[Azure Update Center] HTTP/404 on directories which are symlinks

[dduportal]

As reported by @MarkEWaite, we have at least one location which reports HTTP/404 on the new (Azure) Update Center while being served with no error on the (current) Update Center:

• https://azure.updates.jenkins.io/latest/ (and https://azure.updates.jenkins.io/latest) answers HTTP/404 Not Found (Apache Error):

• While https://aws.updates.jenkins.io/latest/ shows an HTML page with a list of relative links to all plugins:

[dduportal]

We identified the problem: it was an unexpected side effect of jenkins-infra/update-center2#816 (for the issue #4373) in which we switched from a "www/ -> rsync -> httpd-htdocs" pattern to a "www/ -> cp -> httpd-htdocs", before using azcopy to copy the "httpd-htdocs" to the Azure File Shares?
The unexpected change is that using cp copy the symlinks "as it" while rsync was derefencing them.
=> Sinc azcopy sync does NOT support symlinks, they are simply ignored since jenkins-infra/update-center2#816.

/latest/ is a symlink: it's now ignored by azcopy, e.g. it was removed, hence the HTTP/404

[dduportal]

Problem fixed by the following PR: jenkins-infra/update-center2#824 (note we did a first try, reverted it and then this PR). It now works: symlinks are dereferences first, and then copied "as file".