Jenkins Slave Connection Timeout When Connecting

Question

Last week I set up a selenium grid using Jenkins and 4 slave windows VMs. As part of doing this I had to unblock ports for both the slave connection and the selenium connection.

The VMs downloaded the JNLP starter and registered correctly and by the end of the day Friday I had my tests running as reported as expected.\

Happy Monday, I come in to find out over the weekend that the connections to all four of the VMs have been lost due to connection timeouts. (the initial error indicated it had been terminated because the ping was too long, subsequent attempts never successfully connect in the first place.)

My research on SO so far points to issues with the ports, so I checked to make sure they are still enabled, and they are. Next I restarted the Jenkins instance, and still no success.

Interestingly, the connection to the Jenkins selenium grid IS working, each of the standalone servers starts and registers correctly on the VMs, and they are all able to access the jenkins ui from the browsers, just not able to register as a slave through jnlp.

At this point I am at a loss, I've mirrored the exact same setup that was working last week. I checked with our devOps team that manages the server and verified there have been no changes on that end. The VMs have been untouched.

Answer 1

Found a solution, but it leaves at least one question.

To resolve this I altered the Jenkins global security settings to use a fixed port for TCP connections and made sure it was one of my enabled ports, connection goes through cleanly now.

That said - this should NOT have worked on its own. When trying to connect earlier the logs clearly stated that connection attempts at the given port were refused (exact same port, and it was enabled then as well.)

I can understand if the agent was trying to connect at a different port, but I don't understand why dedicating the port itself would make a difference to the connecting agent.