What are snaps?

Snaps were introduced a little while back as a cross-distro package format allowing upstreams to easily generate and distribute packages of their application in a very consistent way, with support for transactional upgrade and rollback as well as confinement through AppArmor and Seccomp profiles.

It’s a packaging format that’s designed to be upstream friendly. Snaps effectively shift the packaging and maintenance burden from the Linux distribution to the upstream, making the upstream responsible for updating their packages and taking action when a security issue affects any of the code in their package.

The upside being that upstream is now in complete control of what’s in the package and can distribute a build of the software that matches their test environment and do so within minutes of the upstream release.

Why distribute LXD as a snap?

We’ve always cared about making LXD available to everyone. It’s available for a number of Linux distribution already with a few more actively working on packaging it.

For Ubuntu, we have it in the archive itself, push frequent stable updates, maintain official backports in the archive and also maintain a number of PPAs to make our releases available to all Ubuntu users.

Doing all that is a lot of work and it makes tracking down bugs that much harder as we have to care about a whole lot of different setups and combination of package versions.

Over the next few months, we hope to move away from PPAs and some of our backports in favor of using our snap package. This will allow a much shorter turnaround time for new releases and give us more control on the runtime environment of LXD, making our lives easier when dealing with bugs.

How to get the LXD snap?

Those instructions have only been tested on fully up to date Ubuntu 16.04 LTS or Ubuntu 16.10 with snapd installed. Please use a system that doesn’t already have LXD containers as the LXD snap will not be able to take over existing containers.

1. Make sure you don’t have a packaged version of LXD installed on your system.

   sudo apt remove --purge lxd lxd-client

2. Create the “lxd” group and add yourself to it.

   sudo groupadd --system lxd
   sudo usermod -G lxd -a <username>

3. Install LXD itself

   sudo snap install lxd

This will get the current version of LXD from the “stable” channel.
If your user wasn’t already part of the “lxd” group, you may now need to run:

newgrp lxd

Once installed, you can set it up and spawn your first container with:

1. Configure the LXD daemon

   sudo lxd init

2. Launch your first container

   lxd.lxc launch ubuntu:16.04 xenial

Channels and updates

The Ubuntu Snap store offers 4 different release “channels” for snaps:

• stable
• candidate
• stable
• edge

For LXD, we currently use “stable”, “candidate” and “edge”.

• “stable” contains the latest stable release of LXD.
• “candidate” is a testing area for “stable”.
  We’ll push new releases there a couple of days before releasing to “stable”.
• “edge” is the current state of our development tree.
  This channel is entirely automated with uploads triggered after the upstream CI confirms that the development tree looks good.

You can switch between channels by using the “snap refresh” command:

snap refresh lxd --edge

This will cause your system to install the current version of LXD from the “edge” channel.

Be careful when hopping channels though as LXD may break when moving back to an earlier version (going from edge to stable), especially when database schema changes occurred in between.

Snaps automatically update, either on schedule (typically once a day) or through push notifications from the store. On top of that, you can force an update by running “snap refresh lxd”.

Known limitations

• We don’t currently support live-migration (CRIU) with the LXD snap.
• The “lxd” group must exist prior to installation.
• Updating the snap restarts all LXD containers.
• The “lxd” snap can’t provide the “lxc” command (use “lxd.lxc”).
• LXD always runs even when it’s unused.

Those are all pretty major usability issues and will likely be showstoppers for a lot of people.
We’re actively working with the Snappy team to get those issues addressed as soon as possible and will keep maintaining all our existing packages until such time as those are resolved.

Extra information

More information on snap packages can be found at: http://snapcraft.io
Bug reports for the LXD snap: https://github.com/lxc/lxd-pkg-ubuntu/issues

The main LXD website is at: https://linuxcontainers.org/lxd
Development happens on Github at: https://github.com/lxc/lxd
Mailing-list support happens on: https://lists.linuxcontainers.org
IRC support happens in: #lxcontainers on irc.freenode.net
Try LXD online: https://linuxcontainers.org/lxd/try-it

PS: I have not forgotten about the remaining two posts in the LXD 2.0 series, the next post has been on hold for a while due to some issues with OpenStack/devstack.