[openstack-dev] [cross-project] [all] Quotas -- service vs. library

Boris Pavlovic boris at pavlovic.me
Wed Mar 16 07:34:16 UTC 2016


Thank you for rising this question.

IMHO quotas should be moved into separated services (this is right micro
services approach).

It will make a lot of things simpler:
1) this removes a lot of logic/code from projects
2) cross project atomic quotas reservation (will be possible)
   (e.g. if we would like to reserver all required quotas, before running
heat stack)
3) it will have better UX (you can change projects quotas from one place
and unified)
4) simpler migrations for the projects (we don't need to maintain db
migrations for each project)
    just imagine change in quotas lib that requires db migrations, we will
need to run amount of projects migrations.

Best regards,
Boris Pavlovic

On Tue, Mar 15, 2016 at 11:25 PM, Nikhil Komawar <nik.komawar at gmail.com>

> Hello everyone,
> tl;dr;
> I'm writing to request some feedback on whether the cross project Quotas
> work should move ahead as a service or a library or going to a far
> extent I'd ask should this even be in a common repository, would
> projects prefer to implement everything from scratch in-tree? Should we
> limit it to a guideline spec?
> But before I ask anymore, I want to specifically thank Doug Hellmann,
> Joshua Harlow, Davanum Srinivas, Sean Dague, Sean McGinnis and  Andrew
> Laski for the early feedback that has helped provide some good shape to
> the already discussions.
> Some more context on what the happenings:
> We've this in progress spec [1] up for providing context and platform
> for such discussions. I will rephrase it to say that we plan to
> introduce a new 'entity' in the Openstack realm that may be a library or
> a service. Both concepts have trade-offs and the WG wanted to get more
> ideas around such trade-offs from the larger community.
> Service:
> This would entail creating a new project and will introduce managing
> tables for quotas for all the projects that will use this service. For
> example if Nova, Glance, and Cinder decide to use it, this 'entity' will
> be responsible for handling the enforcement, management and DB upgrades
> of the quotas logic for all resources for all three projects. This means
> less pain for projects during the implementation and maintenance phase,
> holistic view of the cloud and almost a guarantee of best practices
> followed (no clutter or guessing around what different projects are
> doing). However, it results into a big dependency; all projects rely on
> this one service for right enforcement, avoiding races (if do not
> incline on implementing some of that in-tree) and DB
> migrations/upgrades. It will be at the core of the cloud and prone to
> attack vectors, bugs and margin of error.
> Library:
> A library could be thought of in two different ways:
> 1) Something that does not deal with backed DB models, provides a
> generic enforcement and management engine. To think ahead a little bit
> it may be a ABC or even a few standard implementation vectors that can
> be imported into a project space. The project will have it's own API for
> quotas and the drivers will enforce different types of logic; per se
> flat quota driver or hierarchical quota driver with custom/project
> specific logic in project tree. Project maintains it's own DB and
> upgrades thereof.
> 2) A library that has models for DB tables that the project can import
> from. Thus the individual projects will have a handy outline of what the
> tables should look like, implicitly considering the right table values,
> arguments, etc. Project has it's own API and implements drivers in-tree
> by importing this semi-defined structure. Project maintains it's own
> upgrades but will be somewhat influenced by the common repo.
> Library would keep things simple for the common repository and sourcing
> of code can be done asynchronously as per project plans and priorities
> without having a strong dependency. On the other hand, there is a
> likelihood of re-implementing similar patterns in different projects
> with individual projects taking responsibility to keep things up to
> date. Attack vectors, bugs and margin of error are project responsibilities
> Third option is to avoid all of this and simply give guidelines, best
> practices, right packages to each projects to implement quotas in-house.
> Somewhat undesirable at this point, I'd say. But we're all ears!
> Thank you for reading and I anticipate more feedback.
> [1] https://review.openstack.org/#/c/284454/
> --
> Thanks,
> Nikhil
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