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

Sangeeta Singh singhs at yahoo-inc.com
Wed Mar 26 23:16:30 UTC 2014


To update the thread the initial problem that I mentioned that when I add a host to multiple availability zone(AZ) and then do a
“nova boot” without specifying a AZ expecting the default zone to be picked up.

This is due to the bug [1] as mentioned by Vish. I have updated the bug with the problem.

The validation fails during instance create due to the [1]


[1] https://bugs.launchpad.net/nova/+bug/1277230
From: Sylvain Bauza <sylvain.bauza at gmail.com<mailto:sylvain.bauza at gmail.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 1:34 PM
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 can't agree more on this. Although the name sounds identical to AWS, Nova AZs are *not* for segregating compute nodes, but rather exposing to users a certain sort of grouping.
Please see this pointer for more info if needed : http://russellbryantnet.wordpress.com/2013/05/21/availability-zones-and-host-aggregates-in-openstack-compute-nova/

Regarding the bug mentioned by Vish [1], I'm the owner of it. I took it a while ago, but things and priorities changed so I can take a look over it this week and hope to deliver a patch by next week.


[1] https://bugs.launchpad.net/nova/+bug/1277230

2014-03-26 19:00 GMT+01:00 Chris Friesen <chris.friesen at windriver.com<mailto:chris.friesen at windriver.com>>:
On 03/26/2014 11:17 AM, Khanh-Toan Tran wrote:

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.

See Vish's email.

Even under the original meaning of availability zones you could realistically have multiple orthogonal availability zones based on "room", or "rack", or "network", or "dev" vs "production", or even "has_ssds" and a compute node could reasonably be part of several different zones because they're logically in different namespaces.

Then an end-user could boot an instance, specifying "networkA", "dev", and "has_ssds" and only hosts that are part of all three zones would match.

Even if they're not used for orthogonal purposes, multiple availability zones might make sense.  Currently availability zones are the only way an end-user has to specify anything about the compute host he wants to run on.  So it's not entirely surprising that people might want to overload them for purposes other than physical partitioning of machines.


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