Have jenkins setup on http port 8080 or AJP port 8009.

Put a reverse proxy in front of it (in this case apache)

Disable JNLP port.

Download and run the client tools:

java -jar jenkins-cli.jar -s http://192.168.122.3/ help

This will hang for some time and error out:

Exception in thread "main" java.io.IOException: Premature EOF
at sun.net.www.http.ChunkedInputStream.readAheadBlocking(ChunkedInputStream.java:556)
at sun.net.www.http.ChunkedInputStream.readAhead(ChunkedInputStream.java:600)
at sun.net.www.http.ChunkedInputStream.read(ChunkedInputStream.java:687)
at java.io.FilterInputStream.read(FilterInputStream.java:133)
at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:2582)
at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:2577)
at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:2566)
at hudson.remoting.Channel.<init>(Channel.java:406)
at hudson.remoting.Channel.<init>(Channel.java:366)
at hudson.remoting.Channel.<init>(Channel.java:327)
at hudson.remoting.Channel.<init>(Channel.java:323)
at hudson.remoting.Channel.<init>(Channel.java:311)
at hudson.cli.CLI.connectViaHttp(CLI.java:122)
at hudson.cli.CLI.<init>(CLI.java:105)
at hudson.cli.CLI.<init>(CLI.java:83)
at hudson.cli.CLI._main(CLI.java:267)
at hudson.cli.CLI.main(CLI.java:216)

I've attached a sample debug from jenkins in not working mode.

If I switch to using HAProxy, it succeeds but takes about 20 seconds to do so. Using the CLI to contact the port directly takes less than a second. Something here is causing non jnlp cli connections to fail.