Proxmox
Convert the Ubuntu cloud image just uploaded to a disk of the VM just created.
SSH to Proxmox and login root account.
cd /var/lib/vz/template/iso
qm importdisk <VM_ID> <image_file> <storage_name>
qm set <VM_ID> --virtio0 <storage_name>:vm-<VM_ID>-disk-0
qm set <VM_ID> --boot c --bootdisk virtio0
qm set <VM_ID> --ide0 <storage_name>:cloudinit
resize the disk after config