We has a serious issue in our Jenkins environment. Some times (or better after a a while) we can not connect any jar agents via command line from agent to built.in node.

We use port 50000 for JNLP communication and the log on agent side throws something like this

My first thing was, that we runs behind proxys, firewall ... and something happens there.

BUT:

+ This is only for new connections. Old (currently connected) connections are still fine.

+ and it  when I execute curl directly in the image it looks to fail too.

 sudo docker exec -it etm_test_jenkins  curl https://localhost:5000/
curl: (7) Failed to connect to localhost port 5000: Connection refused

and the connection to Jenkins URL looks fine:
udo docker exec -it etm_test_jenkins  curl https://localhost:8443/
curl: (60) SSL certificate problem: self signed certificate in certificate chain
More details here: https://curl.se/docs/sslcerts.html

Can somebody look here. It is more or less a critical point for us. Sometimes we runs 1 month without this issue, But sometimes (like now) we get the same issue in few days (currently 4 days)

And one important thing. Restart of Jenkins helps always!!! But this is not applicable solution.