[lxc-users] lxc 2.0 => 3.0 and ubuntu.common.conf (and lxc-templates dpkg)

[Adrian Pepper]

> From arpepper at uwaterloo.ca Mon Jul 16 15:40:10 2018
> From: AR Pepper <arpepper at uwaterloo.ca>
> To: "lxc-users at lists.linuxcontainers.org"
> 	<lxc-users at lists.linuxcontainers.org>
> CC: AR Pepper <arpepper at uwaterloo.ca>
> 
> This message devolved from a different query which is implied here together
> with its answer.  Perhaps this result will save some other people some time.
> 
> 
> I just discovered a stupid user (lxc administrator) trick.
> 
> Suppose you have an lxc setup you are migrating from Ubuntu 16.04 to 18.04.
> (Going from lxc 2.0(2.0.8) to 3.0(3.0.1)).
> (Doing a fresh install of Ubuntu 18.04 and modifying to match).
> 
> If under Ubuntu 18.04 you install the "lxc" package, but not the
> "lxc-templates" package, then, even after "lxc-update-config",
> some of your lxc config files will fail because of...
> (for example)
> 
> lxc.include = /usr/share/lxc/config/ubuntu.common.conf
> 
> 
> As an even stupider user trick, things seem to superficially work properly
> if you simply remove the "ubuntu." from the config file, leaving
> 
> lxc.include = /usr/share/lxc/config/common.conf
> 
> It turns out /usr/share/lxc/config/ubuntu.common.conf (and many others)
> are provided under Ubuntu by the "lxc-templates" package.
> 
> Hmm.  Could lxc-update-config (be changed to) remark upon the need for
> the lxc-templates package?  Or maybe just make a general observation
> that the include file does not exist?  ("Something is wrong")

While waiting for the above message to actually appear, I thought of a
perhaps better set of comments on the same thing.  As a follow-up to
Christian Brauner's packaging change announcement.

I eventually wonder (below) if "lxc" could once again have "lxc-templates"
as a dependency, even though "lxc-utils" does[should] not.  Since "lxc"
is now branded as a transitional package => lxc-utils.


Adrian Pepper
arpepper at uwaterloo.ca

> From lxc-users-bounces at lists.linuxcontainers.org Sat Apr  7 12:04:56 2018
> From: Christian Brauner <christian.brauner at canonical.com>
> Subject: [lxc-users] LXC 3.0.0: Packaging Changes To Be Aware Of
> 
> 
> Hey everyone,
> 
> LX{C,FS,D} upstream here. :)
> 
[...]
> 
> Here is a list of what we consider will most likely affect you as packagers:
> 
> 1. **Important** the lxc-templates have been moved out of the main LXC tree
>    into a separate repository
>    https://github.com/lxc/lxc-templates
> 
>    This means that without this separate package LXC will now only come with
>    the following templates:
> 
>    lxc-busybox
>    lxc-download
>    lxc-local
>    lxc-oci
> 

The templates had been in a separate "lxc-templates" package also in
Ubuntu 16.04.
But "lxc-templates" had been a dependency of the "lxc" package and
was therefore dragged in automatically.

But with the change indicated in the quoted announcement, it no longer
gets so dragged in.

But an unmentioned associated effect of not dragging in lxc-templates
is that most of the files
/usr/share/lxc/config/*.conf
are no longer put in place.

So "lxc-templates" must be installed not only to use the templates
to generate new containers.  It must be installed if you are going
bring forward containers from Ubuntu 16.04 (lxc 2.0), which had been
generated using templates.

"lxc-update-config" works without complaint on containers whose config
includes, for example

   lxc.include = /usr/share/lxc/config/ubuntu.common.conf

But the containers still fail afterwards because the include is not
satisfied.  (They fail, that is, until "lxc-templates" is installed).

(Assume here that a common way of producing an upgraded host system,
e.g. Ubuntu 18.04 versus 16.04, is to produce a new minimal 18.04
system and then apply all recorded "apt install" commands corresponding
to actual desired packages (yes, modifications are sometimes needed,
but...).  The old 16.04 system need not have explicitly done "apt
install lxc-templates" and so that could be overlooked in 18.04).

Since "lxc" is now branded as a transitional package => lxc-utils,
could "lxc" have lxc-templates as a dependency, even though lxc-utils
will not?


Adrian Pepper
arpepper at uwaterloo.ca