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

Tim Bell Tim.Bell at cern.ch
Wed Mar 16 07:15:42 UTC 2016

On 16/03/16 07:25, "Nikhil Komawar" <nik.komawar at gmail.com> wrote:

>Hello everyone,
>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.
>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.

This has been proposed a number of times in the past with projects such as Boson
(https://wiki.openstack.org/wiki/Boson) and an extended discussion at one of the
summits (I think it was San Diego).

Then, there were major reservations from the PTLs at the impacts in terms of
latency, ability to reconcile and loss of control (transactions are difficult, transactions
across services more so).

>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!

I would favor a library, at least initially. If we cannot agree on a library, it
is unlikely that we can get a service adopted (even if it is desirable).

A library (along the lines of 1 or 2 above) would allow consistent implementation
of nested quotas and user quotas. Nested quotas is currently only implemented
in Cinder and user quota implementations vary between projects which is 

Now that we have Oslo (there was no similar structure when it was first discussed),
we have the possibility to implement these concepts in a consistent way across
OpenStack and give a better user experience as a result.


>Thank you for reading and I anticipate more feedback.
>[1] https://review.openstack.org/#/c/284454/
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