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Hi,

I have a Ussuri setup with 5 compute nodes (same resource spec).
When launch 5 Cirros VMs in a batch, they are all launched on
the same compute node. All 5 nodes have sufficient resource.

AWIK, Nova scheduler picks a compute randomly after going through
filtering. But 5 VMs all on the same compute is quite coincidental.
Could it be something missing?
Is there any control to such random pick?
Any way to make a better balancing?

>From the below log, could anyone let me know how compute-4 was
selected? I tried a few more launches, it's always compute-4
was selected.
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2020-10-27 13:56:45.484 24 DEBUG nova.scheduler.filter_scheduler [req-e2c6bf4b-7512-4ff0-9899-2a24bffa9131 113ee63a9ed0466794e24d069efc302c 32be191b3ec9497eaec108a22220890b - default default] Filtered [(compute-4, compute-4) ram: 131698MB disk: 14251008MB io_ops: 0 instances: 17, (compute-5, compute-5) ram: 232050MB disk: 14251008MB io_ops: 0 instances: 2, (compute-2, compute-2) ram: 367785MB disk: 14252032MB io_ops: 0 instances: 5, (compute-1, compute-1) ram: 298665MB disk: 14251008MB io_ops: 0 instances: 9, (compute-3, compute-3) ram: 259753MB disk: 14251008MB io_ops: 0 instances: 19] _get_sorted_hosts /usr/lib/python3.6/site-packages/nova/scheduler/filter_scheduler.py:443
2020-10-27 13:56:45.485 24 DEBUG nova.scheduler.filter_scheduler [req-e2c6bf4b-7512-4ff0-9899-2a24bffa9131 113ee63a9ed0466794e24d069efc302c 32be191b3ec9497eaec108a22220890b - default default] Weighed [WeighedHost [host: (compute-4, compute-4) ram: 131698MB disk: 14251008MB io_ops: 0 instances: 17, weight: 2.315526126088031], WeighedHost [host: (compute-2, compute-2) ram: 367785MB disk: 14252032MB io_ops: 0 instances: 5, weight: -999997.0], WeighedHost [host: (compute-1, compute-1) ram: 298665MB disk: 14251008MB io_ops: 0 instances: 9, weight: -999997.2171186721], WeighedHost [host: (compute-3, compute-3) ram: 259753MB disk: 14251008MB io_ops: 0 instances: 19, weight: -999997.3362949106], WeighedHost [host: (compute-5, compute-5) ram: 232050MB disk: 14251008MB io_ops: 0 instances: 2, weight: -999997.371492924]] _get_sorted_hosts /usr/lib/python3.6/site-packages/nova/scheduler/filter_scheduler.py:462
2020-10-27 13:56:45.486 24 DEBUG nova.scheduler.utils [req-e2c6bf4b-7512-4ff0-9899-2a24bffa9131 113ee63a9ed0466794e24d069efc302c 32be191b3ec9497eaec108a22220890b - default default] Attempting to claim resources in the placement API for instance ac10e5df-7e55-4c88-a682-df25cb6dd535 claim_resources /usr/lib/python3.6/site-packages/nova/scheduler/utils.py:1175
2020-10-27 13:56:45.657 24 DEBUG nova.scheduler.filter_scheduler [req-e2c6bf4b-7512-4ff0-9899-2a24bffa9131 113ee63a9ed0466794e24d069efc302c 32be191b3ec9497eaec108a22220890b - default default] [instance: ac10e5df-7e55-4c88-a682-df25cb6dd535] Selected host: (compute-4, compute-4) ram: 131698MB disk: 14251008MB io_ops: 0 instances: 17 _consume_selected_host /usr/lib/python3.6/site-packages/nova/scheduler/filter_scheduler.py:354
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Thanks!
Tony