登录的状态码    return continueOrUnauthorized(path, exchange, chain, headers);} else {    try {        String accessTokenValue = redisTemplate.opsForValue().get(token);        if (StringUtils.isNotBlank(accessTokenValue)) {            //如果 accessTokenValue 不为空，则续期 4 小时，保障登录用户只有有操作就不会让 token 过期            Long expire = redisTemplate.getExpire(token);            log.info("accessTokenValue = {}, expire = {}", accessTokenValue, expire);            if (expire != null && expire < 4 * 60 * 60) {                redisTemplate.expire(token, 4, TimeUnit.HOURS);            }                        //解析，获取 userId            JSONObject accessToken = JSON.parseObject(accessTokenValue);            String userId = accessToken.getString("userId");            //如果 userId 不为空才非法            if (StringUtils.isNotBlank(userId)) {                //解析 Token                 HttpHeaders newHeaders = parse(accessToken);                //持续申请                return FilterUtil.changeRequestHeader(exchange, chain, newHeaders);            }        }    } catch (Exception e) {        log.error("read accessToken error: {}", e.getMessage(), e);    }    //如果 token 不非法，则依据门路决定持续申请还是返回须要登录的状态码    return continueOrUnauthorized(path, exchange, chain, headers);}

改成应用异步：

if (StringUtils.isBlank(token)) {    return continueOrUnauthorized(path, exchange, chain, headers);} else {    HttpHeaders finalHeaders = headers;    //必须应用 tracedPublisherFactory 包裹，否则链路信息会失落，这里参考我的另一篇文章：Spring Cloud Gateway 没有链路信息，我 TM 人傻了    return tracedPublisherFactory.getTracedMono(            redisTemplate.opsForValue().get(token)                    //必须切换线程，否则后续线程应用的还是 Redisson 的线程，如果耗时长则会影响其余应用 Redis 的业务，并且这个耗时也算在 Redis 连贯命令超时中                    .publishOn(Schedulers.parallel()),            exchange    ).doOnSuccess(accessTokenValue -> {        if (accessTokenValue != null) {            //accessToken续期,4小时            tracedPublisherFactory.getTracedMono(redisTemplate.getExpire(token).publishOn(Schedulers.parallel()), exchange).doOnSuccess(expire -> {                log.info("accessTokenValue = {}, expire = {}", accessTokenValue, expire);                if (expire != null && expire.toHours() < 4) {                    redisTemplate.expire(token, Duration.ofHours(4)).subscribe();                }            }).subscribe();        }    })    //必须转换成非 null，否则 flatmap 不会执行；也不能在开端用 switchIfEmpty，因为整体返回的是 Mono<Void> 原本外面承载的就是空的，会导致每个申请发送两遍。    .defaultIfEmpty("")    .flatMap(accessTokenValue -> {        try {            if (StringUtils.isNotBlank(accessTokenValue)) {                JSONObject accessToken = JSON.parseObject(accessTokenValue);                String userId = accessToken.getString("userId");                if (StringUtils.isNotBlank(userId)) {                    //解析 Token                     HttpHeaders newHeaders = parse(accessToken);                    //持续申请                    return FilterUtil.changeRequestHeader(exchange, chain, newHeaders);                }            }            return continueOrUnauthorized(path, exchange, chain, finalHeaders);        } catch (Exception e) {            log.error("read accessToken error: {}", e.getMessage(), e);            return continueOrUnauthorized(path, exchange, chain, finalHeaders);        }    });}

这里有几个留神点：

Spring-Cloud-Sleuth 对于 Spring-WebFlux 中做的链路追踪优先，如果咱们在 Filter 中创立新的 Flux 或者 Mono，这外面是没有链路信息的，须要咱们手动退出。这个能够参考我的另一篇文章：Spring Cloud Gateway 没有链路信息，我 TM 人傻了
spring-data-redis + Lettuce 连接池的组合，对于异步接口，咱们最好在获取响应之后切换成别的线程池执行，否则后续线程应用的还是 Redisson 的线程，如果耗时长则会影响其余应用 Redis 的业务，并且这个耗时也算在 Redis 连贯命令超时中
Project Reactor 如果两头后果有 null 值，则前面的 flatmap、map 等流操作就不执行了。如果在这里终止，前端收到的响应是有问题的。所以两头后果咱们要在每一步思考 null 问题。
spring-cloud-gateway 的外围 GatewayFilter 接口，外围办法返回的是 Mono<Void>。Mono<Void> 原本外面承载的就是空的，导致咱们不能应用开端的 switchIfEmpty 来简化两头步骤的 null，如果用了会导致每个申请发送两遍。

这样批改后，压测了下网关，单实例 2w qps 申请也没有呈现这个问题了。

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