Andrew Mann wrote: >What's the use case for an IPv6 endpoint? This service is just for instance >metadata, >so as long as a requirement to support IPv4 is in place, using solely an IPv4 >endpoint >avoids a number of complexities:
The obvious use case would be deprecation of IPv4, but the question is when. Should I expect to be able to run a VM without IPv4 in 2014 or is IPv4 mandatory for all VMs? What about the year 2020 or 2050 or 2100? Do we ever reach a point where we can turn off IPv4 or will we need IPv4 for eternity? Right now it seems that we need IPv4 because cloud-init itself doesn’t appear to support IPv6 as a datasource. I’m going by this documentation http://cloudinit.readthedocs.org/en/latest/topics/datasources.html#what-is-a-datasource where the “magic ip” of 169.254.169.254 is referenced as well as some non-IP mechanisms. It wouldn’t be sufficient for OpenStack to support an IPv6 metadata address as long as most tenants are likely to be using a version of cloud-init that doesn’t know about IPv6 so step one would be to find out whether the maintainer of cloud-init is open to the idea of IPv4-less clouds. If so, then picking a link local IPv6 address seems like the obvious thing to do and the update to Neutron should be pretty trivial. There are a few references to that “magic ip” https://github.com/openstack/neutron/search?p=2&q=169.254.169.254&ref=cmdform but the main one is the iptables redirect rule in the L3 agent: https://github.com/openstack/neutron/blob/master/neutron/agent/l3_agent.py#L684
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