Open Stack

On 18 April 2018 at 15:10, Dan Smith <dms at danplanet.com> wrote:
>> Thanks for the concern and fully under it , the major reason is
>> cloud-init doesn't have a hook or plugin before it start to read
>> config drive (ISO disk) z/VM is an old hypervisor and no way to do
>> something like libvirt to define a ISO format disk in xml definition,
>> instead, it can define disks in the defintion of virtual machine and
>> let VM to decide its format.
>>
>> so we need a way to tell cloud-init where to find ISO file before
>> cloud-init start but without AE, we can't handle that...some update on
>> the spec here for further information
>> https://review.openstack.org/#/c/562154/
>
> The ISO format does not come from telling libvirt something about
> it. The host creates and formats the image, adds the data, and then
> attaches it to the instance. The latter part is the only step that
> involves configuring libvirt to attach the image to the instance. The
> rest is just stuff done by nova-compute (and the virt driver) on the
> linux system it's running on. That's the same arrangement as your
> driver, AFAICT.
>
> You're asking the system to hypervisor (or something running on it) to
> grab the image from glance, pre-filled with data. This is no different,
> except that the configdrive image comes from the system running the
> compute service. I don't see how it's any different in actual hypervisor
> mechanics, and thus feel like there _has_ to be a way to do this without
> the AE magic agent.

Having briefly read the cloud-init snippet which was linked earlier in
this thread, the requirement seems to be that the guest exposes the
device as /dev/srX or /dev/cdX. So I guess in order to make this work:

* You need to tell z/VM to expose the virtual disk as an optical disk
* The z/VM kernel needs to call optical disks /dev/srX or /dev/cdX

> I agree with Mikal that needing more agent behavior than cloud-init does
> a disservice to the users.
>
> I feel like we get a lot of "but no, my hypervisor is special!"
> reasoning when people go to add a driver to nova. So far, I think
> they're a lot more similar than people think. Ironic is the weirdest one
> we have (IMHO and no offense to the ironic folks) and it can support
> configdrive properly.

I was going to ask this. Even if the contents of the disk can't be
transferred in advance... how does ironic do this? There must be a
way.

Matt
-- 
Matthew Booth
Red Hat OpenStack Engineer, Compute DFG

Phone: +442070094448 (UK)