Related to our disposable clients initiative in Taskotron, I'm working on ways
how to boot and manage those clients. In order to know how to boot them, I need
to know how they are created (e.g. cloud images require special magic with
cloud-init). That's why I spent some time in the past looking at different ways
how to either create custom images or re-use existing ones. The simplest
approach turned out to be (in my view) a tool called virt-builder. It's a part
of libguestfs project and it's a super easy way to create Fedora disk images -
they have them already pre-created and stored on the server, so it just
downloads them and customize them a little bit per your requirements:
$ virt-builder fedora-21 --root-password password:fedora --install vim-enhanced
--update
I decided to try to use it for creating the base image for our disposable
clients. The idea is that virt-builder is run once a day on a server and it
generates a fresh new VM disk image. We then use this disk image for all our
disposable clients spawned in the future, until a new disk image is generated
the next day. Rinse and repeat.
The benefit of this approach (over e.g. official cloud images which might be
updated once per month or twice per year) is:
* the clients are always up-to-date
* it's very light on bandwidth - instead of downloading updates for every
client on every task run, it's done once per day, centrally
* it's much faster - the clients just boot and execute the task, they don't
spend time upgrading each boot
* it's less error-prone - there is a never-ending story of failures when you
communicate over network thousands times per day. We know it really well. By
updating the client just once, the chance for a network error is much lower,
and we can easily repeat it if it fails. Also, it's not a big deal if it
completely fails some day, our tasks continue to be executed without a problem,
just with a day-old packages installed.
* can be integrated with fedmsg "updates pushed" notification to be almost
instantly in sync with the latest updates
* it helps with rescheduling tasks and reproducing issues - if we keep last
X-number of VM images, we can easily replay past tasks with exactly the same
package set as it had during that time
Subsequently I realized that we will probably also want to have several
different base disk images, not just one. For example, certain GNOME checks
might require most of GNOME installed, which would mean downloading a lot of
packages every time they are run. But with virt-install, we can pre-create
different base images for different purposes, and then let the task define
which image to use. So for GNOME checks, we would prepare a base image with
full GNOME installed.
To make all of this manageable, I created a wrapper around virt-builder and
called it taskotron-vmbuilder (ideas for a better name are welcome). The code
is available here:
https://bitbucket.org/fedoraqa/taskotron-vmbuilder
The concept is that you can define templates and then run vmbuilder which takes
care of the rest - it uses virt-builder to create the image, it makes sure that
libtaskotron is installed, it configures stuff like root password and ssh key.
We can add any other functionality that is needed. The simplest way to try this
is this:
$ ./vmbuilder.py templates/f21-minimal.yaml
There are sample templates for minimal installation and Server and Workstation
products. For more details, look into READMEs, it's fairly well documented, I
think. My idea is that we will run this daily on the server, store the
resulting images somewhere, and update the pointer to the "current one".
I still haven't created project and repo in Phab, but if you approve this as a
way forward, I will.
Thanks,
Kamil
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