[Spec] Add weight for each glance store
Change-Id: I56f9485bfe025962d3d657352260b62db7cab750
This commit is contained in:
Abhishek Kekane
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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 support to configure weight for each store
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==============================================
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https://blueprints.launchpad.net/glance-store/+spec/store-weight
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Add support to configure weight to each store. The store with highest
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weight will be given preference to download the image.
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Problem description
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===================
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Since introduction of importing single image into multiple stores or copying
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existing image into multiple stores, single image can be stored at multiple
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locations or different stores configured by glance. Current download image
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is based on the default ``location_strategy`` which is ``location_order``,
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traverse through the image locations one by one if there are multiple
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locations (in this case it will return the image stored at the first
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location). If user prefers to download the image from a specific store then
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they can use ``store_type`` as location strategy to give preference to
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download the image from that store only. For example if ``location_strategy``
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is set as ``store_type`` and ``store_type`` has `rbd` as preference then
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the image will be downloaded from the `rbd` store only. Now the problem with
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``store_type`` location strategy is that there can be multiple stores of same
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type (multiple rbd or file stores). So again user will not able to download
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the image from the specific store even if ``location_strategy`` is set to
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``store_type``.
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Consider the following use cases for providing download from specific
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store support:
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* I have a large image and want to download it from the SSD store
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since it's fast.
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* I do multiple concurrent downloads on a particular image so
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want to download it from the RELIABLE store since the i/o
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handling is better.
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Proposed change
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===============
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This proposal requires changes in glance_store as well as in glance.
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Glance store side change:
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Add new configuration option ``weight`` default to zero for each store.
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Operator can change it for each store if they wish. The store with highest
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weight will be given preference to download the image from.
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.. code-block:: none
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[default]
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enabled_backends = robust:rbd,cheap:file
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[robust]
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rbd_store_pool=images
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weight=10
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[cheap]
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filesystem_store_datadir=/opt/stack/data/glance/images/
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weight=5
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In above example, `robust` store will always be a preferred store to download
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the image from. If image is not available in `robust` store then it will be
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searched in `cheap` store which is next inline.
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If no weight is provided for stores (i.e. all stores have default weight `0`)
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then the image will be searched based on image creation order (similar as
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``location_order``).
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Glance side change:
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Once glance_store side changes are implemented then we need to modify
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``GET`` API of image to sort the image locations based on the `wegith`
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assigned to each store. If `weight` is default then the location
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order will not be changed.
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Alternatives
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------------
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Add new location strategy 'store_identifier' to existing default two
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strategies. This will add comma separated list of store identifiers which
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will be given preference to download the image from. New configuration
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option ``store_identifier_preference`` under group
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``store_identifier_location_strategy`` will be added where user/deployer
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can reference their preferences based on store identifiers.
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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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None
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Other deployer impact
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---------------------
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Deployer/Operator need to configure `weight` for each glance-store.
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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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dansmith
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Other contributors:
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abhishek-kekane
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Work Items
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----------
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* Add new configuration option `weight` for each store
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* GET API change to sort locations based on store `weight`
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* Unit and functional tests
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* Tempest coverage
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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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Sufficient unit/functional and tempest tests will be added.
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Documentation Impact
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====================
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Need to document how location order will be changed based on weight
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assigned to each store.
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References
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==========
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None
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@ -13,3 +13,12 @@
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:maxdepth: 1
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glance/*
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2023.2 approved specs for glance store:
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.. toctree::
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:glob:
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:maxdepth: 1
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glance_store/*
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