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

[Thomas Goirand]

On 02/08/2013 12:55 AM, Thomas Goirand wrote:
> 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

Oh, and I forgot. Yes, it seems you can actually run Openstack and still
have XAPI based virtual machines... It's in fact the way to go to setup
Openstack with XCP: you would run a virtual machine that holds the
openstack compute daemon, which talks to XAPI through it's plugin.

Cheers,

Thomas