Cinder Count API

Problem description

There is no current API that can retrieve summary count data for volumes and search filters. For example, getting the total number of volumes that match a given filter criteria (for example, all volumes in a given state). Retrieving all volumes and then manually determining the count data does not scale.

Use Case

A UI dashboard that contains volumes in various states. A new API is needed to retrieve the volume count data associated with various filters (ie, volumes in available state, volumes in error state, etc.)

Proposed change

The new count API will accept that same filter values as the existing /volumes API and re-use the existing filter processing (once the common parts are refactored into utility methods that can be re-used). However, instead of retrieving all of the volumes, only the number of matching volumes will be retrieved from the database and returned.

The new API will requires the following changes:

• volume_get_count function in db\sqlalchemy\api.py that accepts a dict of filters (just like the existing volume_get_all function) and returns in integer. The query object will be constructed in the same manner that it is for the filter processing, but then the count() function will be invoked to return the integer count.
• volume_get_count function in db\api.py that accepts a dict of filters and returns in integer
• a get_count function on the API class in volume\api.py. The same filter processing done in the get_all function will be applied on the new function.

Alternatives

Other APIs exist that return count data (quotas and limit) but they do not accept filter values.
I cannot think of alternative implementations. I believe that we want this new API to mimic the existing /volumes API in how the filters are processed into the database query object.

REST API impact

URL: v2/​{tenant_id}​/volumes/count

• Description: Returns the number of Block Storage volumes that the tenant who submits the request can access.
• Method Type: GET
• Normal http response code(s): 200
• Expected error http response code(s): TBD, same as the existing /volumes API
• Parameters: "all_tenants" will be used to signify that volumes from all tenants should be queried (admin only). Same filter values will be supported that the existing /volumes API supports.
• JSON reply:

{ "count": 5 }

Other End user impact

python-cinderclient could be updated to expose this but it is not required.

Deployer impact

None.

Developer impact

None.

Implementation

Assignee(s): Steven Kaufer
Other contributors: None

Milestones

Targetted for: Juno Originally approved for: Unknown Completed: None

Work Items

• Creating the new count functions in the volume\api.py layer and in the database layers
• Exposing this function with an API extension

Dependencies

None.

Testing

Unit testing to ensure that the correct count value is retrieved for various filters.

Documentation Impact

API Documentation for new the API.