On 11/06/13 at 09:47am, Sylvain Bauza wrote:

During the Design session 
https://etherpad.openstack.org/p/NovaIcehouse-Instance-Group-API we discussed 
the fact that this is not the role of Nova for doing atomic reservations in 
order to ensure the user needs will be met.

We discussed that it's not Nova's role to do atomic reservations of groups of resources. But two phase commit came up a number of times for single instance scheduling/reservations which would allow reservations of groups to occur with some outside coordination.

I raised the point (and sorry for my bad accent, was stressy) that we're 
already trying to provide a reservation system for Openstack, called Climate (a 
Stackforge project).
I would really like to discuss with you all, Nova community, about the 
reservation system and ensure that we, at Climate, are on the good path.

I think Climate has some interesting potential around capacity planning and would like to see it integrate well with Nova. But my understanding of both proposals makes me think that the reservation system that Climate wants to provide isn't the best solution for the Instance Group work. Instance Groups, or the longer term idea of Resource Groups should be workable with two phase commit since it's concerned about what can be placed at that moment. Climate also considers future placements which is very cool but leads(potentially) to different design considerations and trade-offs.

One thing that isn't clear to me from the etherpad (https://etherpad.openstack.org/p/NovaIcehouse-ClimateInteractions) and the discussion is what API behaviour in Nova would be ideal for Climate? You've listed questions about pclouds and host aggregates and other things that Nova provides, but those seem like implementation details to me. What kinds of actions could Nova provide that would allow Climate to function well?

Climate is planning to reserve both virtual instances and physical hosts, but 
for the discussion we had, only physical hosts usecase is relevant.

We had an unconference session today at 2pm, I can share you the slides :


(please focus on slides 11-14, they're talking on the design for host 

All the code is located on Stackforge, but please note the most important part 
of physical host reservations is still under review there :

(We're missing reviewers, by the way !)

I'm open to discuss and waiting your thoughts,

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