kvm instance creation

[Michael Foord]

On 03/06/15 09:15, Robie Basak wrote:
> Hi Michael,
>
> (uvtool author here)
>
> On Tue, Jun 02, 2015 at 09:30:15AM +0100, Michael Foord wrote:
>> In order to specify a MAC address for a KVM image we need to create a
>> libvirt domain xml template to pass as the template argument to uvt-kvm.
> Right.
>
>> Ideally we'd like to specify as *little as possible* in the template and
>> have the generated libvirt xml (i.e. the created image) be identical to what
>> uvt-kvm would have created for us without the template. The only change
>> being that the image will have a network interface with the MAC address we
>> specify.
>>
>> Attached are two xml files. "juju-bare-metal.xml" is the *generated* xml
>> (using master) for a kvm image on MAAS bare metal (functionally the same as
>> the xml we generate for a kvm image in a kvm image - I checked).
>> "template.xml" is the minimal template I found that would cause uvt-kvm to
>> generate the same image.
> What you've done here is correct the best way to do it right now - I
> presume you will end up generating the XML here instead of letting
> uvtool do it?

We have a minimal template, specifying only what we have to, and let 
uvtool generate the rest from defaults and command line parameters.

> Note that in addition to picking up the (usually default) template XML
> file, uvtool also does some manipulation of the XML tree in response to
> the other options specified (--disk, --memory, some networking options,
> etc) as well as some mandatory manipulations (defining the name, for
> example).
Yes, we'll still be using the command line parameters for those things. 
We'd like to hardcode as little as possible in the XML for the reasons 
you describe.

> One catch is that if things change in the future, Juju (by hardcoding
> the XML default) will be stuck in the past. For example, I think there
> are some changes in the pipeline where supporting different
> architectures such as ppc64el and arm64 require slightly different
> optimal XML definitions.
>
> How about I add an option to allow you to set the MAC address from the
> command line? This would only apply to >= Wily, but older releases
> aren't set to change anyway. For future releases, if you used that
> option, then you'd get what you need but also be able to stick to
> default XML handling.
>
> The catch is that you'll need to implement it both ways - but the
> implementation to add the command line option would presumably be pretty
> small.
>
> How does that sound?

That would be great! We're happy to use XML generation as a fallback for 
older versions of uvtool.

At some point in the not too far future we'll need to support multiple 
NICs (each with a MAC address and bridged to a different network on the 
host), so if you could bear that use case in mind that would also be 
great...

Many thanks,

Michael Foord

> Robie
>
>

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