Metadata over IPv6

[Brian Haley <[e-mail]>]

Hi ipv6-list,

I was an IPv6 contributor many moons ago, and remembered this list when 
looking into something on a new project, was hoping to get some IPv6 
advice (below).

The current project I'm working on, Openstack Neutron, is an SDN 
networking project focused on delivering networking-as-a-service (NaaS) 
in virtual compute environments.

One thing that happens when a virtual machine boots is it typically asks 
for metadata, thing like ssh keys, and other configuration information 
required to make it functional.  It does this via requests to the URL 
http://169.254.169.254/latest/meta-data/... ([0] has more complete 
info).  This link-local IPv4 address was defined by AWS and is widely 
used across all types of clouds.

This works fine for dual-stack hosts, but more and more we're seeing 
IPv6-only networking scenarios that we don't support metadata with, so 
our community is looking to define an IPv6 address to use for this 
service.  My question to the list is - do you see a problem with us just 
defining an IPv6 link-local address for this same service?  Or do you 
think we need to propose a spec for it, in order to get IANA to reserve 
it?  We're trying to use a similar address, fe80::a9fe:a9fe 
(169.254.169.254 in hex - see [1] for more details), so it essentially 
looks the same.  We did think about using DNS to discover it, but for 
now just using a hard-coded link-local seems like a quicker way forward.

Thanks for any comments or advice!

-Brian Haley

[0] 
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instancedata-data-retrieval.html
[1] https://review.opendev.org/#/c/315604/