Add UserContent mechanism

[timmjd]

What this PR does / why we need it

Implements a way to provide User Content files that will be served by Jenkins. Common use-case is to let Jenkins host a svg or png together with a custom css to customize the UI.

Which issue this PR fixes

Special notes for your reviewer

Checklist

• DCO signed
• Chart Version bumped
• CHANGELOG.md was updated

[torstenwalter]

I am not sure if this is the best way to achieve it. Wouldn't it be simpler to mount a config map or any other volume to that location?

I guess that's already possible, but it would not hurt to document in this PR how that works. From my perspective it's not strictly necessary that that volume is managed by this chart.

[timmjd]

The use-case I'd like to solve is to let Jenkins host a simple svg or png together with a custom css to adapt the styling of the UI - and that seems to be a quiet common use-case:

• https://medium.com/@elhayefrat/replace-jenkins-logo-and-text-to-your-choice-in-jenkinsui-f7d35daed25b
• https://nadavsvirsky.medium.com/customize-jenkins-favicon-dashboard-logo-f5c0b70d817d
• https://stackoverflow.com/a/70360371

To achieve this with the current implementation:

• Use the persistence.volumes & persistence.mounts option
  • Would require an external ConfigMap / Secret / PVC to be created outside the Helm context
• Create a custom Docker image where the content gets baked in
  • Would require to build & host the docker image: Additional CI & Hosting infrastructure
• Download the resources from an external source
  • Requires to host the content via a webserver infrastructure
• Write a plugin to host the content
  • Total overkill

All of these come with more or less overhead. Therefore, letting Jenkins host the files itself would be the most elegant one. Not sure if there is a more easy way to achieve this - any hint would be great.

[timmjd]

Hey @torstenwalter, I refactored to work with ConfigMaps instead of Secrets. Also it's possible to provide UTF-8 or binary encoded content separately. What's your suggestion?

[torstenwalter]

content looks ok. Would you mind adding a test for this?

https://github.com/jenkinsci/helm-charts/tree/main/charts/jenkins/unittests has quite some examples

[torstenwalter]

Is there a reason why you are mounting files individually instead of mounting all at once?

      - name: jenkins-user-contents
        mountPath: {{ $.Values.controller.jenkinsHome }}/userContent/
        readOnly: true

[timmjd]

If you mount the Configmap, K8S will create symlinks foobar.txt -> ..data/foobar.txt where ..data -> ..2020_03_03_16_40_36.675612011

Jenkins seems to be not supporting symlinks at this point - neither by displaying nor serving it:

Might be related to Jenkins Security Advisory 2021-01-13?

So you can not access userContent/foobar.txt directly but would need to go via something like userContent/..2020_03_03_16_40_36.675612011/foobar.txt - and this is an always changing URL.

[torstenwalter]

Thx for the clarification.

[torstenwalter]

@timmjd Sorry I lost track of this. You can ping me once the merge conflicts are resolved and a test is added otherwise this looks good to me.