[openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..
khanh-toan.tran at cloudwatt.com
Thu Mar 27 09:37:15 UTC 2014
----- 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>
> >----- 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
> >> 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
> >> 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
> >> However if I create a host aggregate without associating an AZ then I
> >> 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
> >> availability zone and the default schedule zone in nova.conf.
> >> I get the error ³ERROR: The requested availability zone is not
> >> What I am trying to achieve is have two AZ that the user can select
> >> the boot but then have a default AZ which has the HV from both AZ1 AND
> >> so that when the user does not specify any AZ in the boot command I
> >> 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
> 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
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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