How to update a (VM) template?

[proxwolfe]

Hi,

I created a VM, installed the OS, added docker and made it all a template. From this template, I have spawned numerous new VMs. Apart from the fact that they all share the same fingerprint for SSH, this works fine for me.

But the older the template gets, the more updates I need to run in every new VM I spawn from it.

Now what I can do is, make a new VM from it, update it and make a new template and delete the old one.

But might there be a quicker, more elegant way to do update my template? Or is this the best practice?

Thanks

 

[fiona]

Hi,
you can create a full clone from the template, update that, and convert it to template again. If the other VMs spawned from the old template are linked clones, the original template still needs to be kept around (because the VMs disks will reference the disk of the original template then). Otherwise, you can remove the old template afterwards.

 

[proxwolfe]

you can create a full clone from the template, update that, and convert it to template again.

Thanks - that's exactly what I am doing:

Now what I can do is, make a new VM from it, update it and make a new template and delete the old one.

I just find this cumbersome and was wondering whether there might be a more elegant, potentially more automated, way to achieve the same result.

 

[fiona]

I just find this cumbersome and was wondering whether there might be a more elegant, potentially more automated, way to achieve the same result.

In theory, it could be supported to temporarily start a template if there are no linked clones. But it's at odds with the design: templates are supposed to be static (the disks are even marked as immutable on storages that support it), and they are very often used for linked clones.

 

[sabrtooth]

The best idea I've come across implemented was a template with updates scripted into it, so each clone has the script running keeping them current.

Every so often -- when the admin feels updates from the base take too long, they clone the base template, update it, and make a new clone with the update-to date in the name. All new VMs are made off of this.

It has it's pro's and cons but it was something that may help you. I liked how one template mistake couldn't crash the whole tree (been there), but I also recognize that, at somepoint, the oldest vms will have to be migrated to a newer template (I feel this is natural anyway)

 

[traxeon]

Take a look at virt-customize (https://libguestfs.org/virt-customize.1.html) and virt-edit packages from libguestfs (https://libguestfs.org/). I use virt-customize inside my ansible scripts to build my cloud-init images to pre-install the qemu agent on my linux machines and some other tools required for automated discovery. I almost use debian exclusively for all my vms.

virt-customize -a /path/to/templateimage.qcow2 --install qemu-guest, sudo

-- update is also available