rc3, lxd 2.4.1, 16.04/16.10 use ipv6 if configured via lxd init

[Adam Stokes]

To reproduce:

$ sudo lxd init

Name of the storage backend to use (dir or zfs) [default=dir]: dir
Would you like LXD to be available over the network (yes/no) [default=no]?
Would you like stale cached images to be updated automatically (yes/no) [default=yes]?
Would you like to create a new network bridge (yes/no) [default=yes]?
What should the new bridge be called [default=lxdbr0]?
What IPv4 subnet should be used (CIDR notation, “auto” or “none”) [default=auto]?
What IPv6 subnet should be used (CIDR notation, “auto” or “none”) [default=auto]?
LXD has been successfully configured.

Accept all defaults including auto for both ipv4 and ipv6

$ sudo apt install conjure-up
$ conjure-up -d

Select OpenStack with NovaLXD, wait awhile, check `juju status`: http://paste.ubuntu.com/23309595/
and yaml output: http://paste.ubuntu.com/23309596/

Output of `lxc network show lxdbr0`
name: lxdbr0
config:
  ipv4.address: 10.91.83.1/24
  ipv4.nat: "true"
  ipv6.address: fd42:c688:e4ad:4b78::1/64
  ipv6.nat: "true"
managed: true
type: bridge
usedby:
- /1.0/containers/juju-2ad2fc-0
- /1.0/containers/juju-2ad2fc-1
- /1.0/containers/juju-2ad2fc-10
- /1.0/containers/juju-2ad2fc-11
- /1.0/containers/juju-2ad2fc-12
- /1.0/containers/juju-2ad2fc-13
- /1.0/containers/juju-2ad2fc-14
- /1.0/containers/juju-2ad2fc-15
- /1.0/containers/juju-2ad2fc-2
- /1.0/containers/juju-2ad2fc-3
- /1.0/containers/juju-2ad2fc-4
- /1.0/containers/juju-2ad2fc-5
- /1.0/containers/juju-2ad2fc-6
- /1.0/containers/juju-2ad2fc-7
- /1.0/containers/juju-2ad2fc-8
- /1.0/containers/juju-2ad2fc-9
- /1.0/containers/juju-65a05a-0

I was told Juju 2.0 doesn't fully support ipv6 and should use ipv4 regardless of the configuration for LXD networking.

[Jason Hobbs (jason-hobbs)]

Seeing the same thing with 16.04 and 2.0rc3. Sometimes it uses IPv4, sometimes it uses IPv6.

[Andrew McDermott (frobware)]

I'm making a guess that the reason we haven't run into this since landing:

  https://github.com/juju/juju/pull/6338

which fixed:

  https://launchpad.net/bugs/1624495

is because we have only been testing with LXD 2.0.x.

[Andrew McDermott (frobware)]

We have https://github.com/juju/juju/pull/6430 proposed as a fix but I'm also going to look at fixing this in the core address selection logic in Juju. PR #6430 addresses LXD specifically but we really want a core fix.