How to avoid CheckpointOpenResourceException for Spring Boot application with Netty Server and Client

Question

I'm experimenting with Coordinated Restore at Checkpoint (CRac) and an Spring Boot application (version 3.2.2) with Spring WebFlux containing a reactive web client (all Netty) using Azul 21.0.2.

When starting the app via java -Dspring.context.checkpoint=onRefresh -XX:CRaCCheckpointTo=./crac -jar my-app.jar there are several open file descriptors from native code: timerfd, eventfd and eventpoll.

I'm suspecting Netty to hold this open files, but I'm using a bunch of other libs (mainly Spring Data Redis Reactive with Lettuce, Spring Kafka, Spring GraphQL) and I'm using Kotlin Coroutines.

Any advice? Is this a bug in Spring Webflux or Spring Data Redis Lettuce (all using Netty) or something completely different?

I'm expecting a checkpoint written to crac directory, but I get the follwing exception.

17:01:11.144 7742 ERROR main o.s.boot.SpringApplication - Application run failed

org.springframework.context.ApplicationContextException: Failed to take CRaC checkpoint on refresh
        at org.springframework.context.support.DefaultLifecycleProcessor$CracDelegate.checkpointRestore(DefaultLifecycleProcessor.java:534) ~[spring-context-6.1.3.jar!/:6.1.3]
        ...
Caused by: org.crac.CheckpointException: null
        at org.crac.Core$Compat.checkpointRestore(Core.java:144) ~[crac-1.4.0.jar!/:na]
        at org.crac.Core.checkpointRestore(Core.java:237) ~[crac-1.4.0.jar!/:na]
        at org.springframework.context.support.DefaultLifecycleProcessor$CracDelegate.checkpointRestore(DefaultLifecycleProcessor.java:528) ~[spring-context-6.1.3.jar!/:6.1.3]
        ... 15 common frames omitted
        Suppressed: jdk.internal.crac.mirror.impl.CheckpointOpenResourceException: FD fd=6 type=unknown path=anon_inode:[eventpoll]
                ... 17 common frames omitted
        Suppressed: jdk.internal.crac.mirror.impl.CheckpointOpenResourceException: FD fd=7 type=unknown path=anon_inode:[eventfd]
                ... 17 common frames omitted
        Suppressed: jdk.internal.crac.mirror.impl.CheckpointOpenResourceException: FD fd=10 type=unknown path=anon_inode:[timerfd]
                ... 17 common frames omitted
        ...

Edit: I can now confirm that this problem is related to Netty as I completly removed the Netty code and the checkpoint works without it.

Edit: There seems to be a problem if using Webflux as Server and using WebClient at the same time.