Nova/SchedulingBasedOnInstanceResourceQuota

Problem

Operator wants Nova scheduler take Instances with resource quota enable into account.

Overview

Nova provides the ability to set CPU time consumption percent for instances https://wiki.openstack.org/wiki/InstanceResourceQuota. For instance, setting Quota/Period with a ratio of 1/6 will result in instances using 1/6 of vcpu. We need to find a way for the scheduler to take this into account during scheduling.

Proposals

Isolated aggregate

A first solution could be to reserve some specific hosts for a particular flavor and then configuring cpu allocation with the desired ratio.

How to use it

Work with Havana
For a flavor with a resource limited to 1/6 vcpu

Configure the scheduler with filters 'AggregateCoreFilter' and 'AggregateInstanceExtraSpecFilter'
Create a flavor and set the 'aggregate_instance_extra_specs:flavor_type' metadata to 'tiny_flavor' (or another value)
Create an aggregate to isolate a resource limited flavor and set the 'cpu_allocation_ratio' metadata of this aggregate to 6.
Set the 'flavor_type' metadata of this aggregate to 'tiny_flavor'

Problems

Dedicated hosts for flavor: host provisioning.
Impact of important number of VMs per host: workload density (to be studied with Neutron/Nova).
What about other drivers? currently only libvirt support this feature.

Add new metric `cpu_used`

To be discussed in the community