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Hi all,
    I'd appreciate if the experts can point me in one direction or another. If there are existing mechanisms, we don't want to reinvent the wheel. If there aren't, I'd be interested in exploring clean ways to extend and enhance nova scheduling.

Thank you very much.

Cheers,
Sundar

From: Sundar Nadathur
Sent: Monday, August 24, 2015 10:48 PM
To: 'openstack-dev at lists.openstack.org'
Subject: [Nova] Placing VMs based on multiple criteria

Hi,
   Please advise me whether the following scenario requires changes to nova scheduler or can be handled with existing scheduling mechanisms.

I have a type of PCIe device (not necessarily a NIC or HBA). The device can be configured with a set of user-defined resources - say A, B, C. Each resource can be shared between a limited number of VMs -- say A can be shared among 4 VMs, B among 8, etc. A VM image may request the need for a specific list of features, say A and B. Then I want to place the VM on a host according to these criteria:

1.       If there are hosts with a PCIe device that already has A and B configured, and has a free instance each of A and B, the VM  must be placed on one of those hosts.

2.       Otherwise, find a host with this PCIe device that can be configured with one instance each of A and B.

It is not clear that this can be handled through 3rd party metadata. Suppose we create host aggregates with properties like "resource=A" and "resource=B", and also associate properties like "resource=A" with VM images. (A and B are UUIDs representing user-defined resources.) Perhaps Nova scheduler can match the properties to select host aggregates that have all properties that the VM requires. However:

a.       This would not be dynamic (i.e. track the free instances of each resource), and

b.      This addresses only #1 above.

Is there any way I can leverage existing scheduler mechanisms to  solve this VM placement problem? If not, do you have thoughts/comments on what changes are needed?

Thanks, and apologies in advance if I am not clear. Please feel free to ask questions.

Cheers,
Sundar

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