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[Chris Behrens <chris.behrens@xxxxxxxxxxxxx>]

I have some plans for being able to set arbitrary "capabilities" for hosts via nova.conf that you can use to build scheduler filters.

Right now, there are capabilities, but I believe we're only creating these from hypervisor stats.  You can filter on those today.  What I'm planning on adding is a way to specify additional keyname/value pairs in nova.conf to supplement the capabilities we build from hypervisor stats.  You could set things like this in your nova.conf:

--host_capabilities=instance_type_ids=1,2,3;keyX;keyY=something

etc.  Since capabilities are already passed to scheduler rules, you could add some basic filters that do:

if 'instance_type_ids' in capabilities and instance_type.id not in capabilities['instance_type_ids']:
    return False

Since host_capabilities are just arbitrary keyname/value pairs, you can pretty much add anything you want to --host_capabilities and then write some matching scheduler filter rules.

That's the basic idea, anyway.   The exact same behavior will apply to 'cells' and the cells scheduler as well.  (Except you'll have cells_capabilities=  somewhere (prob nova.conf for the cells service).

- Chris


On Apr 2, 2012, at 10:36 AM, Day, Phil wrote:

Hi Folks,

I’m looking for a capability to limit some flavours to some hosts.  I want the mapping to be as flexible as possible, and work within a zone/cell  (I don’t want to add zones just to get this mapping).    For example I want to express something like:

Host_1 supports flavours A, C
Host_2 supports flavours A, B
Host_3 supports flavours A, B, C
Host_4 supports flavours D

Ideally there would be some form of grouping to sets of flavours:

Flavour_A  is part of Flavour_Sets 1, 2, 3
Flavour_B is part of Flavour_Sets 2, 3
Flavour_C is part of Flavour_Sets 1, 3, 4

Host_1 supports flavour Set 1
Host_2 supports flavour Set 2
Host_3 supports flavour Set 3
Host_4 supports flavour Set 4


>From the Essex design summit I thought that host aggregates was going to give this sort of capability, but having looked through the code that seems to be quite tightly coupled with specific hypervisor functionality, whereas this is purely a scheduler feature.

I can see that I could define flavour group membership through the instanace_type_extra_specs, but not how to then associate these with specific hosts.

I know I’m a tad behind some of the recent changes – so before suggesting a design summit session on this I thought I’d ask - is there something that already does this type of mapping ?

Cheers,
Phil



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