Changing the configured CDN URL does not work

Issue Summary

After changing/updating the "CDN URL" property (Admin → System → Content Delivery Network) with a new URL, I noticed that some resources were still being requested by my browser which referenced the prior CDN URL, even with the browser's cache disabled or when using incognito windows. On further investigation, I found that these assets were being requested as downstream components by CSS and JS via URLs referencing the old CDN, even when loaded directly from Jira (bypassing new CDN). E.g.: when batch.css is loaded from new CDN or directly from Jira, it contains references to static asset adgs-icons.woff on old CDN.

Steps to Reproduce

1. Configure Jira with a CDN URL for the Content Delivery Network feature
2. Browse some pages (issues, dashboards, etc) on Jira to ensure static assets which reference the CDN are created and cached by Jira
3. Configure Jira with a new, different CDN URL

Expected Results

No requests should be made to load assets from the previously-configured CDN URL.

Actual Results

Browse some pages (issues, dashboards, etc) and view network traffic via the web inspector tool; see that some resources are still requested from previously-configured CDN.

This can also be seen by directly viewing the files located at $JIRA_HOME/tmp/webresources which will contain said references to files on the old CDN.

Workaround

1. Change CDN URL to new/desired value
2. Immediately delete the files located at $JIRA_HOME/tmp/webresources/*
3. If any pages were loaded between steps 1 and 2, you'll also need to invalidate those assets on the newly-configured CDN itself, as they will already have been retrieved and cached there as well.