[Openstack-operators] [nova] FYI, local conductor mode is deprecated, pending removal in N

Joshua Harlow harlowja at fastmail.com
Thu Nov 12 23:34:45 UTC 2015

Ok, so the following is starting to form:


Hopefully we can get to the bottom of this (especially for clouds that 
run a large amount of computes in a single cell/only one cell).

Andrew Laski wrote:
> On 11/12/15 at 10:53am, Clint Byrum wrote:
>> Excerpts from Joshua Harlow's message of 2015-11-12 10:35:21 -0800:
>>> Mike Dorman wrote:
>>> > We do have a backlog story to investigate this more deeply, we just
>>> have not had the time to do it yet. For us, it’s been easier/faster
>>> to add more hardware to conductor to get over the hump temporarily.
>>> >
>>> > We kind of have that work earmarked for after the Liberty upgrade,
>>> in hopes that maybe it’ll be fixed there.
>>> >
>>> > If anybody else has done even some trivial troubleshooting already,
>>> it’d be great to get that info as a starting point. I.e. which
>>> specific calls to conductor are causing the load, etc.
>>> >
>>> > Mike
>>> >
>>> +1 I think we in the #openstack-performance channel really need to
>>> investigate this, because it really worries me personally from hearing
>>> many many rumors about how the remote conductor falls over. Please join
>>> there and we can try to work through a plan to figure out what to do
>>> about this situation. It would be great if the nova people also joined
>>> there (because in the end, likely something in nova will need to be
>>> fixed/changed/something else to resolve what appears to be a problem for
>>> many operators).
>> Falling over is definitely a bad sign. ;)
>> The concept of pushing messages over a bus instead of just making local
>> calls shouldn't result in much extra load. Perhaps we just have too many
>> layers of unoptimized encapsulation. I have to wonder if something like
>> protobuf would help.
> Falling over is also a very broad description and doesn't let us know
> what the actual issue is.
>  From my experience the performance concern with conductor has been in
> not understanding the ratio of conductor nodes to computes that are
> necessary for our usage. Conductor doesn't add much extra load, but it
> concentrates it on a smaller number of services. If we ran one conductor
> per compute I suspect we would have no performance issues, but that's a
> lot of capacity to use for this.
> I am curious what conductor/compute ratios that others are trying to
> achieve, given equal hardware types for each, and what are the barriers
> to this happening?
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