[openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..

Sangeeta Singh singhs at yahoo-inc.com
Wed Mar 26 17:32:20 UTC 2014

From: <Baldassin>, Santiago B <santiago.b.baldassin at intel.com<mailto:santiago.b.baldassin at intel.com>>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Date: Wednesday, March 26, 2014 at 5:17 AM
To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org<mailto:openstack-dev at lists.openstack.org>>
Subject: Re: [openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..

I would say that the requirement is not valid. A host aggregate con only have one availability zone so what you actually can have is a compute node that’s part of 2 host aggregates, which actually have the same availability zone.

It is in our case where we have a superset host aggregate that has all the hosts and then we have subset host aggregates(AZ) based on PDU. Need is that our user can specify the AZ based on the PDU but also in case no AZ is specified we want to load balance from the superset which contains two host-aggregates(AZ).

In the scenario you mentioned below where you create the aggregates without associating the availability zone, after updating the aggregates with the zones, the hosts still share the same availability zone right?

No the host becomes part of two availability zones one for each of the host aggregates.

From: John Garbutt [mailto:john at johngarbutt.com]
Sent: Wednesday, March 26, 2014 8:47 AM
To: OpenStack Development Mailing List
Subject: Re: [openstack-dev] [nova][scheduler] Availability Zones and Host aggregates..

Sounds like an extra weighter to try and balance load between your two AZs might be a nicer way to go.

The easiest way might be via cells, one for each AZ . But not sure we merged that support yet. But there are patches for that.

On 25 Mar 2014 20:53, "Sangeeta Singh" <singhs at yahoo-inc.com<mailto:singhs at yahoo-inc.com>> wrote:

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.

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 “ERROR: The requested availability zone is not available”

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.

Any pointers.


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