@Tippon That is a big part of the point behind containers, you don't have any long term state inside them. Migration is just a case of copying the configuration over along with the contents of any persistent volumes.

It's worth looking into Podman instead of Docker, the daemon-less architecture makes it more lightweight and secure as it's easier to have rootless containers. Management can also be easer as being a Red Hat project it integrates well into Systemd.

With your existing server on Xubuntu you may as well stick with Ubuntu Server or Debian for the familiarity.

Extremely easy if you've set your projects up using docker compose files.

Just copy the compose file and data volumes over to the new host, run docker compose up -d and you're all set.

While I’m at it, is there a best OS to base everything on? Preferably free.

Debian, or Proxmox if you want a webUI for containers and VMs.

The data that your software interacts with is external to a container but can be mapped to the container file system so that the software can interact with it. For example, your Minecraft server relies on disk files consisting of the world state and server config files (and plugins if you have any). These will still be on your host system, not inside the container. In order to transfer this to another system, you have to take those files from your host and move them to the new host. Then copy your docker config files over too so you can start a new container that points to your files on disk and it should function the same as it did before, but possibly with a different IP address.

An easy way to think of it is that a container can be restarted, like maybe when you restart the PC. When a container is restarted, all the files in the container reset to their initial state. If you go into a container and create files then restart the container, those files will be gone. Any data that needs to be persisted between restarts needs to go on your host filesystem and volume mount it to the container.

Besides containers, you should look in Ansible too, you can automatize the creation of your infrastructure in other servers.

Docker is helpful, but won't be perfect since there's no built-in migration. You'll have to move any mounted directories like config and data and stuff. Docker is designed to be able spin up and down constantly, so it doesn't really hold any persistent data in the image itself.

Also, I know you want free, but have you considered unraid? If you really need free you can try truenas or freenas or whatever, but a user friendly linux distro isn't usually going to be too much overhead. I'd highly recommend unraid as a good option for users who need an easier way to work with all of their containers but don't want to go as far as setting up a kubernetes cluster or something.