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.. _tutorial_lxd:
Quick-start tutorial with LXD
*****************************
In this tutorial, we will create our first cloud-init user-data script and
deploy it into a `LXD`_ container.
Why LXD?
========
We'll be using LXD for this tutorial because it provides first class support
for cloud-init user-data, as well as ``systemd`` support. Because it is
container based, it allows us to quickly test and iterate upon our user-data
definition.
Install and initialize LXD
==========================
If you already have LXD set up, you can skip this section. Otherwise, let's
install LXD:
.. code-block:: shell-session
$ sudo snap install lxd
If you don't have snap, you can install LXD using one of the
`other installation options`_.
Now we need to initialize LXD. The minimal configuration will be enough for
the purposes of this tutorial. If you need to, you can always change the
configuration at a later time.
.. code-block:: shell-session
$ lxd init --minimal
Define our user-data
====================
Now that LXD is set up, we can define our user-data. Create a file on your
local filesystem at :file:`/tmp/my-user-data` and populate it with this
content:
.. code-block:: yaml
#cloud-config
runcmd:
- echo 'Hello, World!' > /var/tmp/hello-world.txt
Here, we are defining our cloud-init user-data in the
:ref:`#cloud-config <user_data_formats>` format, using the
:ref:`runcmd module <mod_cc_runcmd>` to define a command to run. When applied,
it will write ``Hello, World!`` to :file:`/var/tmp/hello-world.txt` (as we
shall see later!).
Launch a LXD container with our user-data
=========================================
Now that we have LXD set up and our user-data defined, we can launch an
instance with our user-data:
.. code-block:: shell-session
$ lxc launch ubuntu:focal my-test --config=user.user-data="$(cat /tmp/my-user-data)"
Verify that cloud-init ran successfully
-------------------------------------------
After launching the container, we should be able to connect to our instance
using:
.. code-block:: shell-session
$ lxc shell my-test
You should now be in a shell inside the LXD instance.
Before validating the user-data, let's wait for cloud-init to complete
successfully:
.. code-block:: shell-session
$ cloud-init status --wait
Which provides the following output:
.. code-block::
status: done
Verify our user-data
--------------------
Now we know that cloud-init ran successfully, we can verify that it
received the expected user-data we provided earlier:
.. code-block:: shell-session
$ cloud-init query userdata
Which should print the following to the terminal window:
.. code-block::
#cloud-config
runcmd:
- echo 'Hello, World!' > /var/tmp/hello-world.txt
We can also assert the user-data we provided is a valid cloud-config:
.. code-block:: shell-session
$ cloud-init schema --system --annotate
Which should print the following:
.. code-block::
Valid schema user-data
Finally, let us verify that our user-data was applied successfully:
.. code-block:: shell-session
$ cat /var/tmp/hello-world.txt
Which should then print:
.. code-block::
Hello, World!
We can see that cloud-init has received and consumed our user-data
successfully!
Completion and next steps
=========================
Exit the container shell (by typing :command:`exit` or pressing :kbd:`Ctrl-D`).
Once we have exited the container, we can stop the container using:
.. code-block:: shell-session
$ lxc stop my-test
We can then remove the container completely using:
.. code-block:: shell-session
$ lxc rm my-test
In this tutorial, we used the :ref:`runcmd module <mod_cc_runcmd>` to execute a
shell command. The full list of modules available can be found in our
:ref:`modules documentation<modules>`.
Each module contains examples of how to use it.
You can also head over to the :ref:`examples page<yaml_examples>` for
examples of more common use cases.
.. _LXD: https://ubuntu.com/lxd
.. _other installation options: https://documentation.ubuntu.com/lxd/en/latest/installing/#other-installation-options
|
