Last time I helped administer a deployment on one of these clouds, one of the first things we did on the startup script for the instances was to install an ipta

Last time I helped administer a deployment on one of these clouds, one of the first things we did on the startup script for the instances was to install an iptables rule so that only uid 0 (root) could talk to the metadata servers. The need for that kind of firewall rule on every instance shows that these metadata servers are a bad design. It would be much better if, instead of the network, these metadata servers were only visible as a PCIe or MMIO device. Of course, that would require a driver to be written, so at least initially, unmodified distributions would not be able to be used (but after a few years, every Linux and BSD distribution, and perhaps even Windows, would have that driver by default). That way, it would (on Linux) appear as files on /sys, readable only by root, without requiring any local firewall.