Add spec for gathering share usage size
We need to have a way to gather information about actual share storage usages, so cloud operators could use this information for billing. Partially-Implements BP share-usage-size Change-Id: I2fe98a75b5a70559086dc4b78cbd935383710c57
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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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Share usage size tracking
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=========================
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https://blueprints.launchpad.net/manila/+spec/share-usage-size
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We need to have a way to gather information about actual share storage usages,
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so cloud operators could use this information for billing, health checks
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and/or other purposes.
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Problem description
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===================
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Currently, it is impossible to get actual storage usage of some specific
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share, hence, it is impossible to bill for storage usage. It is only possible
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to bill for quota limits.
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Use cases
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=========
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* Manila could report storage usages to metering services like ceilometer [1].
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* Some storage backends do not reserve whole requested share size right away
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after share creation and just set quota/limit for shares, for such backends
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it may be more suitable to bill for usage, not limit/quota.
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Proposed change
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===============
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Add the periodic task in share service for gathering the shares usage size.
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The periodic task will be invoked after the share manager starts up. We
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can set the interval time that determines how often the share manager will
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poll the driver to perform the next step of get share usage size.
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Administrators and driver developers can "opt-in" to enable this feature
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in their drivers and in their clouds.
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Add notifiers for shares usage size we want to measure. Right now we intend
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to add notifiers to resouces (such as: shares, share groups, snapshots and
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etc) and publish the resouces we expect [1].
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The update_share_usage_size() driver method is a new driver method which will
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be called after driver initialization and in the periodic task, that returns a
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dictionary about shares id and shares usage size. The shares usage size value
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info will be notified to ceilometer or other project, otherwise the share info
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doesn't need to be notified.
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Alternatives
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------------
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* Why we don't gather the space usage when we need to use it (such as: list,
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show APIs)?
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Because we could publish such real time information to ceilometer.
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* Why we don't store the space usage?
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Because we can't implement this inside manila without duplicating
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functionality already in other projects like ceilometer.
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It's a number that changes over time. If the number is too old, it might
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be wildly inaccurate. So we're going to push the storage/retrieval parts
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of the problem outside of manila to keep manila's scope small and focused.
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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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None
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CLI impact
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----------
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None
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Driver impact
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-------------
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* Get real share provisioned capacity from driver::
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def update_share_usage_size(self, context, shares):
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"""Invoked to get the usage size of given shares.
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Driver can use this method to update the share usage size of
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the shares. To do that, a dictionary of shares should be
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returned.
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:shares: None or a list of all shares for updates.
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:return None or a dictionary of updates in the format::
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{
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'09960614-8574-4e03-89cf-7cf267b0bd08': {
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'used_size': '200',
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},
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}
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"""
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raise NotImplementedError()
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If an administrator has configured a backend for monitoring and the driver
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cannot support the update_share_usage_size method, then the share manager will
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catch the raise exception (NotImplementedError) from the driver, and we will
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later not invoke the periodic task to update share usage size for shares of
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this backend. We will LOG that it is unsupported instead.
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Security 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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Collecting share usage have a negative service performance impact.
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When the size of a share is known at the moment of creation and does not
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change without an explicit extend or shrink, we don't have to collect usage
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at all. Now we have to collect usage. It could be costly.
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Administrators may set the periodic interval configuration option value to
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a large interval or disable it if necessary. It could be less costly or not
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costly.
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Other deployer impact
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---------------------
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We will need to add an option for enabling and disabling sending notifications.
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This flag will affect manila deployed with any backend.
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By default, this option will be set to false and manila won't be sending
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notifications, keeping the behavior it currently has.
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If operators want to start retrieving metrics on the manila shares usage size,
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they will need to enable sending notifications on the configuration file after
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upgrade to or installation of Pike. They also need to make sure they have a
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specified version of ceilometer or other software deployed. After this, the
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feature here specified will be available for use.
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Developer impact
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----------------
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This will require a change on the driver interface. To support this feature,
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drivers will need to implement the ``update_share_usage_size`` feature.
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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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* zhongjun(jun.zhongjun2@gmail.com)
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Work items
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----------
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* Implement the core feature with functional tempest test
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coverage
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* Add documentation of this feature
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Dependencies
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============
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None
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Testing
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=======
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* Unit tests
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* Functional tempest tests
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Documentation impact
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====================
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- Devref
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- API reference
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- User guide and Admin guide
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References
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==========
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[1] https://specs.openstack.org/openstack/manila-specs/specs/pike/ceilometer-integration.html
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