Major we encountered a problem when new connections ceased to be established, while the old ones worked correctly, the connection of new agents ended with a message at the bottom.
The following was applied to solve and restore working efficiency: I turned off the JNLPby selecting Disable, then applied the configuration, after re-entering the settings I again set the previously configured port number (the port number did not change) and the new connections started working correctly, the old ones were not disconnected and build tasks continued to work.
The master did not reboot, it was possible to fix it without downtime, however this is not normal behavior of the services processing the JNLP
INFO: Agent discovery successful
Agent address: sbt-jenkins.ca.sbrf.ru
Agent port: 8186
Identity: ba:bd:6b:f0:59:5f:c4:b8:26:2a:c0:5d:18:d0:9d:e9
╨╕╤О╨╜ 02, 2020 11:43:50 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Handshaking
╨╕╤О╨╜ 02, 2020 11:43:50 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to sbt-jenkins.ca.sbrf.ru:8186
╨╕╤О╨╜ 02, 2020 11:43:50 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Trying protocol: JNLP4-connect
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Protocol JNLP4-connect encountered an unexpected exception java.util.concurrent.ExecutionException: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent
at org.jenkinsci.remoting.util.SettableFuture.get(SettableFuture.java:223)
at hudson.remoting.Engine.innerRun(Engine.java:614)
at hudson.remoting.Engine.run(Engine.java:474)
Caused by: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent
at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.onRecvClosed(AckFilterLayer.java:280)
at org.jenkinsci.remoting.protocol.ProtocolStack$Ptr.onRecvClosed(ProtocolStack.java:816)
at org.jenkinsci.remoting.protocol.FilterLayer.onRecvClosed(FilterLayer.java:287)
at org.jenkinsci.remoting.protocol.ProtocolStack$Ptr.onRecvClosed(ProtocolStack.java:816)
at org.jenkinsci.remoting.protocol.NetworkLayer.onRecvClosed(NetworkLayer.java:154)
at org.jenkinsci.remoting.protocol.impl.BIONetworkLayer.access$1500(BIONetworkLayer.java:48)
at org.jenkinsci.remoting.protocol.impl.BIONetworkLayer$Reader.run(BIONetworkLayer.java:247)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at hudson.remoting.Engine$1.lambda$newThread$0(Engine.java:93)
at java.lang.Thread.run(Thread.java:748)╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to sbt-jenkins.ca.sbrf.ru:8186
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server reports protocol JNLP4-plaintext not supported, skipping
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server reports protocol JNLP3-connect not supported, skipping
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server reports protocol JNLP2-connect not supported, skipping
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener status
INFO: Server reports protocol JNLP-connect not supported, skipping
╨╕╤О╨╜ 02, 2020 11:43:51 AM hudson.remoting.jnlp.Main$CuiListener error
SEVERE: The server rejected the connection: None of the protocols were accepted java.lang.Exception: The server rejected the connection: None of the protocols were accepted
at hudson.remoting.Engine.onConnectionRejected(Engine.java:682)
at hudson.remoting.Engine.innerRun(Engine.java:639)
at hudson.remoting.Engine.run(Engine.java:474)
