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

[Daniel Pocock]

On 07/02/13 17:58, Thomas Goirand wrote:
> 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.
>>
>>     

This first option may eliminate the need to worry about the second
option (below), as it suggests that all the existing VPSes could simply
be converted to volumes under the control of Cinder.  Does that make sense?

When I went looking for details, I found one bug, which looks like it is
just an inconvenience, booting such a VM requires a (real or dummy)
image to exist in Glance even if it is not used:
https://bugs.launchpad.net/nova/+bug/1008622


>>> 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
>>     

This is the use case I'm thinking of - people who have a collection of
VMs created in the days of lenny or squeeze and want to start
introducing OpenStack to their environment.

Everything I read about OpenStack seems to be aimed at greenfield
projects with a budget to buy new servers.

>> 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.
>>
>>     
The installations I am thinking about right now are all Xen, so this is
something I need to look at in more depth.

Could you comment on the same problem from a KVM perspective?  E.g. if
somebody has a vanilla KVM environment (or they convert their Xen
environment to KVM), then they can bring in OpenStack and start running
Nova on some of those boxes?

>> 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.
>
>   
Is such a hybrid setup likely to cause other headaches though?

For example, when OpenStack adjusts iptables or ethernet bridge
configuration, does that have any side-effects for existing VMs or VPSes
on the same box?  Or they can happily co-exist and it won't change their
networking?

I've had a good look at the proposition from Ubuntu, they make it all
look very easy on their quick start guide and their marketing materials
and it would be good to see a Debian alternative to this.  I think that
demonstrating a migration path for existing Debian users will be a
helpful part of this, because it will bring more Debian-minded people
into the OpenStack community.

Regards,

Daniel