While discussing the proposal to add resource_class' to Ironic nodes for
interacting with the resource provider system in Nova with Jim on IRC, I voiced
my concern about having a resource_class per node. My thoughts were that we
could achieve the behaviour we require by every Ironic node resource provider
having a "baremetal" resource class of which they can own a maximum of 1.
Flavor's that are required to land on a baremetal node would then define that
they require at least 1 baremetal resource, along with any other resources they
require. For example:
Resource Provider 1 Resources:
Baremetal: 1
RAM: 256
CPUs: 4
Resource Provider 2 Resources:
Baremetal: 1
RAM: 512
CPUs: 4
Resource Provider 3 Resources:
Baremetal: 0
RAM: 0
CPUs: 0
(Resource Provider 3 has been used, so it has zero resources left)
Given the thought experiment it seems like this would work great with one
exception, if you define 2 flavors:
Flavor 1 Required Resources:
Baremetal: 1
RAM: 256
Flavor 2 Required Resources:
Baremetal: 1
RAM: 512
Flavor 2 will only schedule onto Resource Provider 2 because it is the only
resource provider that can provide the amount of resources required. However
Flavor 1 could potentially end up landing on Resource Provider 2 even though it
provides more RAM than is actually required. The Baremetal resource class would
prevent a second node from ever being scheduled onto that resource provider, so
scheduling more nodes doesn't result on 2 instance on the same node, but it is
an inefficient use of resources.
To combat this inefficient use of resources, I wondered if it was possible to
add a flag to a resource provider to define that it is an indivisible resource
provider, which would prevent flavors that don't use up all the resources a
provider provides from landing on that provider.
Sam
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