To the metadata servers? They presumably hold keys to access all kinds of backend systems anyway. The certs don't require any additional trust. There must already be infrastructure in place for deploying said keys.
You could also do a hybrid where each machine gets a volume with an x509 cert and key only root has access to which can then be used to mTLS to a network service (which can then manage the certs)
That'd be a hybrid of cloud init data volume and network service
you could, the problem with this approach is how do you manage these volumes and the infrastructure around it.
How do you get the keys on that volume?
Usually, this trust is established when the machine is built the first time and it gets an identity and a cert assigned to it. You have the same problems (of how you control the infra and ensure that you and only you can do this on the network).
