STOMP broker relay only allows up to 15 client connections [SPR-16626]

[spring-projects-issues]

Stephen Franklin opened SPR-16626 and commented

I'm using Spring Messaging and Websocket to connect to RabbitMQ. I'm only able to make 15 client websocket connections to RabbitMQ, plus one system connection. Attempting to connect more than 15 clients times out after 45 seconds with the following exception:

ERROR 20500 --- [ient-loop-nio-4] o.s.m.s.s.StompBrokerRelayMessageHandler : TCP connection failure in session f: Failed to connect: Acquire operation took longer then configured maximum time

java.util.concurrent.TimeoutException: Acquire operation took longer then configured maximum time
at io.netty.channel.pool.FixedChannelPool.<init>(...)(Unknown Source) ~[netty-transport-4.1.21.Final.jar:4.1.21.Final]

This can be reproduced using the websocket guide at https://spring.io/guides/gs/messaging-stomp-websocket/ by configuring the stomp broker relay to connect to an external broker and attempting to connect more than 15 times.

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Affects: 5.0.4

[spring-projects-issues]

Rossen Stoyanchev commented

Indeed, after the switch to Reactor 3.x in Spring Framework 5, we're using a fixed connection pool too that's small if many clients try to connect at the same time. I switched to an elastic strategy and confirmed that can sustain higher concurrency.

We're expecting to release on Tuesday, March 27th. In the mean time, you can try with 5.0.5.BUILD-SNAPSHOT.

There is also a way to configure ReactorNettyTcpClient with the elastic pool yourself, and then use the tcpClient property on StompBrokerRelayMessageHandler but the fix should be released soon enough.