Monthly Archives: January 2017

Ubuntu Core in LXD containers

LXD logo

What’s Ubuntu Core?

Ubuntu Core is a version of Ubuntu that’s fully transactional and entirely based on snap packages.

Most of the system is read-only. All installed applications come from snap packages and all updates are done using transactions. Meaning that should anything go wrong at any point during a package or system update, the system will be able to revert to the previous state and report the failure.

The current release of Ubuntu Core is called series 16 and was released in November 2016.

Note that on Ubuntu Core systems, only snap packages using confinement can be installed (no “classic” snaps) and that a good number of snaps will not fully work in this environment or will require some manual intervention (creating user and groups, …). Ubuntu Core gets improved on a weekly basis as new releases of snapd and the “core” snap are put out.


As far as LXD is concerned, Ubuntu Core is just another Linux distribution. That being said, snapd does require unprivileged FUSE mounts and AppArmor namespacing and stacking, so you will need the following:

  • An up to date Ubuntu system using the official Ubuntu kernel
  • An up to date version of LXD

Creating an Ubuntu Core container

The Ubuntu Core images are currently published on the community image server.
You can launch a new container with:

stgraber@dakara:~$ lxc launch images:ubuntu-core/16 ubuntu-core
Creating ubuntu-core
Starting ubuntu-core

The container will take a few seconds to start, first executing a first stage loader that determines what read-only image to use and setup the writable layers. You don’t want to interrupt the container in that stage and “lxc exec” will likely just fail as pretty much nothing is available at that point.

Seconds later, “lxc list” will show the container IP address, indicating that it’s booted into Ubuntu Core:

stgraber@dakara:~$ lxc list
|     NAME    |  STATE  |          IPV4        |                      IPV6                    |    TYPE    | SNAPSHOTS |
| ubuntu-core | RUNNING | (eth0) | 2001:470:b368:b2b5:216:3eff:fee1:296f (eth0) | PERSISTENT | 0         |

You can then interact with that container the same way you would any other:

stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap list
Name       Version     Rev  Developer  Notes
core       16.04.1     394  canonical  -
pc         16.04-0.8   9    canonical  -
pc-kernel  4.4.0-45-4  37   canonical  -

Updating the container

If you’ve been tracking the development of Ubuntu Core, you’ll know that those versions above are pretty old. That’s because the disk images that are used as the source for the Ubuntu Core LXD images are only refreshed every few months. Ubuntu Core systems will automatically update once a day and then automatically reboot to boot onto the new version (and revert if this fails).

If you want to immediately force an update, you can do it with:

stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap refresh
pc-kernel (stable) 4.4.0-53-1 from 'canonical' upgraded
core (stable) 16.04.1 from 'canonical' upgraded
root@ubuntu-core:~# snap version
snap 2.17
snapd 2.17
series 16

And then reboot the system and check the snapd version again:

root@ubuntu-core:~# reboot

stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap version
snap 2.21
snapd 2.21
series 16

You can get an history of all snapd interactions with

stgraber@dakara:~$ lxc exec ubuntu-core snap changes
ID  Status  Spawn                 Ready                 Summary
1   Done    2017-01-31T05:14:38Z  2017-01-31T05:14:44Z  Initialize system state
2   Done    2017-01-31T05:14:40Z  2017-01-31T05:14:45Z  Initialize device
3   Done    2017-01-31T05:21:30Z  2017-01-31T05:22:45Z  Refresh all snaps in the system

Installing some snaps

Let’s start with the simplest snaps of all, the good old Hello World:

stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap install hello-world
hello-world 6.3 from 'canonical' installed
root@ubuntu-core:~# hello-world
Hello World!

And then move on to something a bit more useful:

stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap install nextcloud
nextcloud 11.0.1snap2 from 'nextcloud' installed

Then hit your container over HTTP and you’ll get to your newly deployed Nextcloud instance.

If you feel like testing the latest LXD straight from git, you can do so with:

stgraber@dakara:~$ lxc config set ubuntu-core security.nesting true
stgraber@dakara:~$ lxc exec ubuntu-core bash
root@ubuntu-core:~# snap install lxd --edge
lxd (edge) git-c6006fb from 'canonical' installed
root@ubuntu-core:~# lxd init
Name of the storage backend to use (dir or zfs) [default=dir]: 

We detected that you are running inside an unprivileged container.
This means that unless you manually configured your host otherwise,
you will not have enough uid and gid to allocate to your containers.

LXD can re-use your container's own allocation to avoid the problem.
Doing so makes your nested containers slightly less safe as they could
in theory attack their parent container and gain more privileges than
they otherwise would.

Would you like to have your containers share their parent's allocation (yes/no) [default=yes]? 
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 address should be used (CIDR subnet notation, “auto” or “none”) [default=auto]? 
What IPv6 address should be used (CIDR subnet notation, “auto” or “none”) [default=auto]? 
LXD has been successfully configured.

And because container inception never gets old, lets run Ubuntu Core 16 inside Ubuntu Core 16:

root@ubuntu-core:~# lxc launch images:ubuntu-core/16 nested-core
Creating nested-core
Starting nested-core 
root@ubuntu-core:~# lxc list
|    NAME     |  STATE  |         IPV4        |                       IPV6                    |    TYPE    | SNAPSHOTS |
| nested-core | RUNNING | (eth0) | fd42:2861:5aad:3842:216:3eff:feaf:e6bd (eth0) | PERSISTENT | 0         |


If you ever wanted to try Ubuntu Core, this is a great way to do it. It’s also a great tool for snap authors to make sure their snap is fully self-contained and will work in all environments.

Ubuntu Core is a great fit for environments where you want to ensure that your system is always up to date and is entirely reproducible. This does come with a number of constraints that may or may not work for you.

And lastly, a word of warning. Those images are considered as good enough for testing, but aren’t officially supported at this point. We are working towards getting fully supported Ubuntu Core LXD images on the official Ubuntu image server in the near future.

Extra information

The main LXD website is at:
Development happens on Github at:
Mailing-list support happens on:
IRC support happens in: #lxcontainers on
Try LXD online:

Posted in Canonical voices, LXD, Planet Ubuntu | Tagged | 5 Comments

LXD on Debian (using snapd)

LXD logo


So far all my blog posts about LXD have been assuming an Ubuntu host with LXD installed from packages, as a snap or from source.

But LXD is perfectly happy to run on any Linux distribution which has the LXC library available (version 2.0.0 or higher), a recent kernel (3.13 or higher) and some standard system utilities available (rsync, dnsmasq, netcat, various filesystem tools, …).

In fact, you can find packages in the following Linux distributions (let me know if I missed one):

We have also had several reports of LXD being used on Centos and Fedora, where users built it from source using the distribution’s liblxc (or in the case of Centos, from an external repository).

One distribution we’ve seen a lot of requests for is Debian. A native Debian package has been in the works for a while now and the list of missing dependencies has been shrinking quite a lot lately.

But there is an easy alternative that will get you a working LXD on Debian today!
Use the same LXD snap package as I mentioned in a previous post, but on Debian!


  • A Debian “testing” (stretch) system
  • The stock Debian kernel without apparmor support
  • If you want to use ZFS with LXD, then the “contrib” repository must be enabled and the “zfsutils-linux” package installed on the system

Installing snapd and LXD

Getting the latest stable LXD onto an up to date Debian testing system is just a matter of running:

apt install snapd
snap install lxd

If you never used snapd before, you’ll have to either logout and log back in to update your PATH, or just update your existing one with:

. /etc/profile.d/

And now it’s time to configure LXD with:

root@debian:~# lxd init
Name of the storage backend to use (dir or zfs) [default=dir]:
Create a new ZFS pool (yes/no) [default=yes]?
Name of the new ZFS pool [default=lxd]:
Would you like to use an existing block device (yes/no) [default=no]?
Size in GB of the new loop device (1GB minimum) [default=15]:
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.

And finally, you can start using LXD:

root@debian:~# lxc launch images:debian/stretch debian
Creating debian
Starting debian

root@debian:~# lxc launch ubuntu:16.04 ubuntu
Creating ubuntu
Starting ubuntu

root@debian:~# lxc launch images:centos/7 centos
Creating centos
Starting centos

root@debian:~# lxc launch images:archlinux archlinux
Creating archlinux
Starting archlinux

root@debian:~# lxc launch images:gentoo gentoo
Creating gentoo
Starting gentoo

And enjoy your fresh collection of Linux distributions:

root@debian:~# lxc list
|   NAME    |  STATE  |         IPV4          |                     IPV6                      |    TYPE    | SNAPSHOTS |
| archlinux | RUNNING | (eth0) | fd42:46d0:3c40:cca7:216:3eff:fe40:7b1b (eth0) | PERSISTENT | 0         |
| centos    | RUNNING | (eth0) | fd42:46d0:3c40:cca7:216:3eff:fe87:64ff (eth0) | PERSISTENT | 0         |
| debian    | RUNNING | (eth0) | fd42:46d0:3c40:cca7:216:3eff:feb4:e984 (eth0) | PERSISTENT | 0         |
| gentoo    | RUNNING | (eth0) | fd42:46d0:3c40:cca7:216:3eff:fe27:10ca (eth0) | PERSISTENT | 0         |
| ubuntu    | RUNNING | (eth0)  | fd42:46d0:3c40:cca7:216:3eff:fedc:f0a6 (eth0) | PERSISTENT | 0         |


The availability of snapd on other Linux distributions makes it a great way to get the latest LXD running on your distribution of choice.

There are still a number of problems with the LXD snap which may or may not be a blocker for your own use. The main ones at this point are:

  • All containers are shutdown and restarted on upgrades
  • No support for bash completion

If you want non-root users to have access to the LXD daemon. Simply make sure that a “lxd” group exists on your system and add whoever you want to manage LXD into that group, then restart the LXD daemon.

Extra information

The snapd website can be found at:

The main LXD website is at:
Development happens on Github at:
Mailing-list support happens on:
IRC support happens in: #lxcontainers on
Try LXD online:

Posted in Canonical voices, LXD, Planet Ubuntu | Tagged | 11 Comments

Running Kubernetes inside LXD

LXD logo


For those who haven’t heard of Kubernetes before, it’s defined by the upstream project as:

Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications.

It groups containers that make up an application into logical units for easy management and discovery. Kubernetes builds upon 15 years of experience of running production workloads at Google, combined with best-of-breed ideas and practices from the community.

It is important to note the “applications” part in there. Kubernetes deploys a set of single application containers and connects them together. Those containers will typically run a single process and so are very different from the full system containers that LXD itself provides.

This blog post will be very similar to one I published last year on running OpenStack inside a LXD container. Similarly to the OpenStack deployment, we’ll be using conjure-up to setup a number of LXD containers and eventually run the Docker containers that are used by Kubernetes.


This post assumes you’ve got a working LXD setup, providing containers with network access and that you have at least 10GB of space for the containers to use and at least 4GB of RAM.

Outside of configuring LXD itself, you will also need to bump some kernel limits with the following commands:

sudo sysctl fs.inotify.max_user_instances=1048576  
sudo sysctl fs.inotify.max_queued_events=1048576  
sudo sysctl fs.inotify.max_user_watches=1048576  
sudo sysctl vm.max_map_count=262144

Setting up the container

Similarly to OpenStack, the conjure-up deployed version of Kubernetes expects a lot more privileges and resource access than LXD would typically provide. As a result, we have to create a privileged container, with nesting enabled and with AppArmor disabled.

This means that not very much of LXD’s security features will still be in effect on this container. Depending on how you feel about this, you may choose to run this on a different machine.

Note that all of this however remains better than instructions that would have you install everything directly on your host machine. If only by making it very easy to remove it all in the end.

lxc init ubuntu:16.04 kubernetes -c security.privileged=true -c security.nesting=true -c linux.kernel_modules=ip_tables,ip6_tables,netlink_diag,nf_nat,overlay
printf "lxc.cap.drop=\nlxc.aa_profile=unconfined\n" | lxc config set kubernetes raw.lxc -
lxc config device add kubernetes mem unix-char path=/dev/mem
lxc start kubernetes

Then we need to add a couple of PPAs and install conjure-up, the deployment tool we’ll use to get Kubernetes going.

lxc exec kubernetes -- apt update
lxc exec kubernetes -- apt dist-upgrade -y
lxc exec kubernetes -- apt install squashfuse -y
lxc exec kubernetes -- ln -s /bin/true /usr/local/bin/udevadm
lxc exec kubernetes -- snap install conjure-up --classic

And the last setup step is to configure LXD networking inside the container.
Answer with the default for all questions, except for:

  • Use the “dir” storage backend (“zfs” doesn’t work in a nested container)
  • Do NOT configure IPv6 networking (conjure-up/juju don’t play well with it)
lxc exec kubernetes -- lxd init

And that’s it for the container configuration itself, now we can deploy Kubernetes!

Deploying Kubernetes with conjure-up

As mentioned earlier, we’ll be using conjure-up to deploy Kubernetes.
This is a nice, user friendly, tool that interfaces with Juju to deploy complex services.

Start it with:

lxc exec kubernetes -- sudo -u ubuntu -i conjure-up
  • Select “Kubernetes Core”
  • Then select “localhost” as the deployment target (uses LXD)
  • And hit “Deploy all remaining applications”

This will now deploy Kubernetes. The whole process can take well over an hour depending on what kind of machine you’re running this on. You’ll see all services getting a container allocated, then getting deployed and finally interconnected.

Once the deployment is done, a few post-install steps will appear. This will import some initial images, setup SSH authentication, configure networking and finally giving you the IP address of the dashboard.

Interact with your new Kubernetes

We can ask juju to deploy a new kubernetes workload, in this case 5 instances of “microbot”:

root@kubernetes:~# sudo -u ubuntu -i
ubuntu@kubernetes:~$ juju run-action kubernetes-worker/0 microbot replicas=5
Action queued with id: 1d1e2997-5238-4b86-873c-ad79660db43f

You can then grab the service address from the Juju action output:

ubuntu@kubernetes:~$ juju show-action-output 1d1e2997-5238-4b86-873c-ad79660db43f
status: completed
 completed: 2017-01-13 10:26:14 +0000 UTC
 enqueued: 2017-01-13 10:26:11 +0000 UTC
 started: 2017-01-13 10:26:12 +0000 UTC

Now actually using the Kubernetes tools, we can check the state of our new pods:

ubuntu@kubernetes:~$ kubectl.conjure-up-kubernetes-core-be8 get pods
default-http-backend-w9nr3 1/1 Running 0 21m
microbot-1855935831-cn4bs 0/1 ContainerCreating 0 18s
microbot-1855935831-dh70k 0/1 ContainerCreating 0 18s
microbot-1855935831-fqwjp 0/1 ContainerCreating 0 18s
microbot-1855935831-ksmmp 0/1 ContainerCreating 0 18s
microbot-1855935831-mfvst 1/1 Running 0 18s
nginx-ingress-controller-bj5gh 1/1 Running 0 21m

After a little while, you’ll see everything’s running:

ubuntu@kubernetes:~$ ./kubectl get pods
default-http-backend-w9nr3 1/1 Running 0 23m
microbot-1855935831-cn4bs 1/1 Running 0 2m
microbot-1855935831-dh70k 1/1 Running 0 2m
microbot-1855935831-fqwjp 1/1 Running 0 2m
microbot-1855935831-ksmmp 1/1 Running 0 2m
microbot-1855935831-mfvst 1/1 Running 0 2m
nginx-ingress-controller-bj5gh 1/1 Running 0 23m

At which point, you can hit the service URL with:

ubuntu@kubernetes:~$ curl -s | grep hostname
 <p class="centered">Container hostname: microbot-1855935831-fqwjp</p>

Running this multiple times will show you different container hostnames as you get load balanced between one of those 5 new instances.


Similar to OpenStack, conjure-up combined with LXD makes it very easy to deploy rather complex big software, very easily and in a very self-contained way.

This isn’t the kind of setup you’d want to run in a production environment, but it’s great for developers, demos and whoever wants to try those technologies without investing into hardware.

Extra information

The conjure-up website can be found at:
The Juju website can be found at:

The main LXD website is at:
Development happens on Github at:
Mailing-list support happens on:
IRC support happens in: #lxcontainers on
Try LXD online:

Posted in Canonical voices, LXD, Planet Ubuntu | Tagged | 5 Comments