Using LXD with Juju

Choosing LXD as the backing cloud for Juju is an efficient way to experiment with Juju. It is also very quick to set up. With lightweight containers acting as Juju machines, even a moderately powerful laptop can create useful models, or serve as a platform to develop your own charms. Make sure you have enough local space for the containers though.

Constraints can be used with LXD containers (v.2.4.1). However, these are not bound to the LXD cloud type (i.e. they can affect containers that are themselves backed by a Juju machine running on any cloud type). See Constraints and LXD containers for details.

Software prerequisites

Both LXD and Juju will be needed on the host system.

Install Juju now (see the Installing Juju page).

Then follow the instructions below for installing LXD based on your chosen Ubuntu release. Note that the snap install method will soon become the preferred way to install LXD. See Using the LXD snap for how to do this.

Ubuntu 14.04 LTS

On Trusty, install LXD from the 'trusty-backports' pocket. This will ensure a recent (and supported) version is used:

sudo apt install -t trusty-backports lxd

Ubuntu 16.04 LTS

On Xenial, install LXD from the 'xenial-backports' pocket. This will ensure a recent (and supported) version is used:

sudo apt install -t xenial-backports lxd 

Ubuntu 16.10 and greater

On these releases, install LXD in the usual way:

sudo apt install lxd

User group

In order to use LXD, the system user who will act as the Juju operator must be a member of the 'lxd' user group. Ensure that this is the case (below we assume this user is 'john'):

sudo adduser john lxd

The user will be in the 'lxd' group when they next log in. If the intended Juju operator is the current user all that's needed is a group membership refresh:

newgrp lxd

You can confirm the active group membership for the current user by running the command:

groups

Alternate backing file-system

LXD can use various file-systems for its containers. Below we show how to implement ZFS, as it provides the best experience.

Proceed as follows:

sudo apt install zfsutils-linux
sudo mkdir /var/lib/zfs
sudo truncate -s 32G /var/lib/zfs/lxd.img
sudo zpool create lxd /var/lib/zfs/lxd.img
lxd init --auto --storage-backend zfs --storage-pool lxd

Above we allocated 32GB of space to a sparse file.

Notes:

• If possible, put /var/lib/zfs on a fast storage device (e.g. SSD).
• The installed ZFS utilities can be used to query the pool (e.g. sudo zpool list -v lxd).

If you've installed LXD via the snap package then you don't need to install the ZFS tools and configure it manually (as shown above). All that's required is:

lxd init --auto --storage-backend zfs

Disabling IPv6

Currently Juju does not support IPv6. You will therefore need to disable it at the LXD level. Assuming an LXD bridge of lxdbr0:

lxc network set lxdbr0 ipv6.address none

Creating a controller

The Juju controller for LXD (the 'localhost' cloud) can now be created. Below, we call it 'lxd':

juju bootstrap localhost lxd

View the new controller machine like this:

juju machines -m controller

This example yields the following output:

Machine  State    DNS            Inst id        Series  AZ  Message
0        started  10.103.91.114  juju-b14348-0  xenial      Running

The controller's underlying container can be listed with the LXD client:

lxc list

Output:

---------------+---------+----------------------+------+------------+-----------+
|     NAME      |  STATE  |         IPV4         | IPV6 |    TYPE    | SNAPSHOTS |
+---------------+---------+----------------------+------+------------+-----------+
| juju-b14348-0 | RUNNING | 10.103.91.114 (eth0) |      | PERSISTENT | 0         |
+---------------+---------+----------------------+------+------------+-----------+

LXD specific features

Here is a list of noteworthy LXD specific features and differences:

• LXD clustering is supported (v.2.4.0). See Additional LXD resources for details.

Additional LXD resources

Additional LXD resources provides more LXD-specific information.

Next steps

A controller is created with two models - the 'controller' model, which should be reserved for Juju's internal operations, and a model named 'default', which can be used for deploying user workloads.

See these pages for ideas on what to do next:

• Juju models
• Introduction to Juju Charms