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

Zhenyu Zheng zhengzhenyulixi at gmail.com
Thu Mar 15 01:54:59 UTC 2018

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?


Kevin Zheng

On Thu, Mar 15, 2018 at 2:26 AM, Chris Dent <cdent+os at anticdent.org> wrote:

> On Wed, 14 Mar 2018, melanie witt wrote:
> I’ve created a summary etherpad [0] for the nova cells session from the
>> PTG and included a plain text export of it on this email.
> Nice summary. Apparently I wasn't there or paying attention when
> something was decided:
>  * An attempt to delete an instance in a "down" cell should result in a
>> 500 or 503 error.
> Depending on how we look at it, this doesn't really align with what
> 500 or 503 are supposed to be used. They are supposed to indicate
> that the web server is broken in some fashion: 500 being an
> unexpected and uncaught exception in the web server, 503 that the
> web server is either overloaded or down for maintenance.
> So, you could argue that 409 is the right thing here (as seems to
> always happen when we discuss these things). You send a DELETE to
> kill the instance, but the current state of the instance is "on a
> cell that can't be reached" which is in "conflict" with the state
> required to do a DELETE.
> If a 5xx is really necessary, for whatever reason, then 503 is a
> better choice than 500 because it at least signals that the broken
> thing is sort of "over there somewhere" rather than the web server
> having an error (which is what 500 is supposed to mean).
> --
> Chris Dent                       ٩◔̯◔۶           https://anticdent.org/
> freenode: cdent                                         tw: @anticdent
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