Mainly for security. I was originally looking at CoreOS but I liked the additional improvements by the UBlue team. Since I only want it to run containers, it is a huge security benefit to be immutable and designed specifically for that workflow.

The Ignition file is super easy to do, even for just one server (substitute docker for podman depending which you have):

Take a copy of the UCore butane file:

https://github.com/ublue-os/ucore/blob/main/examples/ucore-autorebase.butane

Update it with your SSH public key and a password hash by using this command:

# Get a password hash
podman run -ti --rm quay.io/coreos/mkpasswd --method=yescrypt

Then host the butane file in a temporary local webserver:

# Convert Butane file to Ignition file
podman run -i --rm quay.io/coreos/butane:release --pretty --strict < ucore-autorebase.butane > ignition.ign

# Serve the Igition file using a temp webserver
podman run -p 5080:80 -v "$PWD":/var/www/html php:7.2-apache

During UCore setup, type in the address of the hosted file, e.g. http://your_ip_addr:5080/ignition.ign

That's it - UCore configures everything else during setup.___