I tried cloud-init with ubuntu-18.04-minimal-cloudimg-amd64.img from official link, ubuntu-18.04-server-cloudimg-amd64.img from this link and bionic-server-cloudimg-amd64.img from this link. They were all failed to boot with "No bootable disk" messages alike. I had followed Cloud-Init_Support section of proxmox wiki and reviewed Cloud-Init_FAQ also. My proxmox VE version is 6.0-15. What can I do to find the key to solve this situation?