On Tue, 2024-07-23 at 14:22 +0000, dwest576@me.com wrote:

The filter excludes devices, whereas the scheduler creates a score and decides where to put it.   Filter before scheduler.

that is incorrect. the schduler refers to two differnting things the nova-scheduler binsary. and the schduler class exectued by the binary. in the past the nova-schdueler could be configured with a number of implemetionts like the caching schduler and the filter scheduler. the way schdulign works in nova is docuemated here https://docs.openstack.org/nova/latest/admin/scheduling.html wifrst wehn we make an RPC call to the schduler process (select_destiatnions https://github.com/openstack/nova/blob/master/nova/scheduler/manager.py#L148) the scdhuler computes a request to the placment services's allocation candaties api which returns a set of possibel allocation (on specific hosts) where the instance could fit. the host manager https://github.com/openstack/nova/blob/master/nova/scheduler/host_manager.py in the schduler then prepares a set of host_state objects fro each host that has an allcoation candiate and it invokes the _get_sorted_hosts https://github.com/openstack/nova/blob/master/nova/scheduler/manager.py#L700 internally tahat first invokes get_filtered_hosts which uses the filters to elimiate any host that do not pass the filter. after that the filter schduler weiehse the remainign host buy applying all enbaled weighers to rank each of the hosts. we then take the resultant list and return N hosts and there allcoation candiates as the result of the rpc call. where n is set by [filter_schduler]host_subset_size the addtional hosts are sued as alternite host if the first selected host should not be able to boot the vm for any reason

Get Outlook for iOS<https://aka.ms/o0ukef> ________________________________ From: Gk Gk <ygk.kmr@gmail.com> Sent: Tuesday, July 23, 2024 2:33:43 AM To: openstack-discuss <openstack-discuss@lists.openstack.org> Subject: Scheduler and filters

Hi,

Can anyone tell me the difference between the schedulers and filters in nova. As per what I grasped, it seems we have the same type of weighers like schedulers. Then what's the difference  ? Please explain..

Thanks Y.G