Creating a Proxmox virtual machine in seconds instead of minutes

The usual way to create a virtual machine on Proxmox is to download an ISO, attach it to the machine and click through the installer from start to finish. It works, but it spends the same twenty minutes on every machine. For server work there is a much shorter road.

What a cloud image is

A cloud image is a system the distribution team has already installed and written to a disk. It is not installation media; it is a finished disk file. It usually weighs a few hundred megabytes, and the machine shows no installer on first boot, it simply comes up. Ubuntu, Debian, AlmaLinux and Rocky publish these images officially.

What cloud-init does on first boot

A ready disk is not enough on its own, because it holds no user and no network name. Cloud-init fills exactly that gap: on the first boot it creates the user, places the SSH key, sets the network name and installs the packages you asked for. By the time the machine is up there is nothing left to do before connecting to it.

Turning it into a template

You do not need to download the image again for every machine. The image is turned into a template once, and later machines are cloned from it. Cloning is faster than copying a disk, and every machine still comes up with its own user and name, because cloud-init runs again on each clone.

When an ISO is still the right choice

Cloud images do not exist for every distribution, and they will not give you what you expect when a desktop environment is wanted. On the Windows side the road is different altogether. In those cases the ISO is correct; the cloud image is a shortcut for server work, not the only way.