[Openstack-operators] [Nova][Scheduler] How to filter and pick Host with least number of instances.

Mikhail Medvedev mihailmed at gmail.com
Mon Oct 10 13:02:19 UTC 2016


On Thu, Oct 6, 2016 at 10:26 PM, Karan <digitalkaran at gmail.com> wrote:
> Thanks Mikhail for mentioning custom wieghter. Sure I would like to
> look at how you've implemented your own weighter. Please share it when
> you've it with you.

See [1] for a very simple implementation.

> Also, it would be helpful if you can give
> pointers on implementing your weighter based on different  metrics of
> hosts.

You can look into what is available through host_state variable if you
need to weigh based on something else. See [2] (seems out of date).
You can also look/grep through nova scheduler source code.

[1] https://github.com/mmedvede/scheduler-weights
[2] https://wiki.openstack.org/wiki/Nova-scheduler-HostState

>
> On Wed, Oct 5, 2016 at 4:11 PM, Mikhail Medvedev <mihailmed at gmail.com> wrote:
>> Hi Karan,
>>
>> On Sep 22, 2016 19:19, "Karan" <digitalkaran at gmail.com> wrote:
>>>
>>> Hi
>>>
>>> Is it possible to configure openstack scehduler to schedule instances
>>> to a host with least number of instances running on it?
>>> When multiple hosts are eligible to spawn a new instance, scheduler
>>> applies weight multipliers to available RAM and CPU and pick one host.
>>> Is there a way to ask scheduler to pick a Host with least number y of
>>> instances on it.
>>>
>>
>> Yes, there is a way to select a host with the least number of instances. It
>> can be done by writing a custom weighter that returns negated number of
>> instances as host weight. I wrote an implementation that has been used for a
>> while in our test cloud, but I am not going to be able to share it until
>> next week. Let me know if you still need it by then.
>>
>>>
>>> Thanks
>>> Karan
>>>
>>> _______________________________________________
>>> OpenStack-operators mailing list
>>> OpenStack-operators at lists.openstack.org
>>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
>>
>> --
>> Mikhail Medvedev (mmedvede)
>> IBM, OpenStack CI for KVM on Power



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