Oops after upgrading to Jenkins 2.375.1: Could not load class: org.jenkins.ui.icon.IconSet

[amotl]

Dear lovely project maintainers,

first things first, I wish you a happy new year.

On upgrading our instance to Jenkins 2.375.1, we have been tripped by the issue outlined at JENKINS-69966.

Observation

Jenkins displays an Ooops page, and, while being started, does not work at all.

Problem

Could not load class: org.jenkins.ui.icon.IconSet.
Reason: java.lang.NoSuchMethodException: org.jenkins.ui.icon.IconSet.getSymbol()

org.apache.commons.jelly.JellyTagException: jar:file:/var/jenkins_cache/war/WEB-INF/lib/jenkins-core-2.375.jar!/hudson/model/View/sidepanel.jelly:75:50: <st:include> org.apache.commons.jelly.JellyTagException: jar:file:/var/jenkins_cache/war/WEB-INF/lib/jenkins-core-2.375.jar!/lib/layout/pane.jelly:81:29: <d:invokeBody> org.apache.commons.jelly.JellyTagException: jar:file:/var/jenkins_cache/war/WEB-INF/lib/jenkins-core-2.375.jar!/lib/layout/icon.jelly:70:93: <j:invokeStatic> Could not load class: org.jenkins.ui.icon.IconSet. Reason: java.lang.NoSuchMethodException: org.jenkins.ui.icon.IconSet.getSymbol(java.lang.String, java.lang.Integer, java.lang.String, java.lang.String, java.lang.String, java.lang.String)
	at org.apache.commons.jelly.impl.TagScript.handleException(TagScript.java:719)
	at org.apache.commons.jelly.impl.TagScript.run(TagScript.java:277)

Description

At JENKINS-69966, they say:

Occurs when cloud stats plugin is installed and at least one agent is tracked by cloud stats.
Most likely caused by jenkinsci/jenkins#7208.

Is there anything you could do about it?

With kind regards,
Andreas.

[MarkEWaite]

Have you installed the most recent release of the cloud stats plugin?

254.v47891b_b_5b_6f6 is the release that fixed that issue. There has also been release 267.v577e3742c282 that includes other changes.

In general, when updating to a new long term support release, it is important to also update to the most recent releases of plugins.

[amotl]

Dear Mark,

thank you for the quick and swift response. I admit we did not update the cloud stats plugin before upgrading to a new long term support release, and we will adjust our upgrade procedure accordingly in the future, as you suggested. Also, apologies for missing GH-30. I think we can consider this as being resolved. Sorry for the noise, and thank you so much.

With kind regards,
Andreas.