Cloud-Init Support - Proxmox VE
https://pve.proxmox.com/wiki/Cloud-Init_SupportProxmox VE generates an ISO image to pass the Cloud-Init data to the VM. For that purpose, all Cloud-Init VMs need to have an assigned CD-ROM drive. Also many Cloud-Init images assume to have a serial console, so it is recommended to add a serial console and use it as display for those VMs. Preparing Cloud-Init Templates
Cloud-Init FAQ - Proxmox VE
https://pve.proxmox.com/wiki/Cloud-Init_FAQIn Proxmox VE cloud-init images are attached as ISO images via a virtual CDROM drive. In order to start using the cloud-init tab in the Web UI, you'll have to add such a drive. This can be done in the Hardware tab, by clicking the Add button and selecting CloudInit Drive. Afterwards, the options in the cloud-init tab become usable. Options User