[openstack-dev] Can we use two nova schedulers at the same time?

Alex Glikson GLIKSON at il.ibm.com
Tue Aug 13 08:15:25 UTC 2013

There are roughly three cases.
1. Multiple identical instances of the scheduler service. This is 
typically done to increase scalability, and is already supported (although 
sometimes may result in provisioning failures due to race conditions 
between scheduler instances). There is a single queue of provisioning 
requests, all the scheduler instances are subscribed, and each request 
will be processed by one of the instances (randomly, more or less). I 
think this is not the option that you referred to, though.
2. Multiple cells, each having its own scheduler. This is also supported, 
but is applicable only if you decide to use cells (e.g., in large-scale 
geo-distributed deployments).
3. Multiple scheduler configurations within a single (potentially 
heterogeneous) Nova deployment, with dynamic selection of 
configuration/policy at run time (for simplicity let's assume just one 
scheduler service/runtime). This capability is under development (
https://review.openstack.org/#/c/37407/) , targeting Havana. The current 
design is that the admin will be able to override scheduler properties 
(such as driver, filters, etc) using flavor extra specs. In some cases you 
would want to combine this capability with a mechanism that would ensure 
disjoint partitioning of the managed compute nodes between the drivers. 
This can be currently achieved by using host aggregates and 
AggregateInstanceExtraSpec filter of FilterScheduler. For example, if you 
want to apply driver_A on hosts in aggregate_X, and dirver_B on hosts in 
aggregate_Y, you would have flavor AX specifying driver_A and properties 
that would map to aggregate_X, and similarly for BY.

Hope this helps.


From:   sudheesh sk <sudh03 at yahoo.com>
To:     "openstack-dev at lists.openstack.org" 
<openstack-dev at lists.openstack.org>, 
Date:   13/08/2013 10:30 AM
Subject:        [openstack-dev] Can we use two nova schedulers at the same 


1) Can nova have more than one scheduler at a time? Standard Scheduler + 
one custom scheduler?

2) If its possible to add multiple schedulers - how we should configure 
it. lets say I have a scheduler called 'Scheduler' . So nova conf may look 
like below scheduler_manager = nova.scheduler.filters.SchedulerManager 
scheduler_driver = nova.scheduler.filter.Scheduler Then how can I add a 
second scheduler

3) If there are 2 schedulers - will both of these called when creating a 

I am asking these questions based on a response I got from ask openstack 

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