Open Stack

----- Original Message -----
> From: "Sangeeta Singh" <singhs at yahoo-inc.com>
> To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
> Sent: Wednesday, March 26, 2014 6:54:18 PM
> Subject: Re: [openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..
> 
> 
> 
> On 3/26/14, 10:17 AM, "Khanh-Toan Tran" <khanh-toan.tran at cloudwatt.com>
> wrote:
> 
> >
> >
> >----- Original Message -----
> >> From: "Sangeeta Singh" <singhs at yahoo-inc.com>
> >> To: "OpenStack Development Mailing List (not for usage questions)"
> >><openstack-dev at lists.openstack.org>
> >> Sent: Tuesday, March 25, 2014 9:50:00 PM
> >> Subject: [openstack-dev] [nova][scheduler] Availability Zones and Host
> >>aggregates..
> >> 
> >> Hi,
> >> 
> >> The availability Zones filter states that theoretically a compute node
> >>can be
> >> part of multiple availability zones. I have a requirement where I need
> >>to
> >> make a compute node part to 2 AZ. When I try to create a host aggregates
> >> with AZ I can not add the node in two host aggregates that have AZ
> >>defined.
> >> However if I create a host aggregate without associating an AZ then I
> >>can
> >> add the compute nodes to it. After doing that I can update the
> >> host-aggregate an associate an AZ. This looks like a bug.
> >> 
> >> I can see the compute node to be listed in the 2 AZ with the
> >> availability-zone-list command.
> >> 
> >
> >Yes it appears a bug to me (apparently the AZ metadata indertion is
> >considered as a normal metadata so no check is done), and so does the
> >message in the AvailabilityZoneFilter. I don't know why you need a
> >compute node that belongs to 2 different availability-zones. Maybe I'm
> >wrong but for me it's logical that availability-zones do not share the
> >same compute nodes. The "availability-zones" have the role of partition
> >your compute nodes into "zones" that are physically separated (in large
> >term it would require separation of physical servers, networking
> >equipments, power sources, etc). So that when user deploys 2 VMs in 2
> >different zones, he knows that these VMs do not fall into a same host and
> >if some zone falls, the others continue working, thus the client will not
> >lose all of his VMs. It's smaller than Regions which ensure total
> >separation at the cost of low-layer connectivity and central management
> >(e.g. scheduling per region).
> >
> >See: http://www.linuxjournal.com/content/introduction-openstack
> >
> >The former purpose of regouping hosts with the same characteristics is
> >ensured by host-aggregates.
> >
> >> The problem that I have is that I can still not boot a VM on the
> >>compute node
> >> when I do not specify the AZ in the command though I have set the
> >>default
> >> availability zone and the default schedule zone in nova.conf.
> >> 
> >> I get the error ³ERROR: The requested availability zone is not
> >>available²
> >> 
> >> What I am  trying to achieve is have two AZ that the user can select
> >>during
> >> the boot but then have a default AZ which has the HV from both AZ1 AND
> >>AZ2
> >> so that when the user does not specify any AZ in the boot command I
> >>scatter
> >> my VM on both the AZ in a balanced way.
> >> 
> >
> >I do not understand your goal. When you create two availability-zones and
> >put ALL of your compute nodes into these AZs, then if you don't specifies
> >the AZ in your request, then AZFilter will automatically accept all hosts.
> >The defaut weigher (RalWeigher) will then distribute the workload fairely
> >among these nodes regardless of AZ it belongs to. Maybe it is what you
> >want?
> 
>   With Havana that does not happen as there is a concept of
> default_scheduler_zone which is none if not specified and when we specify
> one can only specify a since AZ whereas in my case I basically want the 2
> AZ that I create both to be considered default zones if nothing is
> specified.

If you look into the code of the AvailabilityFilter, you'll see that the filter automatically accepts host if there is NO availability-zone in the request, which is the case when user does not specify AZ. This is exactly what I see in my Openstack platform (Hanava stable). FYI, I didn't set up a default AZ in config. So whenever I creates several VMs without specifying an AZ, the scheduler spreads the VMs into all hosts regardless of their AZ.

What I think lacking is that user can not select a set of AZs instead of one or none right now.

> >
> >> Any pointers.
> >> 
> >> Thanks,
> >> Sangeeta
> >> 
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> >> OpenStack-dev at lists.openstack.org
> >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> >>
> >
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