xenial containers on trusty host need lxc packages from trusty-backports

[Adam Collard]

Steps to reproduce with Juju 1.25.5, given an environments.yaml with default-series: trusty. Reproduced on MAAS 1.9.2.

$ juju bootstrap
# wait for it to finish, noting we have a Trusty machine
$ juju deploy cs:xenial/ubuntu --to lxc:0

Note that we're stuck allocating the container, "Waiting for agent initialization to finish".

Looking on the machine in the console log of the Xenial template container, we can see

"
Failed to mount cgroup at /sys/fs/cgroup/systemd: Permission denied
[!!!!!!] Failed to mount API filesystems, freezing.
Freezing execution.
"

This is because lxc needs to be installed from trusty-backports. By tearing down the failed attempts, killing the stuck template container then

"sudo apt install -t trusty-backports lxc lxc-templates"

and trying the deploy again, it worked successfully.

See bug 1590547 for why you need to explicitly install lxc-templates

Upstream issue: https://github.com/lxc/lxc/issues/685

[David Britton (dpb)]

Also this one: https://bugs.launchpad.net/juju/+bug/1656027

[John A Meinel (jameinel)]

Can you give background where we need to support Xenial containers with 1.25? My concern is that if we switch to backports to support Xenial containers it is a fairly strong disturbance for things that are currently running Production environments using the LXC version that is officially part of Trusty.

If we have a customer that is saying "no, I have to use Trusty as the Host machines, using Juju 1.25 and I need Xenial machines", then we can evaluate this. But it does feel like a potential regression for a bunch of other people if the LXC in backports is at all different from the version that is in Trusty itself. (it would fix this problem, but we'd open ourselves up to breaking other people).

I'd like to mark this as Won't Fix for 1.25 because of the potential for regression in order to fix this, but if we do have someone who really needs it we can do it.

It isn't *hard* to have a case for "if installing LXC on Trusty use backports". The hard part is making sure we don't break everyone when they roll from 1.25.X to 1.25.Y and suddenly their new machines aren't running the same version of LXC that they've vetted everything against.

[Matt Rae (mattrae)]

I'm working with a customer who has asked if we will support Xenial containers on Trusty hosts with 1.25 without needing the workaround. The manual workaround is a solution for them but I believe xenial-backports packages aren't officially supported.

[Launchpad Janitor (janitor)]

[Expired for juju-core 1.25 because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for juju-core because there has been no activity for 60 days.]