[openstack-dev] [nova] Rocky PTG summary - cells

Zhenyu Zheng zhengzhenyulixi at gmail.com
Thu Mar 15 12:34:12 UTC 2018

Thanks for the reply, both solution looks reasonable.

On Thu, Mar 15, 2018 at 10:29 AM, melanie witt <melwittt at gmail.com> wrote:

> On Thu, 15 Mar 2018 09:54:59 +0800, Zhenyu Zheng wrote:
>> Thanks for the recap, got one question for the "block creation":
>>     * An attempt to create an instance should be blocked if the project
>>     has instances in a "down" cell (the instance_mappings table has a
>>     "project_id" column) because we cannot count instances in "down"
>>     cells for the quota check.
>> Since users are not aware of any cell information, and the cells are
>> mostly randomly selected, there could be high possibility that
>> users(projects) instances are equally spreaded across cells. The proposed
>> behavior seems can
>> easily cause a lot of users couldn't create instances because one of the
>> cells is down, isn't it too rude?
> To be honest, I share your concern. I had planned to change quota checks
> to use placement instead of reading cell databases ASAP but hit a snag
> where we won't be able to count instances from placement because we can't
> determine the "type" of an allocation. Allocations can be instances, or
> network-related resources, or volume-related resources, etc. Adding the
> concept of an allocation "type" in placement has been a controversial
> discussion so far.
> BUT ... we also said we would add a column like "queued_for_delete" to the
> instance_mappings table. If we do that, we could count instances from the
> instance_mappings table in the API database and count cores/ram from
> placement and no longer rely on reading cell databases for quota checks.
> Although, there is one more wrinkle: instance_mappings has a project_id
> column but does not have a user_id column, so we wouldn't be able to get a
> count by project + user needed for the quota check against user quota. So,
> if people would not be opposed, we could also add a "user_id" column to
> instance_mappings to handle that case.
> I would prefer not to block instance creations because of "down" cells, so
> maybe there is some possibility to avoid it if we can get
> "queued_for_delete" and "user_id" columns added to the instance_mappings
> table.
> -melanie
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