[openstack-dev] [nova][scheduler][placement] Trying to understand the proposed direction

Jay Pipes jaypipes at gmail.com
Mon Jun 19 22:27:02 UTC 2017

On 06/19/2017 05:24 PM, Edward Leafe wrote:
> On Jun 19, 2017, at 1:34 PM, Jay Pipes <jaypipes at gmail.com 
> <mailto:jaypipes at gmail.com>> wrote:
>>> OK, thanks for clarifying that. When we discussed returning 1.5K per 
>>> compute host instead of a couple of hundred bytes, there was 
>>> discussion that paging would be necessary.
>> Not sure where you're getting the whole 1.5K per compute host thing from.
> It was from the straw man example. Replacing the $FOO_UUID with UUIDs, 
> and then stripping out all whitespace resulted in about 1500 bytes. Your 
> example, with whitespace included, is 1600 bytes.

It was the "per compute host" that I objected to.

>>> OK, that’s informative, too. Is there anything decided on how much 
>>> host info will be in the response from placement, and how much will 
>>> be in HostState? Or how the reporting of resources by the compute 
>>> nodes will have to change to feed this information to placement? Or 
>>> how the two sources of information will be combined so that the 
>>> filters and weighers can process it? Or is that still to be worked out?
>> I'm currtently working on a patch that integrates the REST API into 
>> the scheduler.
>> The merging of data will essentially start with the resource amounts 
>> that the host state objects contain (stuff like total_usable_ram etc) 
>> with the accurate data from the provider_summaries section.
> So in the near-term, we will be using provider_summaries to update the 
> corresponding HostState objects with those values. Is the long-term plan 
> to have most of the HostState information moved to placement?

Some things will move to placement sooner rather than later:

* Quantitative things that can be consumed
* Simple traits

Later rather than sooner:

* Distances between aggregates (affinity/anti-affinity)


* Filtering hosts based on how many instances use a particular image
* Filtering hosts based on something that is hypervisor-dependent
* Sorting hosts based on the number of instances in a particular state 
(e.g. how many instances are live-migrating or shelving at any given time)
* Weighing hosts based on the current temperature of a power supply in a 
* Sorting hosts based on the current weather conditions in Zimbabwe


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