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Managing my virtual machines
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I have a laptop with 16 GiB RAM, which is enough to run a few virtual
machines. I make use of this to run VMs as, for example, workers for
my CI setup, such that I have two or three versions of Debian
(oldstable, stable, unstable) and two CPU architectures (i386, amd64).
This lets me test the software I develop on a large fraction of the
environments in which my users run it on.
I have a few other VMs as well. Managing all of these would be tricky,
but I've gathered some tools for this:
* The actual virtualisation is KVM, managed by libvirt. This is less
invasive than running OpenStack of similar cloud services on my
laptop.
* I use Ansible for configuration management. It's easy to use, and
doesn't require Ruby or running an agent on each machine.
* I create each VM from a base image. The base images are created by
vmdebootstrap, a tool I wrote and that Neil Williams now maintains.
The base images have a minimal install, with a user `ansible` that
is allowed passwordless sudo, and an `authorized_keys` file that
allows my Ansible to log into them and do things.
The creation of a new VM is a somewhat intricate process:
* Create a new LV of the same size as the base images.
* Unpack the correct base image onto the LV. The base images are
stored compressed in an archive location.
* Create the VM, with `virt-install`. This chooses a random MAC
address for the new VM, and also starts it.
* Find the new VM's MAC address in the
`/var/lib/libvirt/dnsmasq/default.leases` file, and pick out the IP
address given to it.
* Add to `/etc/hosts` a line that gives the VM's IP address a name
that's the new VM's hostname.
All of the above is automated into a script.
After this, the new VM can be managed by Ansible. Ansible gets run
manually after the VM creation script, and after I've added the new VM
to my Ansible config.
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