Missing support for agent.jar location

[zhan9san]

What feature do you want to see added?

All except agent.jar location are supported to defined in environment variables.

docker-agent/jenkins-agent

Line 132 in 45445ae

exec $JAVA_BIN $JAVA_OPTIONS -jar /usr/share/jenkins/agent.jar $SECRET $AGENT_NAME $TUNNEL $URL $WORKDIR $WEB_SOCKET $DIRECT $PROTOCOLS $INSTANCE_IDENTITY $REMOTING_OPTS "$@"

Upstream changes

No response

Are you interested in contributing this feature?

yes

[dduportal]

Hi @zhan9san , thanks for raising this issue. Would you be willing to make a contribution by opening a PR implementing this feature request?

[dduportal]

Hi @zhan9san , thanks for your PR.
In this PR, you mentions the following element:

The jar file may be downloaded by the user who does not have write permission to directory, /usr/share/jenkins.

Could you describe the use case to see if further improvement could been made later (or in the documentation)?
It feels like you have a situation where you're not using the default container user, I would like to know more

[zhan9san]

Thanks for your attention.

It's a long story.

Currently, we are using customized jnlp image which is based on Ubuntu, Debian or CentOS. Using label is not recommended by Kubernetes plugin. It is a historical issue that we are still using it.

jenkins-agent in this repo is used as Entrypoint in our own image.

Previously, the business-related packages and jenkins-related packages are combined in one jnlp image. Each time we upgrade Jenkins, we need to rebuild the jnlp image as well because JDK/inbound version may be not supported in original image.

There are many jnlp images for different business groups. So, I want to decouple them.

---

How-to

Besides jnlp container, init container is introduced in pod to manage the jenkins-related logic.

Some existing image may define non-root USER in Dockerfile, which doesn't have write permission to /usr/share/jenkins.

JDK, agent.jar and jenkins-agent are downloaded in a shared volume, like /shared in init container. Note, the agent.jar is not in the default location /usr/share/jenkins/.

The Entrypoint of jnlp would be set to /shared/jenkins-agent, and JENKINS_JAVA_BIN would be set in jnlp container in pod template.

With this feature, I'll set JENKINS_AGENT_FILE as well.

It is inspired by https://issues.jenkins.io/browse/JENKINS-64778

Hope I express myself clear.

[dduportal]

Thanks for the clear explanation @zhan9san . I was interested by this details to see if there wasn't an additional way (documentation improvement, adding a new feature to the images, anything else) for us (maintainers) to help.

It looks like, as per your analysis, there is nothing else except delivering your contribution.
Many thanks for taking this time, I'm 100% sure it will help other users!

[zhan9san]

To be exact, it is in https://github.com/zhan9san/init-jnlp/blob/main/README.md?plain=1#L58-L59

[dduportal]

Your new feature is now available: https://hub.docker.com/r/jenkins/inbound-agent/tags?page=&page_size=&ordering=&name=3261.v9c670a_4748a_9-2%20