It's really annoying that the default Ubuntu ISO (and I guess others, though I haven't tested) do not read cloud-config stuff in userdata. It would be great for this to be enabled. It looks like maybe it used to work pre-2017 according to the Vultr docs but then you guys just gave up and stopped maintaining it or something?
In any case for affected users, I am currently using a workaround of installing, configuring, and enabling cloud-init, dropping in a hacked DataSourceVultr.py to let cloud-init read the vultr metadata service, and saving the above as a snapshot which I can then instantiate as-needed.
I've made the above available in my repo https://github.com/akdor1154/vultr-ubuntu-cloudinit , but I'd really love it if the Vultr guys could take and build on that to make this work out-of-the-box. Snapshotting and restoring is quite slow (I guess I've been spoiled by the magic of EBS).