Add project/user association to placement

https://blueprints.launchpad.net/nova/+spec/placement-project-user

This cycle we are changing the quota system to count resources to check quota instead of tracking usage and reservations separately. As things currently stand, we must query cell tables to count things like cores and ram to check against quota limits. There are a couple of problems with the current approach:

  1. Querying all cells for instances owned by a project and summing their cores and ram counts is not efficient.

  2. Quota usage becomes effectively “freed” if contact with one or more cells is lost for any reason, until the cells return.

To address these problems, we propose adding project and user associations to placement for consumers.

Problem description

With the current resource counting approach, placement allocated resources such as cores and ram must be counted by querying for instances owned by a project in all cells and summing their cores and ram. The counts could be more efficiently obtained if placement stored project/user associations for resource consumers and we could query placement for allocations based on project/user and resource classes.

There is also the problem of relying on cell databases for allocated resource counts. If the API cell loses contact with a cell for some reason (network issue, cell maintenance, transient cell database issue, etc), the resources for that cell cannot be counted. The down cell’s resources then become omitted from the counted usage for the project/user, allowing them to allocate additional resources in other cells in the meantime. If and when the down cell returns, the project/user could then have allocated more resources than their allowed quota limit.

Use Cases

As an administrator of an OpenStack multiple cell environment, it’s important that my users not be able to exceed their allocated quota limits when cells are down.

Proposed change

Add a consumers table for placement that stores project/user associations for consumers with fields: consumer_id, project_id, user_id:

CREATE TABLE consumers (
    id INT UNSIGNED NOT NULL AUTOINCREMENT PRIMARY KEY,
    consumer_id VARCHAR(36) NOT NULL,
    project_id VARCHAR(255) NOT NULL,
    user_id VARCHAR(255) NOT NULL,
    INDEX (project_id, consumer_id),
    INDEX (project_id, user_id, consumer_id)
);

The records should have the same lifetime as allocations records.

The queries for usages for a project/user will look like:

GET /usages?project_id=<uuid>
GET /usages?project_id=<uuid>&user_id=<uuid>

In placement, when a query is received it will look up the consumer_ids and matching allocations by querying the consumers table joined with the allocations table on consumer_id and return the summarized usages.

After the usages are returned from placement, the quota counting code can use them to check against quota limits.

Alternatives

Another way to associate project/user with allocations would be to add project_id and user_id columns to the allocations table. It would be more direct than creating a consumers table with the associations but it wouldn’t be as generic. A consumers table could potentially be used for queries other than just allocations.

Data model impact

The following data model changes will be needed:

  • New models for: Consumer

  • New database table for Consumer

  • Database migration will be needed to add the consumers table to the schema.

REST API impact

A new REST resource: /usages will be added and the GET method will accept query strings in the URI called ‘project_id’ and ‘user_id’ that will return usages matching the project_id and user_id. A usage is a sum of allocations that match the project_id and user_id, per resource class. The addition of the REST resource will require a new placement API microversion.

Example:

GET /usages?project_id=<uuid>

The response would be:

200 OK
Content-Type: application/json

{
  "usages": {
    "VCPU": 2,
    "MEMORY_MB": 1024,
    "DISK_GB": 50,
    ...
  }
}

The PUT method of /allocations/{consumer_uuid} will be changed to accept ‘project_id’ and ‘user_id’ as required properties on payload as part of the same new placement API microversion described earlier. They are considered to be required because allocations are going to be written by either a human/user or on behalf of a human/user, as a privileged API action. In the case of the resource tracker, the project_id and user_id are easily obtained from the Instance object.

Example:

ALLOCATION_SCHEMA = {
  "type": "object",
  "properties": {
    "allocations": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "resource_provider": {
            "type": "object",
            "properties": {
              "uuid": {
                "type": "string",
                "format": "uuid"
              }
            },
            "additionalProperties": False,
            "required": ["uuid"]
          },
          "resources": {
            "type": "object",
            "patternProperties": {
              "^[0-9A-Z_]+$": {
                "type": "integer",
                "minimum": 1,
              }
            },
            "additionalProperties": False
          }
        },
        "required": [
          "resource_provider",
          "resources"
        ],
        "additionalProperties": False
      }
    },
    "project_id": {
      "type": "string",
      "minLength": 1,
      "maxLength": 255
    },
    "user_id": {
      "type": "string",
      "minLength": 1,
      "maxLength": 255
    }
  },
  "required": [
    "allocations",
    "project_id",
    "user_id"
  ],
  "additionalProperties": False
}

Security impact

None.

Notifications impact

None.

Other end user impact

None.

Performance Impact

Performance of quota resource counting should be more efficient with the new API over querying all cells for instances owned by a project and iterating over them, summing the cores and ram values. Instead of N database queries for N cells, there will be one database query by placement of consumers associated with a project/user joined on allocations to get the matching allocations, which will be summed to represent usages. Performance will also be improved in that cells being temporarily down will no longer have the potential for end users to exceed allowed quota limits.

Other deployer impact

None.

Developer impact

None.

Implementation

Assignee(s)

Primary assignee:

melwitt

Other contributors:

None

Work Items

  • Fix bug 1679750 where allocations are not cleaned up upon local delete https://bugs.launchpad.net/nova/+bug/1679750

  • Create database migration that creates the consumers table

  • Update AllocationList object to read/write the consumers table

  • Add a new REST resource: /usages for the placement REST API to query usages by project_id and user_id as part of a new placement API microversion

  • Add ‘project_id’ and ‘user_id’ as required properties on the allocations PUT request schema as part of the same new placement API microversion

  • Update the resource tracker to send project_id and user_id when setting allocations in placement

  • Bump the service version and add a conditional for whether to call placement for counting cores and ram usage, based on the service version. During an upgrade, old computes will be writing allocations without project_id and user_id, so we can’t rely on placement for usage until all computes have been upgraded. Existing allocation records will self-heal when upgraded computes update them as part of the nova-compute periodic task: update_available_resource.

Dependencies

The quota counting spec is a foundation for this work, since the need for the project/user association and updates to the allocations REST API is based on counting resources for checking quota.

Testing

New unit tests for the migration and changes to the AllocationList object will be added. Gabbi functional tests will be added to test the new request parameters in the allocations REST API and the new /usages REST resource.

Documentation Impact

The placement-api-ref will be updated to document the new /usages REST resource and the new required request parameters for the PUT method of the /allocations/{consumer_uuid} REST API.

History

Revisions

Release Name

Description

Pike

Introduced