We have a Spring Boot application that exposes a set of actuators (standard: info, health, metrics and prometheus), which are secured with basic auth, for which we have two users that get injected. Two actuators are actively used - health every 5 min and prometheus every 20 sec. This app was running success with Spring Boot 2.7.9. Since we updated to Spring Boot 3.0.3 this app is logging a NoSuchElementException every few hours:

ERROR reactor.core.publisher.Operators Operator called default onErrorDropped java.util.NoSuchElementException: null at java.base/java.util.Arrays$ArrayItr.next(Unknown Source) at org.springframework.security.web.server.ObservationWebFilterChainDecorator$AroundWebFilterObservation$SimpleAroundWebFilterObservation.start(ObservationWebFilterChainDecorator.java:274) at reactor.core.publisher.FluxPeekFuseable$PeekFuseableConditionalSubscriber.cancel(FluxPeekFuseable.java:445) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.cancel(MonoIgnoreThen.java:143) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.FluxMap$MapSubscriber.cancel(FluxMap.java:169) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:199) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:199) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:207) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.cancel(MonoIgnoreThen.java:143) at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.cancel(FluxContextWrite.java:141) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:207) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:207) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.cancel(FluxContextWrite.java:141) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.cancel(FluxContextWrite.java:141) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxPeekFuseable$PeekFuseableConditionalSubscriber.cancel(FluxPeekFuseable.java:452) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:207) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.MonoFlatMap$FlatMapMain.cancel(MonoFlatMap.java:207) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.FluxDoOnEach$DoOnEachSubscriber.cancel(FluxDoOnEach.java:113) at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.cancel(FluxPeekFuseable.java:798) at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.cancel(FluxContextWrite.java:141) at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.cancel(FluxOnAssembly.java:654) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drainLoop(Operators.java:2399) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.drain(Operators.java:2367) at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.cancel(Operators.java:2179) at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.cancel(MonoIgnoreThen.java:143) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.cancel(MonoPeekTerminal.java:144) at reactor.core.publisher.Operators.terminate(Operators.java:1277) at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:481) at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:174) at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:167) at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470) at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:403) 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(Unknown Source)

Comment From: jzheaux

Hi, @dietzsch, thanks for the report. I've pushed a fix to 6.0.x and main. The SNAPSHOT should be available momentarily. If possible, it would be nice if you could try it out and see if the issue is alleviated.

Comment From: dietzsch

Thx a lot, will give it a try asap.