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Thank’s a lot ! 
I changed the settings and indeed, it seems to work. This distribution of instances is really interesting. I learn a lot.
Question: is it possible to view the calculated weight when choosing a server?
Otherwise, thanks again, really

Franck

> Le 16 févr. 2022 à 03:35, Tony Liu <tonyliu0592 at hotmail.com> a écrit :
> 
> Build failure could be caused by different things, networking, storage, hypervisor, etc.
> For example, failure caused by Neutron service, that doesn't mean this hypervisor is
> not healthy, but because of that weigher, even Neutron service is recovered, this
> hypervisor is still excluded from holding instance. This doesn't make sense.
> I wouldn't enable this weigher until it's smart enough to know the failure is caused
> by hypervisor itself, but not anywhere else.
> 
> Tony
> ________________________________________
> From: Laurent Dumont <laurentfdumont at gmail.com>
> Sent: February 15, 2022 05:00 PM
> To: Tony Liu
> Cc: Franck VEDEL; openstack-discuss
> Subject: Re: [kolla-ansible][nova]Problem with distribution of instance on servers
> 
> In a healthy setup, should build_failure_weight_multiplier be triggered?
> 
> From the doc, tweaking this might mean you try to schedule and built instances on computes that are not healthy.
> 
> On Tue, Feb 15, 2022 at 6:38 PM Tony Liu <tonyliu0592 at hotmail.com<mailto:tonyliu0592 at hotmail.com>> wrote:
> Enable debug logging on nova-scheduler, you will see how the winner is picked.
> I had the same issue before, caused by the build-failure weigher enabled by default.
> setting build_failure_weight_multiplier to 0 resolved issue for me. Instances are
> balanced by weighers (compute and memory) as expected.
> shuffle_best_same_weighed_hosts and host_subset_size are not necessary, unless
> it's required by certain cases.
> 
> Tony
> ________________________________________
> From: Laurent Dumont <laurentfdumont at gmail.com<mailto:laurentfdumont at gmail.com>>
> Sent: February 15, 2022 12:54 PM
> To: Franck VEDEL
> Cc: openstack-discuss
> Subject: Re: [kolla-ansible][nova]Problem with distribution of instance on servers
> 
> There are two settings we've tweaked in the past in Nova.
> 
> shuffle_best_same_weighed_hosts  --> Allow more spreading in the case of computes with the exact same specs/weights.
> host_subset_size --> Helps with concurrent requests to get different hosts
> 
> Before that, we saw the same behavior with Openstack stacking VM on single computes. It still respects anti-affinity, but I don't see a good reason to not spread as a default. Changing these two was enough to allow our spread to get a little better.
> 
> On Tue, Feb 15, 2022 at 11:19 AM Franck VEDEL <franck.vedel at univ-grenoble-alpes.fr<mailto:franck.vedel at univ-grenoble-alpes.fr><mailto:franck.vedel at univ-grenoble-alpes.fr<mailto:franck.vedel at univ-grenoble-alpes.fr>>> wrote:
> Hello,
> I seem to have a problem that I hadn't seen.
> I have 3 servers for my openstack, built with Kolla-ansible, I'm in Victoria version.
> I had simply put the 3 servers in the [compute] part of the multinode file, at first it worked, but for some time all the VMs are placed on server 1.
> 
> The 3 servers are operational, identical. here are 3 screenshots to show it. (on the images, the instances on servers 2 and 3 are present because it worked correctly, but no more instances are created on these servers now)
> [cid:17eff2778356f37a4481]
> [cid:17eff277835e47aa83c2]
> [cid:17eff2778356f53d34a3]
> 
> 
> I tried to understand how the instances are distributed on the servers, but in my case, I don't understand why none are assigned to the 2nd and 3rd server.
> How to find the problem? It should be nova-scheduler . Do you have to do anything special? Go see if a parameter has a bad value?
> 
> 
> Thanks in advance if you can help me.
> 
> Franck VEDEL
> 

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