Merge "Add capabilities to storage driver"
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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 capabilities to storage driver
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====================================
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https://blueprints.launchpad.net/glance/+spec/store-capabilities
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This features will enable the static and dynamic ability of a storage driver
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instance based on it's implementation as well as the configuration. The runtime
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status of the backend storage will influence the capacity too.
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Henceforth, ``glance_store`` library can perform proper operations on
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storage as requested by upper layer, e.g. Glance. For example, to enable
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or disable image adding function to glance based on current implementation.
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The store also recognized whether a driver can be reused for all requests
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it handles or if it has to be recreated for each request because it is not
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stateless.
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Problem description
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===================
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The capabilities of store driver can be affected by the following factors:
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1. Status of a connected backend storage.
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2. The deployment configuration.
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3. State of the driver code.
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4. Technically one of capabilities is static whereas the other is dynamic.
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Currently glance_store and glance don't use these capabilities. The driver
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doesn't have a way to expose its capabilities. On the other hand in the store's
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backend handler or client, e.g. glance-{api,registry} there is no common method
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to check these generic operations of the store drivers.
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Currently we observe at least two kind of problems:
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* Some necessary applicability check on the operation related with store
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access are missing, which inhibits the usability of glance service and
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glance_store lib.
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* Hard to implement such check logic neatly, including common check routine
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on these generic operations of store driver, and the check for particular
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feature.
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Proposed change
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===============
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1. Existing drivers need to be updated to expose proper capabilities.
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List of required store capabilities as needed currently.
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+-----------------+---------------------------------------------+
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| Capability Name | Description |
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+=================+=============================================+
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| READ_ACCESS | Generic read access |
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+-----------------+---------------------------------------------+
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| WRITE_ACCESS | Generic write access |
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+-----------------+---------------------------------------------+
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| RW_ACCESS | READ_ACCESS and WRITE_ACCESS |
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+-----------------+---------------------------------------------+
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| READ_OFFSET | Read all bits from a offset |
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| | (Included READ_ACCESS) |
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+-----------------+---------------------------------------------+
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| WRITE_OFFSET | Write all bits to a offset |
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| | (Included WRITE_ACCESS) |
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+-----------------+---------------------------------------------+
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| RW_OFFSET | READ_OFFSET and WRITE_OFFSET |
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+-----------------+---------------------------------------------+
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| READ_CHUNK | Read required length of bits |
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| | (Included READ_ACCESS) |
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+-----------------+---------------------------------------------+
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| WRITE_CHUNK | Write required length of bits |
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| | (Included WRITE_ACCESS) |
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+-----------------+---------------------------------------------+
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| RW_CHUNK | READ_CHUNK and WRITE_CHUNK |
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+-----------------+---------------------------------------------+
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| READ_RANDOM | READ_OFFSET and READ_CHUNK |
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+-----------------+---------------------------------------------+
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| WRITE_RANDOM | WRITE_OFFSET and WRITE_CHUNK |
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+-----------------+---------------------------------------------+
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| RW_RANDOM | RW_OFFSET and RW_CHUNK |
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+-----------------+---------------------------------------------+
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| DRIVER_REUSABLE | driver is stateless and its instance can be |
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| | reused safely |
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+-----------------+---------------------------------------------+
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2. Add common check routine on these generic operations for the store drivers.
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3. Refactoring existing drivers to leverage these capabilities.
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4. Add the logic to recreate driver instance if the storage or driver
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isn't stateless.
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Alternatives
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------------
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None
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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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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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There is no expectation for any obvious degradation in the performance.
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The reason being that there is a simple addition of a checker function
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being triggered in the form of a hook for each store operation, with
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current inclusion of the ('get', 'delete', 'add') operations.
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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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Developers implementing new drivers to the glance_store library would need to
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be aware of this concept. The static and dynamic ability of the storage backend
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could influence their and their implementation design.
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All changes maintain backward-compatibility.
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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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zhiyan (lzy-dev)
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Reviewers
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---------
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Core reviewer(s):
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Nikhil Komawar (nikhil-komawar)
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Stuart McLaren (stuart-mcLaren)
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Work Items
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----------
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* `glance_store change`_
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* `Glance change`_
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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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Necessary unit and functional test cases, will be added into
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glance_store as well as glance.
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Documentation Impact
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====================
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None
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References
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==========
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Corresponding changes:
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* `glance_store change`_
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* `Glance change`_
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.. _glance_store change: https://review.openstack.org/#/c/137416
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.. _Glance change: https://review.openstack.org/#/c/141825
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