In the spec we said:
"""
When the metadata proxy processes a request, it gathers the L2 addresses
of a VM, and the source interface, and passes it to the metadata service.
The Metadata service, instead of using the VM IP, uses the "VM MAC" and
"Gateway MAC" to identify the instance.
"""
But since we switched from the home-grown metadata-ns-proxy to haproxy
we no longer control some of the headers included, like X-Forwarded-For.
haproxy allows us to turn X-Forwarded-For on or off, but it cannot
give us an X-Forwarded-For-MAC header.
Instead it seems we have to rely on the source address being the IPv6
link local address generated from the NIC's MAC address as specified
in RFC 4291:
https://tools.ietf.org/html/rfc4291#section-2.5.6https://tools.ietf.org/html/rfc4291#appendix-A
Note that means you cannot use IPv6 Privacy Extensions:
https://tools.ietf.org/html/rfc4941
Change-Id: Ife592fcfc69e26f61ec1f45c06821cb025cc7cf2
Closes-Bug: #1460177
a818c41c25