All VMs fail when --max exceeds available resources

melanie witt melwittt at
Thu Nov 21 00:04:59 UTC 2019

On 11/20/19 15:16, Albert Braden wrote:
> The expected result (that I was seeing last week) is that, if my cluster has capacity for 4 VMs and I use --max 5, 4 will go active and 1 will go to error. This week all 5 are going to error. I can still build 4 VMs of that flavor, one at a time, or use --max 4, but if I use --max 5, then all 5 will fail. If I use smaller VMs, the --max numbers get bigger but I still see the same symptom.

The behavior you're describing is an old issue described here:

I don't understand how it's possible that you saw the 4 active 1 in 
error behavior last week. The behavior has been "error all" since 2015, 
at least. Unless there's some kind of race condition bug happening, 
maybe. Did you consistently see it fulfill less than --max last week or 
was it just once?

Changing the behavior would be an API change so it would need a spec and 
new microversion, I think. It's been an undesirable behavior for a long 
time but it seemingly hasn't been enough of a pain point for someone to 
sign up and do the work.


> The --max thing is pretty useful and we use it a lot; it allows us to use up the cluster without knowing exactly how much space we have.
> -----Original Message-----
> From: Matt Riedemann <mriedemos at>
> Sent: Wednesday, November 20, 2019 2:00 PM
> To: openstack-discuss at
> Subject: Re: All VMs fail when --max exceeds available resources
> On 11/20/2019 3:21 PM, Albert Braden wrote:
>> I think the document is saying that we need to set them in nova.conf on each HV. I tried that and it seems to fix the allocation failure:
>> root at us01odc-dev1-ctrl1:~# os resource provider inventory list f20fa03d-18f4-486b-9b40-ceaaf52dabf8
>> +----------------+------------------+----------+----------+-----------+----------+--------+
>> | resource_class | allocation_ratio | max_unit | reserved | step_size | min_unit |  total |
>> +----------------+------------------+----------+----------+-----------+----------+--------+
>> | VCPU           |              1.0 |       16 |        2 |         1 |        1 |     16 |
>> | MEMORY_MB      |              1.0 |   128888 |     8192 |         1 |        1 | 128888 |
>> | DISK_GB        |              1.0 |     1208 |      246 |         1 |        1 |   1208 |
>> +----------------+------------------+----------+----------+-----------+----------+--------+
> Yup, the config on the controller doesn't apply to the computes or
> placement because the computes are what report the inventory to
> placement so you have to configure the allocation ratios there, or
> starting in stein via (resource provider) aggregate.
>> This fixed the "allocation ratio" issue but I still see the --max issue. What could be causing that?
> That's something else yeah? I didn't quite dig into that email and the
> allocation ratio thing popped up to me since it's been a long standing
> known painful issue/behavior change since Ocata.
> One question though, I read your original email as essentially "(1) I
> did x and got some failures, then (2) I changed something and now
> everything fails", but are you running from a clean environment in both
> test scenarios because if you have VMs on the computes when you're doing
> (2) then that's going to change the scheduling results in (2), i.e. the
> computes will have less capacity since there are resources allocated on
> them in placement.

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