KVM - VM Templates

It has been a minute since I had done any KVM based VMs so I wanted to share some little tidbits on creating your KVM templates. I will be focusing on Debian/Ubuntu here for now so YMMV.

Update: 01/07/2017 - CentOS added

First, let’s install a few pre-req packages:

sudo apt-get install -y virtinst libosinfo-bin libguestfs-tools virt-top

Below is a shell script that I have created which will allow me to provision my baseline template easily. You will need to adjust based on your needs. I am using br0 for my NETWORK_BRIDGE which allows me to connect directly to my external network rather than a default NAT connection. So you may want to use the built-in default virbr0 instead.

Below are preseed files which work for Ubuntu 16.04 and Debian Jessie as they are based on systemd and on reboot using virsh console the login prompt is enabled to work correctly. That bit of magic works in the late_command section at the end. You will also want to change the default user and password as they are defined as ubuntu/ubuntu and debian/debian.

And this little script can be executed within your VM in order to prep it to be used as a template by cleaning up some important things. Or better yet, if you look closely at the above preseed files I have included those important cleanup steps in the late_command steps, so you do not have to run this script at all if you use the preseed files.

So how do we wrap all of this up into an easy format to consume? You can quite simply copy/paste the script and appropriate preseed file into your folder structure that you use. Make sure to name the preseed file as preseed.cfg otherwise it will not work with virt-install. Also, make sure to modify the variables for *DISK_PATH,* PRESEED_FILE, and NETWORK_BRIDGE as appropriate. And once you have completed that you are ready to run the script and watch the VM build and get ready for template usage. Also note, that when using the preseed file with our script, the VM will actually shutdown at the end of the installation. This is the desired state as we want everything including our non-generated SSH keys to be clear for template usage.

Build template:

chmod +x libvirt_install_vm.sh
sudo ./libvirt_install_vm.sh

Clone template (Note: Replace OURNEWVM with the name you desire for the cloned VM):

sudo virt-clone -o ubuntu1604 -n OURNEWVM -f /var/lib/libvirt/images/OURNEWVM.qcow2
sudo virsh start OURNEWVM --console

And there you have it. A new shiny KVM based Ubuntu template ready for cloning. Stay tuned as I will be taking this process further with some Ansible automation to fully deploy and etc.

Update: CentOS Info

Below you will find the script and ks.cfg files to use with CentOS.

Enjoy!