Proposed new library oslo.limit

This is a proposal to create a new library dedicated to enabling moreconsistent quota and limit enforcement across OpenStack.

Proposed library mission

Enforcing quotas and limits across OpenStack has traditionally been a tough problem to solve. Determining enforcement requires quota knowledge from the service along with information about the project owning the resource. Up until the Queens release, quota calculation and enforcement has been left to the services to implement, forcing them to understand complexities of keystone project structure. During the Pike and Queens PTG, there were several productive discussions towards redesigning the current approach to quota enforcement.

Because keystone is the authority of project structure, it makes sense to allow keystone to hold the association between a resource limit and a project. This means services still need to calculate quota and usage, but the problem should be easier for services to implement since developers shouldn’t need to re-implement possible hierarchies of projects and their associated limits. Instead, we can offload some of that work to a common library for services to consume that handles enforcing quota calculation based on limits associated to projects in keystone. This proposal is to have a new library called oslo.limit that fills that need.

Consuming projects

The services consuming this work will be any service that currently implements a quota system, or plans to implement one. Since keystone already supports unified limits and association of limits to projects, the implementation for consuming projects is easier. instead of having to re-write that implementation, developers need to ensure quota calculation to passed to the oslo.limit library somewhere in the API’s validation layer. The pattern described here is very similar to the pattern currently used by services that leverage oslo.policy for authorization decisions.

Alternatives library

It looks like there was an existing library that attempted to solve some of these problems, called delimiter. It looks like delimiter could be used to talk to keystone about quota enforcement, where as the existing approach with oslo.limit would be to use keystone directly.

Proposed adoption model/plan

The unified limit API in keystone is currently marked as experimental, but the keystone team is actively collecting and addressing feedback that will result in stabilizing the API. Stabilization changes that effect the oslo.limit library will also be addressed before version 1.0.0 is released. From there, we can look to incorporate the library into various services that either have an existing quota implementation, or services that have a quota requirement but no implementation.

This should help us refine the interfaces between services and oslo.limit, while providing a facade to handle complexities of project hierarchies. This should enable adoption by simplifying the process and making it easier for quota to be implemented in a consistent way across services.

Reviewer activity

At first thought, it makes sense to model the reviewer structure after the oslo.policy library, where the core team consists of people not only interested in limits and quota, but also people familiar with the keystone implementation of the unified limits API.



Who is leading the proposal of the new library? Must have at least two individuals from the community committed to triaging and fixing bugs, and responding to test failures in a timely manner.

Primary authors:

Lance Bragstad ( lbragstad XiYuan Wang ( wxy

Other contributors:

<launchpad-id or None>

Work Items

  • Create a new library called oslo.limit

  • Create a core group for the project

  • Define the minimum we need to enforce quota calculations in oslo.limit

  • Propose an implementation that allows services to test out quota enforcement via unified limits


Rocky PTG etherpad for unified limits. This is where we discussed the interaction between services and keystone, ultimately agreeing on the inclusion of a library to handle quota enforcement.

Revision History


Release Name





This work is licensed under a Creative Commons Attribution 3.0 Unported License.