Nodepool serializes all queries to OpenStack API in a queue which is processed once every rate seconds. It is currently set at a rate of 6 seconds or 10 queries per minute.
That delay operations such as building or deleting instances. We can experiment lowering it a bit to a rate of 5 seconds or 12 queries per minute. Then even go lower than that if the cloud infrastructure supports it.
Self note: git log --format=fuller -p -Grate: modules/nodepool/templates/nodepool.yaml.erb
In August 2016 we experimented a quota issue that caused Nodepool to spam the OpenStack infrastructure with queries it could not honor. Namely trying to boot new instance when the quota was considered full. The rate was set from 1 to 10 again ( T143016 - a82ffc941aeae8da623199761d8731db8a5f7d2b ).
It is currently at six since 4f499c3257f79037c2f9152519d9c90f55479c49
Thing to watch
During busy hours, Nodepool would effectively send queries at the maximum rate. That might cause issue on the Nova API and or the labvirt nodes if too many instances get spawned/deleted at once.