IllegalStateException after read timeout

Spring Boot Admin Server information

• Version:
  3.1.6

• Spring Boot version:
  3.1.3

• Configured Security:
  no auth, service is not exposed outside

• Webflux or Servlet application:
  Webflux

Client information

• Spring Boot versions:
  3.1.3

• Used discovery mechanism:
  self registration

spring.boot.admin.client.url: ...
spring.boot.admin.client.instance.service-host-type: ip

• Webflux or Servlet application:
  Servlet

Description

Following exception is observed:

[registrationTask1] WARN d.c.b.a.c.r.ApplicationRegistrator@register:91 - Failed to register application as Application(name=Agent-Registration-Handler, managementUrl=http://10.0.42.76:8081/actuator, healthUrl=http://10.0.42.76:8081/actuator/health, serviceUrl=http://10.0.42.76:8080/) at spring-boot-admin ([http://application-admin-service:80/instances]): java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 5000ms in 'flatMap' (and no fallback has been configured). Further attempts are logged on DEBUG level
[reactor-http-epoll-1] ERROR reactor.core.publisher.Operators@error:324 - Operator called default onErrorDropped
java.lang.IllegalStateException: The client response body has been released already due to cancellation.
	at org.springframework.http.client.reactive.ReactorClientHttpResponse.lambda$getBody$0(ReactorClientHttpResponse.java:117)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onSubscribe(FluxPeek.java:162)
	at reactor.core.publisher.FluxMap$MapSubscriber.onSubscribe(FluxMap.java:92)
	at reactor.netty.channel.FluxReceive.startReceiver(FluxReceive.java:170)
	at reactor.netty.channel.FluxReceive.subscribe(FluxReceive.java:145)
	at reactor.core.publisher.InternalFluxOperator.subscribe(InternalFluxOperator.java:62)
	at reactor.netty.ByteBufFlux.subscribe(ByteBufFlux.java:340)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:55)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:165)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
	at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:113)
	at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:180)
	at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:854)
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74)
	at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onNext(FluxOnAssembly.java:539)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:200)
	at reactor.core.publisher.FluxMap$MapSubscriber.onNext(FluxMap.java:122)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:79)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:200)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:200)
	at reactor.core.publisher.FluxPeek$PeekSubscriber.onNext(FluxPeek.java:200)
	at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82)
	at reactor.core.publisher.MonoFlatMapMany$FlatMapManyInner.onNext(MonoFlatMapMany.java:250)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2545)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.request(FluxContextWrite.java:136)
	at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onSubscribeInner(MonoFlatMapMany.java:150)
	at reactor.core.publisher.MonoFlatMapMany$FlatMapManyInner.onSubscribe(MonoFlatMapMany.java:245)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onSubscribe(FluxContextWrite.java:101)
	at reactor.core.publisher.FluxJust.subscribe(FluxJust.java:68)
	at reactor.core.publisher.Flux.subscribe(Flux.java:8773)
	at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onNext(MonoFlatMapMany.java:195)
	at reactor.core.publisher.SerializedSubscriber.onNext(SerializedSubscriber.java:99)
	at reactor.core.publisher.FluxRetryWhen$RetryWhenMainSubscriber.onNext(FluxRetryWhen.java:174)
	at reactor.core.publisher.MonoCreate$DefaultMonoSink.success(MonoCreate.java:172)
	at reactor.netty.http.client.HttpClientConnect$HttpIOHandlerObserver.onStateChange(HttpClientConnect.java:435)
	at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:710)
	at reactor.netty.resources.DefaultPooledConnectionProvider$DisposableAcquire.onStateChange(DefaultPooledConnectionProvider.java:195)
	at reactor.netty.resources.DefaultPooledConnectionProvider$PooledConnection.onStateChange(DefaultPooledConnectionProvider.java:456)
	at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:647)
	at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:114)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346)
	at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:333)
	at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:454)
	at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290)
	at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
	at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
	at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
	at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
	at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:800)
	at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:509)
	at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:407)
	at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
	at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:833)
[registrationTask1] INFO d.c.b.a.c.r.ApplicationRegistrator@register:82 - Application registered itself as 897a49352c41

But, as I understand, expected behaviour should be timeout exception

Start at ApplicationRegistrator.register, which the stack trace points to at lines 82 and 91, and trace the 5-second registration timeout and cancellation path. Reproduce the self-registration timeout with the listed Spring Boot 3.1.x setup; done means the timeout is reported without the released-body IllegalStateException.