AggregateCoreFilter replacement options

Issue

AggregateCoreFilter allows defining a cpu allocation ratio for a set of compute hosts that are part of an aggregate. It is used in conjunction with nova.conf parameter vcpu_pin_set, which specifies on each compute host the cores that are selected to act as (shared) vcpus. These shared vcpus can be over allocated as specified by the cpu allocation ratio.

AggregateCoreFilter and vcpu_pin_set have been deprecated in OSP16.x.

vcpu_pin_set is being replaced with cpu_dedicated_set and cpu_shared_set parameters, and two separate options are proposed to provide equivalent functionality to the AggregateCoreFilter.

The first option is to define cpu allocation ratios per host in nova.conf, for each compute host that is part of the aggregate. Keep in mind that this option, although simple to implement, removes some flexibility in operations. Take for example, a situation where same role and options are implemented on 2 separate compute hosts,and each host is used by a separate tenant. Then if one tenant needs to change allocation ratios, operator will need to undeploy the node, create new role, and redeploy with this new role. This will require a maintenance window, migrating instances back and forth, etc.

The second option that is proposed is to define aggregate cpu allocation ratios via the placement API. This option is a bit more elaborate to set up, and is described in details in the Resolution section below.

Note that in OSP 17, management of resource provider information in the Placement API is facilitated through the use of config files, see Managing Resource Providers Using Config Files.