Resource-pool projects

This document describes the current state of the quota and projects system, and proposes a new design for projects that would function as resource pools. It sketches implementation details and migration concerns.

Current state and shortcomings

Each Synnefo user is granted quota for several resources. These quota originate from two different sources: the system and projects. By default a user holds so-called base quota granted by the system upon activation; base quota can be customized per user. When a user joins a project, resources offered by the project add up to the existing quota, increasing the total amount of resources one can reserve.

This design fails to associate an actual (reserved) resource (e.g. VM) with a particular project. There is no way to tell which project a resource originates from and is thus not possible to employ any targeted policy when a user leaves a project, such as reclaiming the granted resource. It is also not possible to employ more advanced access control on resources, such as sharing VMs among members of a project.

Proposed changes

We will alter project semantics so that a project is viewed as a pool of finite resources. Each project member can reserve a portion of these resources up to a specified limit. Each actual resource (e.g. VM) is associated with a particular project. Admission of a user to a project will no more result in increasing the user’s existing overall quota, but in defining new project-specific quota for the user.

A project defines a pair of limits for each resource that it grants (e.g. cyclades.vm): project-level limit and member-level limit; The former is the total amount of a resource that this project can grant; the latter is the maximum amount that an individual user (project member) can reserve and cannot exceed the former. A limit on the number of members allowed is still enforced.

Projects will be the sole source of resources. Current base quota offered to users by the system will be expressed in terms of special-purpose base projects.

Implementation details

Project-related quota holdings

The Quotaholder is responsible to record all resource allocations and deallocations, and enforce the limits. It keeps counters of the following structure:

• resource: the resource name (e.g. cyclades.vm)
• holder: the entity holding the resource (user or project)
• source: the origin of the resource; a user-holder reserves from a project, a project is a top-level entity and reserves from nowhere (None)
• limit: maximum allowed allocation (an integer)
• usage: current allocation (an integer)

[Due to the transactional nature of the mechanism, there are actually two usage fields (usage_min and usage_max). Details are beyond the scope of this document.]

Creation of a new project triggers the creation of counters like:

resource      holder              source   limit   usage
------------|-------------------|--------|-------|------
cyclades.vm   project:projectID   None     50      0

When a user is admitted in a project, counters are created like:

resource      holder          source              limit   usage
------------|---------------|-------------------|-------|------
cyclades.vm   user:userUUID   project:ProjectID   5       0

Note that the two types of holders (and sources) are made distinguishable with a prefix: user: or project:.

When a user leaves a project, the latter limit is set to zero. This results in the project-specific user quota being over limit and prohibits any further allocation that would increase this counter. When a project is deactivated, the limit of both types of counters is set to zero. No user can perform any allocation related to this project. However, the holdings cannot be deleted as long as a non-zero usage is recorded. Deallocation is always allowed as long as usage does not fall below zero. Counters with zero usage and limit could by garbage collected by Astakos, if needed.

Base projects

For reasons of uniformity, we replace the base quota mechanism with projects. In a similar vein to OpenStack tenants, we define new user-specific base projects to account for the base quota for each user. These projects should be clearly associated with a single user, restrict join/leave actions and specify the quota granted by the system. When a new user is created, their base project will be automatically created and linked back to the user. User activation will trigger project activation, granting the default resource quota. Base projects will have no owner, marked thusly as `system’ projects. The administrator can, following the usual project logic, alter quota by modifying the project. Users cannot apply for modification of their base projects.

Projects will, from now on, be identified by a UUID. Base projects will receive the same UUID as the user itself. ProjectID, which appears above in the Quotaholder entries, refers to the project UUID.

Base quota will be expressed both in terms of a project-level and a member-level limit. This will result in two operationally equivalent Quotaholder counters, as in the following example. In the future, we could admit third-party users to a user’s base project; in that case, those counters would differ.

resource      holder         source         limit   usage
------------|--------------|--------------|-------|------
cyclades.vm   project:uuid   None           5       1
cyclades.vm   user:uuid      project:uuid   5       1

System default quota

Each resource registered in the system is assigned a default quota limit. A newly-activated user is given these limits as their base quota. This is till now done by copying the default limits as user’s entries in AstakosUserQuota. Default limits will from now on be copied into the base project’s resource definitions.

Conventional projects are created through a project application, which may not specify limits for all resources registered in the system. In fact, it may even be impossible to specify a resource, if it is set api_visible=False. We have to somehow specify these limits. Defaulting to zero is not appropriate: if we don’t want to control a resource, we would like it set to infinite. We thus need an extra skeleton, like the one specifying the default base quota, in order to fill in missing limits for conventional projects. It will be controled by a new option --project-default of command resource-modify.

Private projects

Since the introduction of base projects will explode the number of total projects, we will need to control their visibility. We add a new flag private in project definitions. A private project can only be accessed by its owner and members and not be advertised in the UI. Base projects are marked as private.

Allocation of a new resource

When a service allocates a new resource, it should associate it both with a user and a project. The commission issued to the Quotaholder should attempt to update all related counters. For example, it should include the following provisions:

"provisions": [
        {
            "holder": "user:user-uuid",
            "source": "project:project-uuid",
            "resource": "cyclades.vm",
            "quantity": 1
        },
        {
            "holder": "project:project-uuid",
            "source": None,
            "resource": "cyclades.vm",
            "quantity": 1
        },
        {
            "holder": "user:user-uuid",
            "source": "project:project-uuid",
            "resource": "cyclades.cpu",
            "quantity": 2
        },
        {
            "holder": "project:project-uuid",
            "source": None,
            "resource": "cyclades.cpu",
            "quantity": 2
        }
]

If any of these provisions fails, i.e. either on the project-level limits or the user-level ones, the whole commission fails.

The astakosclient call issue_one_commission will be adapted to abstract away the need to write both the user-level and the project-level provisions. The previous commission will be issued with:

issue_one_commission(holder="user-uuid", source="project-uuid",
                     provisions={"cyclades.vm": 1, "cyclades.cpu": 2})

The service is responsible to record this resource-to-project association. In Cyclades, each VM, floating IP, or other distinct resource should be linked to a project. Pithos should link containers to projects.

Astakos will handle its own resource astakos.pending_app in a special way: it will always be charged at the user’s base project. This resource is marked with allow_in_projects = False in its definition. Since quota is now project-based, this flag will now be interpreted as forbidding usage in non-base projects.

Resource reassignment

The system will support reassigning a resource to a new project. One needs to specify all related resource values. Astakosclient will provide a convenience function issue_resource_reassignment to construct all needed provisions. For instance, reassigning a VM with two CPUs can be done with:

issue_resource_reassignment(holder="user-uuid",
                            from_source="from-uuid", to_source="to-uuid",
                            provisions={"cyclades.vm": 1, "cyclades.cpu": 2})

This will issue the following provisions to the Quotaholder:

"provisions": [
        {
            "holder": "user:user-uuid",
            "source": "project:from-uuid",
            "resource": "cyclades.vm",
            "quantity": -1
        },
        {
            "holder": "project:from-uuid",
            "source": None,
            "resource": "cyclades.vm",
            "quantity": -1
        },
        {
            "holder": "user:user-uuid",
            "source": "project:from-uuid",
            "resource": "cyclades.cpu",
            "quantity": -2
        },
        {
            "holder": "project:from-uuid",
            "source": None,
            "resource": "cyclades.cpu",
            "quantity": -2
        },
        {
            "holder": "user:user-uuid",
            "source": "project:to-uuid",
            "resource": "cyclades.vm",
            "quantity": 1
        },
        {
            "holder": "project:to-uuid",
            "source": None,
            "resource": "cyclades.vm",
            "quantity": 1
        }
        {
            "holder": "user:user-uuid",
            "source": "project:to-uuid",
            "resource": "cyclades.cpu",
            "quantity": 2
        },
        {
            "holder": "project:to-uuid",
            "source": None,
            "resource": "cyclades.cpu",
            "quantity": 2
        }
]

API extensions

API call GET /quotas is extended to incorporate project-level quota. The response contains entries for all projects for which a user/project pair exists in the quotaholder:

{
    "project1-uuid": {
        "cyclades.ram": {
            "usage": 2147483648,
            "limit": 2147483648,
            "pending": 0,
            "project_usage": ...,
            "project_limit": ...,
            "project_pending": ...
        },
        "cyclades.vm": {
            ...
        }
    }
    "project2-uuid": {
        ...
    }
}

An extra or differentiated call may be needed to retrieve the project quota regardless of user:

GET /quotas?mode=projects

{
    "project-uuid": {
        "cyclades.ram": {
            "project_usage": 2147483648,
            "project_limit": 2147483648,
            "project_pending": 0
        }
        "cyclades.vm": {
            ...
        }
    }
}

All service API calls that create resources can specify the project where they will be attributed.

In cyclades, POST /servers (likewise for networks and floating IPs) will receive an extra argument project. If it is missing, the user’s base project will be assumed. In calls detailing a resource (e.g., GET /servers/<server_id>), the field tenant_id will contain the project id.

Moreover, extra calls will be needed for resource reassignment, e.g:

POST /servers/<server-id>/action

{
    "reassign": {"project": <project-id>}
}

In pithos, PUT and POST calls at the container level will accept an extra optional policy project. The former call assigns a newly created container to a given project, the latter reassigns an existing container. Field x-container-policy-project will be retrieved by a HEAD call at the container level.

User interface

User quota will be presented per project, including the aggregate activity of other project members: the Resource Usage page will include a drop-down menu with all relevant projects. By default, user’s base project will be assumed. When choosing a project, usage for all resources will be presented for the given project in the following style:

                      limit
  used                ^                    taken by others
|::::::|..............|...........|::::::::::::::::::::::::::::::::::|
       ^              ^                                              ^
       usage          effective                                      project
                      limit                                          limit


                      limit
  used                ^          taken by others
|::::::|........|:::::|::::::::::::::::::::::::::::::::::::::::::::::|
       ^        ^                                                    ^
       usage    effective                                            project
                limit                                                limit

Text accompanying the bar could mention usage based on the effective limit, e.g.: usage out of effective limit Virtual Machines. Likewise the shaded used part of the bar could express the same ratio in percentage terms.

Given the above-mentioned response of the /quotas call, the effective limit can be computed by:

taken_by_others = project_usage - usage
effective_limit = min(limit, project_limit - taken_by_others)

Projects show up in a number of service-specific user interactions, too. When creating a Cyclades VM, the flavor-choosing window should first ask for the project where the VM will be charged before showing the available resource combinations. Likewise, creating a new container in Pithos will prompt for picking a project to associate with.

Resource presentation (e.g. Cyclades VMs) will also mention the associated project and provide an action to reassign the resource to a different project.

Command-line interface

Quota can be queried per user or project:

# snf-manage user-show <id> --quota

project  resource    limit  effective_limit usage
-------------------------------------------------
uuid     cyclades.vm 10     9               5

# snf-manage project-show <id> --quota

resource    limit  usage
------------------------
cyclades.vm 100    50

A new command snf-manage project-modify will automate the process of applying/approving applications in order to modify some project settings, such as the quota limits.

Currently, the administrator can change the user base quota with: snf-manage user-modify <id> --base-quota <resource> <capacity>. This will be removed in favor of the project-modify command, so that all quota are handled in a uniform way. Similar to user-modify --all, project-modify will get options --all-base and --all-non-base to allow updating quota in bulk.

Migration steps

Project conversion

Existing projects need to be converted to resource-pool ones. The following steps must be taken in Astakos:

• compute project-level limits for each resource as max_members * member-level limit
• create base projects based on base quota for each user
• make Quotaholder entries for projects and user/project pairs
• assign all current usage to the base projects (both project and user/project entries)
• set usage for all other entries to zero

Cyclades and Pithos should initialize their project attribute on each resource with the user’s base project, that is, the same UUID as the resource owner.

Initial resource reassignment

Once migration has finished, users will be off-quota on their base project, if they had used additional quota from projects. To alleviate this situation, each service can attempt to reassign resources to other projects, following this strategy:

• consult Astakos for projects and quota for a given user
• select resources that can fit in another project
• issue a commission to decrease usage of the base project and likewise increase usage of the available project
• record the new ProjectUUID for the reassigned resources