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.. _lxd_tutorial:
Tutorial
********
In this tutorial, we will create our first cloud-init user data script
and deploy it into an LXD container. 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 for quick
testing and iterating on our user data definition.
Setup LXD
=========
Skip this section if you already have LXD_ setup.
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`_.
Initialize LXD
--------------
.. code-block:: shell-session
$ lxd init --minimal
The minimal configuration should work fine for our purposes. It can always
be changed at a later time if needed.
Define our user data
====================
Now that LXD is setup, we can define our user data. Create the
following file on your local filesystem at ``/tmp/my-user-data``:
.. 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<topics/format:Cloud Config Data>` format, using the
`runcmd`_ module to define a command to run. When applied, it
should write ``Hello, World!`` to ``/var/tmp/hello-world.txt``.
Launch a container with our user data
=====================================
Now that we have LXD setup 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
.....
cloud-init status: done
$
We can now verify that cloud-init received the expected user data:
.. code-block:: shell-session
$ cloud-init query userdata
#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
Valid cloud-config: system userdata
$
Finally, verify that our user data was applied successfully:
.. code-block:: shell-session
$ cat /var/tmp/hello-world.txt
Hello, World!
$
We can see that cloud-init has consumed our user data successfully!
Tear down
=========
Exit the container shell (i.e., using ``exit`` or ctrl-d). Once we have
exited the container, we can stop the container using:
.. code-block:: shell-session
$ lxc stop my-test
and we can remove the container using:
.. code-block:: shell-session
$ lxc rm my-test
What's next?
============
In this tutorial, we used the runcmd_ module to execute a shell command.
The full list of modules available can be found in
:ref:`modules documentation<modules>`.
Each module contains examples of how to use it.
You can also head over to the :ref:`examples<yaml_examples>` page for
examples of more common use cases.
.. _LXD: https://linuxcontainers.org/lxd/
.. _other installation options: https://linuxcontainers.org/lxd/getting-started-cli/#other-installation-options
.. _runcmd: https://cloudinit.readthedocs.io/en/latest/topics/modules.html#runcmd
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