Looks like I'm gonna exclude most of our #FCOS VMs from daily Proxmox #Backup Server.
Those FCOS VMs tasks are running containers. All we need is just backup quadlet files and /etc/default. For most of container's data, I think we can use application level replication. If it's not available, I rather backup those container's volumes.
Why?
Because full backup of vm disk images is too expensive. Not talking about storage price, but about extraneous load on infrastructures (cpu, storage i/o).
Fedora CoreOS Stable v43.20260316.3.1 has been released few hours ago with 49 packages upgraded, including kernel upgrade from 6.18.13 to 6.19.7.
UniFi OS Server installs just fine on Fedora CoreOS when doing "rpm-ostree usroverlay" before starting the installer.
This will allow it to create symlinks in /usr/bin which are not needed and don't need to be persisted. Without temporarily enabling usroverlay the installer will leave UniFi OS Server in a broken state.
Coreos is a great match for UniFi OS because the base system will upgrade automatically while application upgrades are managed by UniFi.
Aaaand it won't. Of course it wants to write in places where it's not even sane to write to on a mutable OS.
New stable Fedora CoreOS release available: 43.20260105.3.0
https://www.fedoraproject.org/coreos/release-notes?arch=x86_64&stream=stable
Major learning curve to use #fedora #coreos is how to create ignition file. #FCOS installation use that for installation configuration. There's no menu or wizard like other #linux distros.
Why? Because one of major goal of #FCOS is to enable easy mass deployment of similar configuration.
After you learn and solved that problem, remaining else is just systemd and #podman #quadlet (most #fcos deployment is to run containerized applications)
@zrail I've managed some #fedora #coreos to run dozens of #podman container. Works nicely.
I can depend zincati to auto-update os, and podman-auto-update systemd service to update container isafely. #fcos update is atomic update.
No need to doing manual major distro upgrade because zincati take care of that.
Yes, u should monitor memory usage. You can run #promotheus & grafana container to monitor it. Also there is prometheus-podman-exporter to monitor podman container with prometheus easily.
I figured out how to make a Fedora CoreOS template for XCP-ng that supports unattended installs by supplying an ignition file through Xen Orchestra's cloud config templates!
Adhidarma Hadiwinoto 
Markus Lindenberg
Echo Nar