[openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..
sylvain.bauza at bull.net
Thu Mar 27 10:05:22 UTC 2014
Le 27/03/2014 10:37, Khanh-Toan Tran a écrit :
> ----- 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
>>>> 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.
That's because this is not the goal of this filter to exclude AZs if
none specified ;-)
If you want to isolate, there is another filter responsible for this 
IMHO, a filter should still be as simple as possible. That's only
combination of filters which should match any needs.
>>>> Any pointers.
>>>> OpenStack-dev mailing list
>>>> OpenStack-dev at lists.openstack.org
>>> OpenStack-dev mailing list
>>> OpenStack-dev at lists.openstack.org
>> OpenStack-dev mailing list
>> OpenStack-dev at lists.openstack.org
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