Encountering a 502 Bad Gateway error when fetching the slave-agent.jnlp file through the swarm client. I have traced this down to being an issue with the way the no_proxy settings are evaluated in Jenkins remoting (swarm is currently evaluating the proxy settings correctly but remoting is not). It currently will ignore any no_proxy settings that consist of hostnames without a domain suffix, i.e. "localhost" or "jenkinsmaster".
The use case for this is that I am running a docker swarm on a corporate proxy and need to be able to exclude my Jenkins master from the proxy in order for the slaves to be able to communicate.
I believe this is a simple fix here: https://github.com/jenkinsci/remoting/blob/master/src/main/java/hudson/remoting/Util.java#L132-L140
The regex should be changed such that the '.' is optional and that the hostname/domain can have underscores '_'.