jetty:run run time surprises?

[Mark Waite]

During an investigation into a git plugin bug report that it does not load correctly when installed from Jenkins core started with jetty:run, I found some surprising issues that I can't explain or resolve.

1. The reverse proxy configuration warning persists even if the Jenkins URL is configured in "Manage Jenkins" / "System".  All my attempts to resolve it have failed.  If I run Jenkins with java -jar war/target/jenkins.war , then I don't have any issue with the reverse proxy configuration warning
2. Starting an ssh build agent fails with the message:
   Copying latest remoting.jar... java.io.IOException: Could not copy remoting.jar into '/home/mwaite/rhel-8-a.markwaite.net-mwaite' on agent

I run Jenkins from my development directory with the command JENINS_HOME=work java -jar war/target/jenkins.war so I don't see those issues in my regular development work.  How do others run Jenkins core from their development directory?

Details of the steps that I took while testing jelly:run are available in a GitHub comment.

Are others seeing those issues?  Am I making a fundamental mistake?

Mark Waite

[Tim Jacomb]

I believe the 1st one is a known issue, implementing something like we do in maven-hpi-plugin that runs plugin dev servers with a forked process using Winstone would resolve it.

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[Daniel Beck]

> On 15. Mar 2026, at 16:49, Tim Jacomb <timja...@gmail.com> wrote:
>
> I believe the 1st one is a known issue, implementing something like we do in maven-hpi-plugin that runs plugin dev servers with a forked process using Winstone would resolve it.

Specifically, the reverse proxy monitor encodes unusual characters in URLs (IIRC the url-encoded forward slash %2f, among others) to test that they're correctly encoded/decoded. They are being rejected by default in recent versions of Jetty, and jetty:run uses that default. Jetty in Winstone is set up to accept these.

[Jesse Glick]

On Sun, Mar 15, 2026 at 11:58 AM Tim Jacomb <timja...@gmail.com> wrote:

something like we do in maven-hpi-plugin that runs plugin dev servers with a forked process using Winstone

https://github.com/jenkinsci/maven-hpi-plugin/pull/862 for the record. Would make sense to replace `jetty:run` the same way. Maybe `hpi:run` can be tweaked to work on the `jenkins-war` project, basically just declining to prepopulate `work/plugins/`?

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