On Fri, 2019-06-07 at 07:38 +0000, Balázs Gibizer wrote:
On Fri, Jun 7, 2019 at 1:31 AM, Sean Mooney <smooney@redhat.com> wrote:
On Thu, 2019-06-06 at 16:52 -0500, Eric Fried wrote:
Let me TL;DR this:
The forbidden aggregates filter spec [1] says when we put trait metadata onto a host aggregate, we should add the same trait to the compute node RPs for all the hosts in that aggregate, so that the feature actually works when we use it.
But we never talked about what to do when we *remove* a trait from such an aggregate, or trash an aggregate with traits, or remove a host from such an aggregate.
Here are the alternatives, as Vrushali laid them out (letters added by me):
(a) Leave all traits alone. If they need to be removed, it would have to be manually via a separate step.
(b) Support a new option so the caller can dictate whether the operation should remove the traits. (This is all-or-none.)
(c) Define a "namespace" - a trait substring - and remove only traits in that namespace.
I'm going to -1 (b). It's too big a hammer, at too big a cost (including API changes).
If Iʼm not wrong, for last two approaches, we would need to change RestFul APIs.
No, (c) does not. By "define a namespace" I mean we would establish a naming convention for traits to be used with this feature. For example:
CUSTOM_AGGREGATE_ISOLATION_WINDOWS_LICENSE
i personaly dislike c as it means we cannot use any standard traits in host aggrates.
there is also an option d. when you remove a trait form a host aggregate for each host in the aggregate check if that traits exists on another aggregate the host is a member of and remove it if not found on another aggregate.
Besides possible performance impacts, I think this would be the logical behavior from nova to do.
option d is worstcase aproxmatly O(NlogN) but is technicall between O(n) and O(NM) where N is the number of instance and M is the maxium number of aggrates a host is a memeber of. so it grows non linearly but the plroblem is not quadratic and is much closer to O(N) or O(NlogN) then it is to O(N^2) so long if we are smart about how we look up the data form the db its probably ok. we are basically asking for all the host in this aggrate, give me the hosts that dont have another aggrate with the trait i am about to remove form this aggragte. those host are the set of host we need to update in placemnt and sql is good at anserwing that type of question. if we do this in python it will make me sad.
cheers, gibi