Following cluster instructions to configure an existing ezplatform installation for cluster don't fully work (I used ezplatform-demo as example), since existing images/media/files and other attachments are not in cluster var dir. Due that, we have several An error occurred while loading the image messages in backoffice.

I guess this is due the lack of the equivalent to clusterize.php from legacy cluster.
https://github.com/ezsystems/ezpublish-legacy/blob/d76ce9824dabaceeefa77530c8c611e447d1b109/bin/php/clusterize.php

Potential bugs found by Bård F. using 1.9 and Amazon S3:

• $metadataCreateStruct mtime expects a timestamp but gets a struct. Likely incompatibility due to clusterize script not being up to date with kernel code. Not a bug, already fixed by EZP-26760
• Paths on S3 do not contain "var/site/storage/" but clusterize expects it. Check S3 handler for how to deal with this, likely an easy fix. Not reproducible, probably already fixed by EZP-26760

I tested migrating to AWS S3. Worryingly, it worked on the first attempt. Doc: https://jira.ez.no/browse/EZP-27323