In the end I built up an image based on Ubuntu 22.04 which does not mandate x86-64-v2. I installed the official Ceph packages and hacked here and there (e.g. it was necessary to set the uid and gid of the Ceph user and group identical to those used by the CentOS Stream 8 image to avoid to mess with filesystem permissions), now I'm upgrading the cluster and hopefully it will end up well. I hope that this way, if Red Hat will continue to provide Ceph packages for Ubuntu, I will be able to upgrade to Ceph 19 and beyond since also Ubuntu 24.04 does not need x86-64-v2. I'd have to figure out how to upgrade cephadm on the hosts (which run Rocky Linux 8) now that the official build is discontinued, but I'll cope with that later. Thanks to everybody for the help; if anyone is interested I can share the Dockerfile. Cheers, Nicola