Provision for immediate caching of an image
Change-Id: Ieb793afaa6bf4b7c21729408654ec316ba45d816
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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Provision for immediate caching of an image
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===========================================
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Include the URL of your launchpad blueprint:
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https://blueprints.launchpad.net/glance/+spec/instant_caching
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Provision for immediate caching of a given image on a particular glance node.
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Problem description
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===================
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In Yoga we have added support for caching related operations under V2 API, but
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still we need to depend on existing periodic job to cache the actual image.
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This means user/deployer/admin needs to wait until next periodic job to run
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for caching of an actual image. Even though default time for periodic job is
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300 seconds (5 minutes) it may vary deployment wise and the user has to wait
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until the actual image is cached.
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Proposed change
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===============
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We are proposing to remove existing periodic job from glance-api and modify
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existing ``PUT /v2/cache/{image_id}`` API which will queue an image for caching
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and start caching it immediately. If any existing instant caching operation is
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in progress then the latest image will be added to the queue so that it will
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be picked up for caching as soon as previous operation completes. User can use
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``GET /v2/cache`` API call to see the size of the queue.
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Alternatives
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------------
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Instead of modifying existing API, we can add a new POST API which will start
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immediate caching of specified image. We can use existing policy `cache_image`
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so that user with appropriate permissions can perform this operation. To make
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the policy compatible with secure RBAC we need to pass required parameters
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like ImageTarget while enforcing the policy. It is recommended to keep
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`cache_image` operation limited to admin use only.
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Another alternative solution could be, instead of removing the old periodic
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job, the new API should trigger the periodic job instantly to cache all the
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images rather than just caching a specified image at a time. This
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solution need to be thread safe as there might be a chance of existing
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periodic job is already running or new periodic job will start running while
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we trigger the same via API.
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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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Caching is and will remain local to each glance node and as this command
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will be executed remotely, operator needs to know the direct URL of
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each glance node which are behind the load balancer. Operator needs to
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provide this direct URL to glanceclient so that client should hit
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particular node to trigger immediate caching on that node.
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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 or abhishekk
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Other contributors:
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None
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Reviewers:
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cyril-roelandt/rosmaita/jokke/pdeore/mrjoshi
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Work Items
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----------
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* Modify existing API (PUT /v2/cache/{image_id})
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* Remove the 'cache_prefetcher_interval' config option and related tests.
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* Modify documentation, update API reference
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* Tempest coverage for Caching operations
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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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* All new cache API should be tested using tempest tests
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Documentation Impact
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====================
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* The API documentation will need to be updated
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* Need to update Cache documentation as well with new information
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References
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==========
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* https://docs.openstack.org/glance/victoria/admin/cache.html
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