Issue #144 on go-proxmox was opened in April 2024 with the title “Weird sshkeys SSH public key validation error”. It is one of my less proud threads. It’s thirteen comments of people, including me, trying to get a public key into a cloud-init VM through the API. The working answer took more than a year to show up. The fix that finally landed in May is one line. Here’s why it took so long.

Proxmox’s built-in cloud-init support is fine for the basics: a user, an SSH key, an IP config. It falls apart the second you want your own user-data, vendor-data or a real network-config. The GUI and the ci* options only expose a handful of fields. The escape hatch is cicustom pointing at snippet files, and that means getting files onto the Proxmox host’s filesystem first. The usual alternative is building a nocloud ISO yourself with genisoimage or mkisofs. That means a system…

go-proxmox has had a CloudInit() helper since 2023. It builds a small nocloud ISO in Go, uploads it to Proxmox and mounts it on the VM as a CD-ROM. It’s always worked fine for Linux guests. It has never worked for Windows guests running cloudbase-init. The reason is a filesystem extension from 1995 called Joliet.