Comment 9 for bug 1609193

Per comment 7, the scheduler claims resources in placement since pike but that still doesn't resolve this issue, see bug 1790204. The resource tracking code is not smart enough to consider that the instance is being resized on the same host where it's already consuming resources and count those as available, so in this case you start with VCPU=1 and want to go to VCPU=4, there are 4 total VCPU on the host. nova/placement is going to try to claim 4 when there are only 3 available and fail. See my attempts at fixing bug 1790204 - this isn't going to be fixed anytime soon and I think is best documented as a known limitation.