[Openstack-devel] Volatile images and/or hybrid cloud use cases

[Thomas Goirand]

On 02/07/2013 02:36 AM, Daniel Pocock wrote:
> I'm just wondering if anyone can comment on the following two topics:
> 
> 
> a) volatile images - e.g. development servers where new packages are
> installed every few days and where the entire system state must be
> preserved on every reboot.  Can the whole image concept be bypassed and
> the entire instance runs from persistent storage?

The feature that you are looking for is called "boot from volume". Eg,
Cinder provides a block storage to your nova VM, which boots from it.
Then it's more or less like a VPS.

> b) hybrid deployments - e.g. if somebody already has 5 physical servers
> running VMs with a vanilla Xen hypervisor, can they add Nova to those
> servers and run some OpenStack managed VM instances alongside the
> standalone images?  Or do they need to move all the vanilla VMs onto 3
> servers and then just run Nova on the other 2?

Well, it all depends what you call "vanilla". Currently, Openstack
doesn't really work with just Xen through libvirt, there has been some
effort for that, but I'm really not sure how far it went.

To run Openstack with Xen, you need XAPI, otherwise called "XCP", which
I happen to also maintain in Debian (it's been in Wheezy for more than a
year now). So, if you are currently running Xen using the python-based
daemon with the "xm" commands, then you will need to switch to something
else (eg: using the "xe" OCaml based toolstack, rather than "xm" or even
"xl"). The management of virtual machines in this XAPI environment is
quite different from what you would be used to with "xm".

As for the state of XCP in Debian, it seems that people tend to run more
CentOS than Debian + XCP, and Citrix is pushing hard for their CentOS
appliance CD image rather than the Debian flavor. It's been more than 6
months they released XCP 1.6 (as a CentOS based ISO image), but nothing
is coming to update what we have in Debian. Probably this will change
later on if Citrix pushes to unify the source code they have: the Debian
package carries 42 patches !!! Most of these are of course written
directly from upstream, but that shows how much they need to rework
their CentOS based code so that it understand better how Debian works.
One of the thing I worked hard on last year was fixing all these
redhat-ismes that were embedded in upstream source code.

You will find many people running Openstack using the CentOS-based XCP,
but I haven't find many using Debian. However, I did run it!!! And I
have even worked out some Openstack plugin packages for XCP in Wheezy. I
haven't gone very far with it, I just tested that I could run some
instances, and it did work. However, I haven't tested networking, though
I don't see why it wouldn't work.

I hope the above answers your questions, if not please ask again,

Cheers,

Thomas