Align Fedora packaging Java version and CI artifact handling with Jenkins support policy

[beri04]

Problem

While working on Fedora packaging and CI validation, I noticed two related issues:

1. The Fedora 42+ packaging installs Temurin Java 21, but Jenkins currently supports Java 17 as the required LTS runtime. This can lead to packaging installing an unsupported Java version for Jenkins.
2. The current CI pipeline uses a hard-coded filesystem path (/var/tmp) for handling build artifacts, which is outside the Jenkins workspace and does not follow standard Jenkins CI conventions.

Expected behavior

• Fedora packaging should install a Java version that aligns with Jenkins' supported runtimes (Java 17).
• CI build artifacts should remain within the Jenkins workspace (e.g. target/) and avoid hard-coded global filesystem paths.

Proposed direction

• Update Fedora packaging logic to install Temurin 17 until Jenkins officially supports Java 21.
• Adjust the Jenkinsfile to keep build artifacts within the workspace.

I wanted to open this issue first to confirm the approach with maintainers before continuing work on the PR.

[beri04]

any updates @dduportal

[lemeurherve]

Same remark as in #331 (comment):

let's wait for jenkins-infra/helpdesk#4945 completion first.

Our hands are full at the moment, we'll look at that issue when time permits, no need to ping us.

[dduportal]

1. The Fedora 42+ packaging installs Temurin Java 21, but Jenkins currently supports Java 17 as the required LTS runtime. This can lead to packaging installing an unsupported Java version for Jenkins.

That is incorrect: Jenkins weekly line requires JDK 21 since 1-2 weeks and LTS supports both JDK17 and JDK21 since months. As such, proposing JDK21 as the default looks like a better way to move forward.

Fedora packaging should install a Java version that aligns with Jenkins' supported runtimes (Java 17).

I have to disagree with this hypothesis. How would you manage the case of user who want to install Jenkins on Fedora 42+ with their own JDK distribution?

[beri04]

Thanks for the clarification, i missed the recent changes in Jenkins java support, given that LTS supports both JDK 17 and JDK 21, and weekly requires JDK 21, I agree that defaulting to JDK 21 on Fedora 42+ makes sense.
And about the users who wants to manage their own jdk distributions my thinking would be to avoid enforcing a strict dependency and instead like allowing the jenkins to run with the externally provided jdk (if possible) or document it to override the default java section.
I am happy to adjust or drop this proposal if current fedora already handlesthis use cases correctly.

[dduportal]

I am happy to adjust or drop this proposal if current fedora already handles this use cases correctly.

If you want to contribute, I believe you should try to reproduce the problem you want to fix first on your own. It would serve as a self-prove that your change does the expected change before even opening a PR.

If you are not able to reproduce (and share a reproducible example) then maybe it means there are no problem to solve (as frustrating as it can be :).