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

Sean McGinnis sean.mcginnis at gmx.com
Wed Mar 16 13:50:35 UTC 2016

On Wed, Mar 16, 2016 at 07:10:35AM -0400, Attila Fazekas wrote:
> NO : For any kind of extra quota service.
> In other places I saw other reasons for a quota service or similar,
>  the actual cost of this approach is higher than most people would think so NO.

I have to agree, there is a lot of hidden cost with making this its own
service, both on the development and end user side of things.

> Maybe Library,
> But I do not want to see for example the bad pattern used in nova to spread everywhere.
> The quota usage handling MUST happen in the same DB transaction as the 
> resource record (volume, server..) create/update/delete  .
> There is no need for.:
> - reservation-expirer services or periodic tasks ..
> - there is no need for quota usage correcter shell scripts or whatever
> - multiple commits
> We have a transaction capable DB, to help us,
> not using it would be lame.

I would much rather see a library that at least ensures our handling of
quotas is consistent across projects. We've implemented some things and
had some issues. Nova has implemented some things and had some issues.
Let's get this all in one place so we can all benefit from lessons
learned and work through these issues.

I'm sure there will still be problems. But I think it ends up being a
better user experience even if there are some quirks in the library. At
least they will be consistent quirks across all the projects instead of
needing to understand each project's own set of misbehavior.

> [2] http://lists.openstack.org/pipermail/openstack-dev/2015-April/061338.html
> ----- Original Message -----
> > From: "Nikhil Komawar" <nik.komawar at gmail.com>
> > To: "OpenStack Development Mailing List" <openstack-dev at lists.openstack.org>
> > Sent: Wednesday, March 16, 2016 7:25:26 AM
> > Subject: [openstack-dev] [cross-project] [all] Quotas -- service vs. library
> > 
> > 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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