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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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