# Unified Limits API¶

Detailed specification for the work necessary to associate resources limits to projects.

bp unified-limits

## Problem Description¶

Today, resource quotas are maintained outside Keystone in each project, such as Nova, Cinder or others. This leads to a problem where there is no strong relationship between projects and their resources. For example, when a user sets a quota in Nova like “project A can create 10 virtual machines”, but if project A doesn’t exist in Keystone, Nova will still create the quota. If the project A is deleted in Keystone, Nova doesn’t know it and will still leave the quota there. This problem is only exacerbated when dealing with project hierarchies.

More information on this problem and the overall approach can be found in a separate high-level specification.

## Proposed Change¶

An interface to create, read, update, delete limit definitions. It includes two kinds of Limits: Registered Limits and Project Limits. Registered Limits are the defaults limits. You can’t set a project limit on something that’s not a registered limit. Project Limits are the limits that override registered limits for each project.

Note

This spec doesn’t talk about the usage check of limits. It is up to the consuming services to enforce usage.

### Registered Limits¶

The following API calls are specific to the management of Registered Limits.

### Create Registered Limits¶

Limits are registered with the Registered Limits endpoint. Because limits definitions will often be created in bulk, this supports sending a number of limit definitions at once. This is an admin only action.

Request: POST /registered-limits

Request Parameters

• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in. If the region_id is specified, it should be keep the same with the consuming service’s. If not, Keystone will leave it empty like endpoint does.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Request Body

{
"limits": [
{
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"default_limit": 10
},
{
"service_id": "77232e5107074dfe801657000348e8c9",
"resource_name": "ram_mb",
"default_limit": 20480
},
]
}


Response

A full list of all registered limits.

Response Parameters

• id - The unique uuid for each registered limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Response Code

• 200 - OK
• 400 - Bad Request - if dependent resources do not exist
• 403 - Forbidden - if the user is not authorized to create a registered limit
• 409 - Limits that already exist

Response Body:

{
"limits": [
{
"id": "0681e10c01c044d78ef8e5cb592c6446",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"default_limit": 10
},
{
"id": "1dc633fe5acd4182b63f68c9cc8e768a",
"service_id": "77232e5107074dfe801657000348e8c9",
"resource_name": "ram_mb",
"default_limit": 20480
},
{
"id": "5c4182eb45304cb3ac89030b19ab5a81",
"service_id": "ae22fb0dfbd34464bf67e758977f4839",
"region_id": "regionOne",
"resource_name": "storage_gb",
"default_limit": 20
},
]
}


### Update Registered Limits¶

Update is done similar to a POST however just the limits that you wish to override are included. If the service_id, region_id, or resource_name doesn’t already exist, an error is thrown.

Request: PUT /registered-limits

Request Parameters

• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region_id that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Request Body

{
"limits":[
{
"id": "1dc633fe5acd4182b63f68c9cc8e768a",
"service_id": "77232e5107074dfe801657000348e8c9",
"resource_name": "ram_mb",
"default_limit": 10240
}
]
}


Response:

A full list of all limits. That allows for double checking one’s work.

Response Code:

• 200 - OK
• 400 - Bad Request - if dependent resources do not exist
• 403 - Forbidden - if the user is not authorized to update a registered limit

Response Parameters

• id - The unique uuid for each registered limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Response Body:

{
"limits": [
{
"id": "0681e10c01c044d78ef8e5cb592c6446",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"default_limit": 10
},
{
"id": "1dc633fe5acd4182b63f68c9cc8e768a",
"service_id": "77232e5107074dfe801657000348e8c9",
"resource_name": "ram_mb",
"default_limit": 10240
},
{
"id": "5c4182eb45304cb3ac89030b19ab5a81",
"service_id": "ae22fb0dfbd34464bf67e758977f4839",
"region_id": "regionOne",
"resource_name": "storage_gb",
"default_limit": 20
},
]
}


### List all Registered Limits¶

Registered limits can be read by anyone with a valid token.

Request: GET /registered-limits

Request filter:

Registered limits will also support filters to make it easier to see just a subset. service_id, region_id, and resource_name will all be valid search parameters.

Response:

A full list of all registered limits.

Response Code:

• 200 - OK
• 403 - Forbidden - if the user is not authorized to list registered limits

Response Parameters

• id - The unique uuid for each registered limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Response Body:

{
"limits": [
{
"id": "0681e10c01c044d78ef8e5cb592c6446",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"default_limit": 10
},
{
"id": "1dc633fe5acd4182b63f68c9cc8e768a",
"service_id": "77232e5107074dfe801657000348e8c9",
"resource_name": "ram_mb",
"default_limit": 20480
},
{
"id": "5c4182eb45304cb3ac89030b19ab5a81",
"service_id": "ae22fb0dfbd34464bf67e758977f4839",
"region_id": "regionOne",
"resource_name": "storage_gb",
"default_limit": 20
},
]
}


### Show a Registered Limits¶

Registered limits can be read by anyone with a valid token.

Request: GET /registered-limits/{registered-limits-id}

Request Parameters

• registered-limits-id - The id for the specified registered limit.

Response:

The specified registered limit.

Response Code:

• 200 - OK
• 403 - Forbidden - if the user is not authorized to retrieve a registered limit
• 404 - Not Found - if the requested registered limit does not exist

Response Parameters

• id - The unique uuid for each registered limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• default_limit - The default limit for all projects to assume for that resource.

Response Body:

{
"id": "0681e10c01c044d78ef8e5cb592c6446",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"default_limit": 10
}


### Delete a Registered Limit¶

Request: DELETE /registered-limits/{registered-limits-id}

Request Parameters

• registered-limits-id - The id for the specified registered limit.

Response:

No content.

Response Code:

• 204 - No Content
• 403 - Forbidden - if the user is not authorized to delete a registered limit
• 404 - Not Found - if the requested registered limit does not exist

### Project Limits¶

The following API calls are specific to the management of Project Limits. They are project administrator only (system admin as well) APIs.

Note

The initial implementation will only support a “flat” hierarchical model. In this model, the limits associated to a project will be validated as a flat structure. This means limits won’t be enforced or validated according to the parents, childred, or peers of the project. All limits will be independent of those relationships. This is referred to as a “flat” enforcement model. Future work will elaborate on more complex enforcement models that understand project hierarchies.

### Create Project Limits¶

Overriding Registered Limits with Project Limits.

Request: POST /limits

Request Parameters

• project_id (optional) - The project which assume the limit. If omit, Keystone will get the project_id from token (context).
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in. It should use same region_id of the registered limit which will be overridden.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• resource_limit - The override limit for the project to assume for that resource.

Request Body

{
"limits":[
{
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "ram_mb",
"resource_limit": 10240,
},
{
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"resource_limit": 10,
},
]
}


Response:

We return the entire limits structure, including defaults without overrides.

Response Code:

• 200 - OK
• 400 - Bad Request - if dependent resources do not exist
• 403 - Forbidden - if the user is not authorized to change the limit for that project
• 409 - Limits that already exist

Response Parameters

• id - The id for the specified limit.
• project_id - The project which assume the limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• resource_limit - The override limit for the project to assume for that resource.

Response Body:

{
"limits":[
{
"id": "aaab50e9c36f4a84bab98dfc117c9836",
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "ram_mb",
"resource_limit": 10240,
},
{
"id": "e08fcb2756be48e387e821bd79e29538",
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"resource_limit": 10,
},
]
}


### Update Project Limits¶

Update Project Limits. Once the project limit is created, The only property that can be changed is resource_limit.

Request: PUT /limits

Request Parameters:

• resource_limit - The override limit for the project to assume for that resource.

Request Body:

{
"limits":[
{
"id": "aaab50e9c36f4a84bab98dfc117c9836",
"resource_limit": 5120,
},
{
"id": "e08fcb2756be48e387e821bd79e29538",
"resource_limit": 5,
},
]
}


Response:

We return the entire limits structure, including defaults without overrides.

Response Code:

• 200 - OK
• 400 - Bad Request - if registered limit matching the resource name or the project limit with the given ID do not exist
• 403 - Forbidden - if the user is not authorized to change the limit for that project

Response Parameters

• id - The id for the specified limit.
• project_id - The project which assume the limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• resource_limit - The override limit for the project to assume for that resource.

Response Body:

{
"limits":[
{
"id": "aaab50e9c36f4a84bab98dfc117c9836",
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "ram_mb",
"resource_limit": 5120,
},
{
"id": "e08fcb2756be48e387e821bd79e29538",
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"resource_limit": 5,
},
]
}


### List Project Limits¶

Request: GET /limits

Request filter:

• project_id - Only used for cloud admin to filter limits with the specified project_id. Project admin can only list the limits for their own projects.

limits will also support filters to make it easier to see just a subset. service_id, region_id, and resource_name will all be valid search parameters.

Response:

A list of all limits in a project.

Response Code:

• 200 - OK
• 403 - Forbidden - if the user is not authorized to list limits for that project

Response Parameters

• id - The id for the specified limit.
• project_id - The project which assume the limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• resource_limit - The override limit for the project to assume for that resource.

Response Body:

{
"limits":[
{
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "ram_mb",
"resource_limit": 10240,
},
{
"project_id": "95541dbfaa054cab86510e0d0a87896a",
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "cores",
"resource_limit": 10,
},
]
}


### Show a Project Limit¶

Request: GET /limits/{limit-id}

Request Parameters:

• limit-id - The id for the specified limit.

Response:

The detail of the specified limit.

Response Code:

• 200 - OK
• 403 - Forbidden - if the user is not authorized to retrieve that project limit
• 404 - Not Found - if the requested project limit does not exist

Response Parameters

• id - The id for the specified limit.
• project_id - The project which assume the limit.
• service_id - The service that is responsible for the resource, which should match a service in the service catalog.
• region_id (optional) - The region that the service is hosted in.
• resource_name - The name of the resource, which should be unique compared to other resource names for the same service and region.
• resource_limit - The override limit for the project to assume for that resource.

Response Body:

{
"project_id": "95541dbfaa054cab86510e0d0a87896a"
"service_id": "77232e5107074dfe801657000348e8c9",
"region_id": "regionOne",
"resource_name": "ram_mb",
"resource_limit": 10240,
}


### Delete a Project Limit¶

Request: DELETE /limits/{limit-id}

Request Parameters

• limit-id - The id for the specified limit.

Response:

No content

Response Code:

• 204 - No Content
• 403 - Forbidden - if the user is not authorized to delete a limit for that project
• 404 - Not Found - if the requested project limit does not exist

### Flat Hierarchy Enforcement¶

Keystone supports hierarchical multi-tenancy, where projects can be grouped into tree structures and have parents, siblings, and children. It’s possible to think of various ways where a project limit interacts differently depending on the limits of other projects in the tree. The initial implementation of project limits documented in this specification is going to account for a flat structure. This means the limit information and validation does not account for other projects in the hierarchy. Each project has it’s own limit.

Assume project P is a child of project F, which is a child of project A. A default is set on a limit, all projects get that effective default.

Assuming we have a default limit of 10

And then we UPDATE LIMIT on A to 20

Or we can UPDATE LIMIT on P to 30

This is allowed with flat enforcement because the hierarchy is not taken into consideration during limit validation. In the future, we will introduce a model that has the ability to validate limits with respect to project hierarchies. It is important to note that switching between enforcement models will require extremely careful planning and possibly lead to API changes depending on the request being made and the new enforcement model. Deployments need to be aware of this, understand the ramifications of switching enforcement models, and the impacts it can have on existing limits.

Keystone will also expose a GET /limits-model endpoint that is responsible for returning the enforcement model selected by the deployment. This is key to allowing discoverable limit models and perserving interoperability between OpenStack deployments with different enforcement models.

### Alternatives¶

One alternative that’s already been taken by at least one project is to attempt to implement hierarchical quotas in the service itself. Since understanding the hierarchy can be confusing, not duplicating that logic is what lead us to this approach, which keeps the limit closely associated to the hierarchy.

Another alternative is that we can add limits inside projects. The API will be like /projects/{project_id}/limits/{limit_id}. These APIs has ways of showing a project hierarchy already. In this way, we can reuse it easily.

### Security Impact¶

The enforcement and validation of limits targeted in this work is specific to flat hierarchies. This means that limits are associated to project independently, regardless of parent, children, or peer projects. For example, assume project alpha is a parent of projects bravo and charlie. A flat hierarchy would allow bravo to have a limit of 10 instances while charlie and alpha may only have a limit of 5 instances. From the perspective of a project hierarchy, this may feel unintuitive. This is the first enforcement model implementation and once we build knowledge and collect usage feedback, there will be an effort to develop more sophisticated enforcement models that account for project hierarchies.

Registered limits should be considered public information and discoverable. Project limits should be available to members of the project. A user with a role on project alpha should be able to list limits for the project, but not for bravo or charlie. This case will become more complicated in the future when we start developing enforcement models that account for hierarchies.

When more complicated models are introduced, we will need a way to provide sufficient information to the user to allow them to understand why a limit update has failed or why a resource request brings them over quota without divulging too much information about related projects. This will not need to be addressed with this initial “flat” implementation.

Registered Limits and Project Limits should be subject to the same notifications as other resources in keystone.

### Other End User Impact¶

None. End users will be able to query keystone for limit information. This improves usability because they can see what the limit is and gather more information when requesting help from an administrator.

### Performance Impact¶

The internal performance impact of the initial flat hierarchy design should be negligible. This will likely become more complicated once development for hierarchical enforcement models starts (e.g. calculating limits of a project with respect to its parent(s), children, and peers). Keystone will then have to compute more complicated limit structure.

Other services will be required to make additional calls to keystone to retrieve limit information in order to do quota enforcement. This will add some overhead to the overall performance of the API call.

It is also worth noting that both Registered Limits and Project Limits are not expected to change frequently. This means the data is safe to cache for some period of time. Caching will be implemented internally to keystone, similar to how keystone caches responses for other resources. But, caching can also be done client-side to avoid making frequent calls to keystone for relatively static limit information.

### Other Deployer Impact¶

Deployments looking to have Registered Limits and Project Limits in keystone will have to set that up at installation time. This creates an extra step for operators, similar to how they register services in the service catalog.

### Developer Impact¶

Developers from other projects will likely have the following questions:

• What the difference between a Registered Limits and Project Limit?
• What information is relayed in the limit?
• How do I enforce usage based on the information about a limit?
• Is there a library to do this for me?

There are a lot of things we’ll have to make sure we communicate to developers looking to implement hierarchical quotas. Keystone’s really just the information point here. We need to be available on the other side to help them consume that information.

These questions, among others, will likely have to be answered in developer documentation within keystone.

## Implementation¶

### Assignee(s)¶

Primary assignee:

Other contributors:

### Work Items¶

1. Implement unified limits, add the new APIs mentioned above to Keystone.
2. Implement client support for unified limits.
3. Document limit models, Document unified limits, add related developer and user DOC.

The epic tracking this work can be found in keystone’s Queens roadmap.

Note

Make sure the APIs are generic enough so that we can support more quota model in the future.

None

## Documentation Impact¶

The usage of the new limit APIs should be addressed.

## References¶

High-level overview of limits.