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Quota for Magnum Resources

Launchpad blueprint:

https://blueprints.launchpad.net/magnum/+spec/resource-quota

There are multiple ways to slice an OpenStack cloud. Imposing quota on these various slices puts a limitation on the amount of resources that can be consumed which helps to guarantee "fairness" or fair distribution of resource at the creation time. If a particular project needs more resources, the concept of quota, gives the ability to increase the resource count on-demand, given that the system constraints are not exceeded.

Problem description

At present in Magnum we don't have the concept of Quota on Magnum resources as a result of which, as long as the underlying Infrastructure as a Service(IaaS) layer has resources, any user can consume as many resources as they want, with the hardlimit associated with the tenant/project being the upper bound for the resources to be consumed. Quotas are tied closely to physical resources and are billable entity and hence from Magnum's perspective it makes sense to limit the creation and consumption of a particular kind of resource to a certain value.

Use cases

Alice is the admin. She would like to have the feature which will give her details of Magnum resource consumption so that she can manage her resource appropriately.

  1. Ability to know current resource consumption.
  2. Ability to prohibit overuse by a project.
  3. Prevent situation where users in the project get starved because users in other project consume all the resource. Alice feels something like "Quota Management" would help to gurantee "fairness".
  4. Prevent DOS kind of attack, abuse or error by users where an excessive amount of resources are created.

Proposed change

Proposed change is to introduce a Quota Table which will primarily store the quota assigned to each resource in a project. For Mitaka, we will restrict the scope to a Bay, which are Magnum resources. Primarily, as a first step we will start of by imposing quota on number of bays to be created in a project. The change also plans to introduce REST API's to GET/PUT/POST/DELETE. CLIs to get information of Quota for a particular project will also be provided.

For Mitaka, we will restrict the scope of the resources explicit created and managed by Magnum. Specifically for Mitaka we will focus on number of Bays only. Going ahead we might add Quota for containers, etc. The resources of which a Bay is constructed out of is inherently not only Magnum resource but involve resource from Nova, Cinder, Neutron etc. Limiting those resource consumption is out of the scope of this spec and needs a close collaboration with the quota management framework of the orchestration layer, since the orchestration layer can invoke the respective IaaS projects API's and get the consumption details before provisioning. As of now the orchestration layer used by Magnum, Heat, does not have the concept of Quota, so we will start with imposing Quota on resources which Magnum manages, Bay, more specifically for Mitaka.

When a project is created and if the Magnum service is running, the default quota for Magnum resources will be set by the values configured in magnum.conf. Other Openstack projects like Nova1, Cinder2 follow a similar pattern and we will also do so and hence won't have a seperate CLI for quota-create. Later if the user wants to change the Quota of the resource option will be provided to do so using magnum quota-update. In situation where all of the quota for a specific Magnum resource (Bay) have been consumed and is under use, admin will be allowed to set the quota to a any value lower than the usage or hardlimit to prohibit users from the project to create new Bays. This gives more flexibility to the admin to have a better control on resource consumption. Till the time the resource is not explicitly deleted the quota associated with the project, for a particular resource, won't be decreased. In short quota-update support will take into consideration the new hardlimit for a resource, specified by the admin, and will set the new value for this resource.

Before the resource is created, Magnum will check for current count of the resource(Bays) created for a project. If the resource(Bay) count is less than the hardlimit set for the Bay, new Bay creation will be allowed. Since Bay creation is a long running operation, special care will be taken while computing the available quota. For example, 'in-progress' field in the Quota usages table will be updated when the resource(Bay) creation is initiated and is in progress. Lets say the quota hardlimit is 5 and 3 Bay's have already been created and two new requests come in to create new Bays. Since we have 3 Bays already created the 'used' field will be set to 3. Now the 'in-progres' field will be set to 2 till the time the Bay creation is successful. Once the Bay creation is done this field will be reset to 0, and the 'used' count will be updated from 3 to 5. So at this moment, hardlimit is 5, used is 5 and in-progress is 0. So lets say one more request comes in to create new Bay this request will be prohibited since there is not enough quota available.

For Bays,

available = hard_limit - [in_progress + used]

In general,

Resource quota available = Resource hard_limit - [ (Resource creation in progress + Resources already created for project)]

Alternatives

At present there is not quota infrastructure in Magnum.

Adding Quota Management layer at the Orchestration layer, Heat, could be an alternative. Doing so will give a finer view of resource consumption at the IaaS layer which can be used while provisioning Magnum resources which depend on the IaaS layer3.

Data model impact

New Quota and Quota usages table will be introduced to Magnum database to store quota consumption for each resource in a project.

Quota Table :

Field Type Null Key Default Extra
id created_at updated_at project_id resource hard_limit int(11) datetime datetime varchar(255) varchar(255) int(11) NO YES YES YES NO YES

PRI

MUL

NULL NULL NULL NULL NULL NULL auto_increment

Quota usages table :

Field Type Null Key Default Extra
created_at updated_at id project_id resource in_progress used datetime datetime int(11) varchar(255) varchar(255) int(11) int(11) YES YES NO YES NO NO NO PRI MUL NULL NULL NULL NULL NULL NULL NULL auto_increment

REST API impact

REST API will be added for :

  1. quota-defaults List all default quotas for all tenants.
  2. quota-show List the currently set quota values for a tenant.
  3. quota-update Updates quotas for a tenant.
  4. quota-usage Lists quota usage for a tenant.
  5. quota-list List quota for all the tenants.

A user with "admin" role will be able to do all the above operations but a user with "non-admin" role will be restricted to only get/list quota associated to his/her tenant. User with "non-admin" role can be a Member of the tenant less "admin" role.

REST API for resources which will have quota imposed will be enhanced :

1. Bay create Will check if there is quota available for Bay creation, if so proceed ahead with the request otherwise throw exception that not enough quota is available.

Security impact

None

Notifications impact

None

Other end user impact

End user will have the option to look at the quota set on the resources, quota usage by a particular project.

Performance Impact

None

Other deployer impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee: vilobhmm

Other contributors: None

Work Items

  1. Introduce Quota and Quota usages table in Magnum database.
  2. Introduce API to set/update Quota for a resource, specifically bay, for Mitaka release.
  3. Introduce API to create Quota entry, by default, for a resource.
  4. Provide config options that will allow users/admins to set Quota.
  5. Make sure that if the resource is deleted the used count from the quota_usages table will be decremented by the number of resources deleted. For example, if resource, bay, is deleted then the entries for it in the Quota usages table should be decremented by the number of Bays deleted.
  6. Provide CLI options to view the quota details :
    1. magnum quota-show <project-id>
    2. magnum quota-update <project-id> <resource> <hard-limit>
    3. magnum quota-defaults <project-id>
    4. magnum quota-usage <project-id>
    5. magnum quota-list
  7. Add conf setting for bays default quota since we will focus on Bays for Mitaka.

Dependencies

None

Testing

  1. Each commit will be accompanied with unit tests.
  2. Gate functional tests will also be covered.

Documentation Impact

None

References


  1. https://github.com/openstack/nova/blob/master/nova/quota.py

  2. https://github.com/openstack/nova/blob/master/cinder/quota.py

  3. http://lists.openstack.org/pipermail/openstack-dev/2015-December/082266.html