Jenkins JNLP4-connect error: "Connection closed before acknowledgement sent" FIRST ATTEMPT ONLY

Question

When trying to connect my Windows (7, 10, Server 2016) node machines to Jenkins, I get the following error:

INFO: Trying protocol: JNLP4-connect
INFO: Protocol JNLP4-connect encountered an unexpected exception
java.util.concurrent.ExecutionException: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent

But this only happens on the first connection attempt. When I immediately rerun the same command, it connects as expected.

This only started happening when we switched to the JNLP4 protocol.

I've searched around, but nothing specifically mentions only failing to connect on the first attempt:

• I found this question on the Jenkins site but the asker fixed the problem by turning off a network proxy. If that was my problem, the nodes wouldn't ever be able to connect.

• This Stack Overflow question is similar, but I don't get the WARNING: Incorrect acknowledgement sequence message. It also doesn't indicate that the error only happens on the first attempt.

Any ideas how to get the nodes to connect on the first attempt?

Answer 1

I never did figure out how to fix the problem. The workaround was to modify the batch file that calls the Java connection program into a loop that keeps trying to connect until successful.