Comment 2 for bug 1742747

The problem is actually more complicated now due to the issue detailed in this thread:

http://lists.openstack.org/pipermail/openstack-operators/2018-January/014748.html

I believe what we will need to do is change the behaviour of the RT when the nova-compute's nova.conf CONF.cpu_allocation_ratio is 0.0 we should look up the value of the first host aggregate the compute node belongs to and look for a cpu_allocation_ratio metadata key, and if found, use that.

For the cases when no host aggregates exist or no cpu_allocation_ratio metadata key exists for a host aggregate associated to the compute node, then the defaults should follow the policy that is documented in the configuration option already:

https://github.com/openstack/nova/blob/master/nova/conf/compute.py#L416-L421