The use_ipv6 flag not only influences nova networking

[Denes Nemeth]

Description
===========

The use_ipv6 flag is marked as deprecated in the Ocata release (https://docs.openstack.org/ocata/config-reference/compute/config-options.html ) because it Nova networking is planed to be removed. However this flag also influences the data generated in the network_data.json. If the flag is set to false the IPv6 networks are missing from the JSON. If the value is true the JSON contains the IPv6 interfaces. Further details can be found here:
https://bugs.launchpad.net/nova/+bug/1514082

If default value (false) is also inconsistent with the data returned by Neutron through the meta data service. http://169.254.169.254/openstack/latest/network_data.json

Steps to reproduce
==================

1. Boot a server with 2 interfaces one IPv4 and one IPv6
2. mount /dev/sr0 /mnt
3. The /mnt/openstack/latest/network-data.json does not contain IPv6 addresses

0. Change the use_ipv6 flag to true on all compute nodes and restart the compute service
1. Boot a server with 2 interfaces one IPv4 and one IPv6
2. mount /dev/sr0 /mnt
3. The /mnt/openstack/latest/network-data.json does not contain IPv6 addresses

Expected result
===============

Option 0: Nova should donwload the network-data.json from the Neutron
metadata service and expose it as is on the config drive.

Option 1: Change the description of the use_ipv6 to: "Configures if the IPv6 addresses should be included in the config drive. (Remove deprecation warning)
Change the default value to true to be in sync with neutron behaviour.

Option 2: The generation of the network-data.json on config drive should always include the IPv6 addresses.

[Stephen Finucane (stephenfinucane)]

I'm pretty sure this is a a duplicate of another bug, but I've yet to find the other one. I'll chase this up over the course of the week.

[Stephen Finucane (stephenfinucane)]

Yeah, the related bug that I was thinking of is #1676363. It's not exactly the same thing though, so this should stay open.

[Stephen Finucane (stephenfinucane)]

I've looked into this and I'm not able to determine where this is being triggered. Commit c0aef97c49781f2ce0aa93fd33bfac7e68ea5b97 should have prevented this from happening, but it seems it did not. You're sure this is still an issue in Pike?

[Stephen Finucane (stephenfinucane)]

OK, so this really looks like it was fixed in [1]. We don't always expose IPv6 [2], but we seem to do so if the instance's 'network_info' object contains IPv6 subnets [3].

I'm not 100% on this, but I'm sure enough to mark this as invalid. Please reopen if I've missed something.

[1] https://review.openstack.org/#/c/430910/6/nova/virt/netutils.py
[2] https://github.com/openstack/nova/blob/16.0.0/nova/virt/netutils.py#L162-L164
[3] https://github.com/openstack/nova/blob/16.0.0/nova/virt/netutils.py#L131

[Dr. Jens Harbott (j-harbott)]

The issue is still present in Ocata, so the OP was correct. Would have been nice to backport the patch, but I assume that with Pike being released it is too late for that now.