Add reporting of capacity factors
This spec outlines the addition of the get pools API response to return the new calculated capacity factors. Change-Id: I8308f5bfcd332a5fd981a16bd1e537040c5c4709
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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===============================================
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Add Capacity Factors to scheduler get pools API
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===============================================
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https://blueprints.launchpad.net/cinder/+spec/add-capacity-factors-to-pool
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This spec proposes adding the new capacity factors in the response to the
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get-pools API request.
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Problem description
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===================
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Typically there is some monitoring and alerting in place against a cinder
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deployment and it's storage array to warn/alert the operator of the cloud
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that they are running out of storage, or are out of storage. The only
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mechanism in Cinder now to see the capacity factors of the backends that cinder
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is managing is to call the cinder api to get-pools. This returns some
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basic information about the backend/pools. But it doesn't really tell the whole
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story.
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The new capacity factors are various aspects of the capacity management that
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cinder calculates on each provisioning request. Each of those factors are
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used at runtime to decide if a volume can land on a particular pool. Those
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factors decide if a pool is full or not depending on several factors including,
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* thin or thick provisioning support
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* total capacity reported by the storage array
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* free capacity reported by the storage array
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* reserved percentage
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* max over subscription ratio
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From those configuration settings and pool capabilities a wider set of factors
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is calculated to determine the capacity availability on a backend/pool. All
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of those factors determine if a backend/pool has space, is running out of space,
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or is out of space for cinder to use.
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Use Cases
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=========
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As an operator of cinder, I want cinder to report all of the factors it uses
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and calculates to determine if cinder's backend/pools have space available.
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Only cinder has all information and the calculate_capacity_factors() can
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create the information the scheduler uses. It should also report that in
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the pools api request, so tooling for monitoring and alerting can be in
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sync with the cinder scheduler.
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Proposed change
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===============
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Add the dictionary that is created from calculate_capacity_factors() to each
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pool information in the get-pools response. The capacity factors are not the
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same thing as the capabilities being reported now. The capacity factors are
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the breakdown of the capacity calculations based on the driver's reported
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capabilities seen by the backend storage. Depending on the capabilities
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in each pool such as thin_provisioning_support and thick_provisioning_support,
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factors will be calculated for each thin and thick if the pool supports.
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.. code-block:: python
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{
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"total_capacity": 5120.0,
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"free_capacity": 4616,
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"reserved_capacity": 1024,
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"total_reserved_available_capacity": 4096,
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"max_over_subscription_ratio": None,
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"total_available_capacity": 4096,
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"provisioned_capacity": 500,
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"calculated_free_capacity": 3596,
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"virtual_free_capacity": 3596,
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"free_percent": 87.79296875,
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"provisioned_ratio": 0.1220703125,
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"provisioned_type": "thick"
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}
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Alternatives
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------------
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The calculate_capacity_factors() function in utils.py can get copy/pasted into
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some external tooling that can do the alerting, but it's subject to getting out
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of sync with cinder's version. Therefore Cinder itself should report all of
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those capacity factors for each backend/pool that it calculates. Then cinder
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will be the definitive answer on the capacity it sees and can use.
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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A new microversion would be required and if compatible cinder
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would return the capacity_factors dictionary in the pools response.
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.. code-block:: console
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GET /v3/{project_id}/scheduler-stats/get_pools?detail=True
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.. code-block:: python
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{
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"pools": [
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{
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"name": "pool1",
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"capabilities": {
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"updated": "2014-10-28T00:00:00-00:00",
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"total_capacity_gb": 1024,
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"free_capacity_gb": 100,
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"volume_backend_name": "pool1",
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"reserved_percentage": 5,
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"driver_version": "1.0.0",
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"storage_protocol": "iSCSI",
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"QoS_support": false,
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"thin_provisioning_support": true,
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"thick_provisioning_support": true,
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},
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"capacity_factors": [
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{
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"total_capacity": 1024,
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"free_capacity": 100,
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"reserved_capacity": 51,
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"total_reserved_available_capacity": 973,
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"max_over_subscription_ratio": None,
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"total_available_capacity": 973,
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"provisioned_capacity": 100,
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"calculated_free_capacity": 873,
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"virtual_free_capacity": 873,
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"free_percent": 89.72,
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"provisioned_ratio": 0.1028,
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"provisioned_type": "thick"
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},
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{
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"total_capacity": 1024,
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"free_capacity": 100,
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"reserved_capacity": 51,
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"total_reserved_available_capacity": 973,
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"max_over_subscription_ratio": 2,
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"total_available_capacity": 1946,
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"provisioned_capacity": 100,
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"calculated_free_capacity": 1846,
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"virtual_free_capacity": 1846,
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"free_percent": 94.86,
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"provisioned_ratio": 0.05,
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"provisioned_type": "thin"
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}
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],
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}
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]
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}
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Security impact
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---------------
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None
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Active/Active HA impact
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-----------------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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hemna (Walter A. Boring IV)
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Work Items
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----------
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* Add new microversion
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* Add ``capacity_factors`` in get-pools API response
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Dependencies
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============
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* This requires the new calculate_capacity_factors() function that is in the
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following review:
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https://review.opendev.org/c/openstack/cinder/+/831247
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Testing
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=======
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Add new unit tests to show the factors being returned in API call.
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Documentation Impact
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====================
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Add documentation to describe the capacity factors and the API response change
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References
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==========
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This was discussed at length at the Zed PTG:
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https://etherpad.opendev.org/p/zed-ptg-cinder
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Youtube Video of discussion:
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https://www.youtube.com/watch?v=6yuOlGckkGE
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The capacity factors definitions
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https://specs.openstack.org/openstack/cinder-specs/specs/queens/provisioning-improvements.html
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