Spec for Glance cache API
APIImpact Change-Id: I05133d61f52b0fa5f39f6a976356789cd1ef5940
This commit is contained in:
Cyril Roelandt
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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Cache API
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=========
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https://blueprints.launchpad.net/glance/+spec/cache-api
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Managing split deployments is currently a bit difficult and sometimes require
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operators to run commands on multiple nodes. Introducing a cache API would make
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managing such deployments easier.
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Problem description
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===================
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Adding new API endpoints related to caching would prove beneficial in two ways:
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* Along with the planned work on cluster awareness, this would make it easier to
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manage split deployments (multiple glance-api nodes on different locations)
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* Users would have to deal with fewer commands since the
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glance-cache-prefetcher is now part of glance-api as a periodic job and
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glance-cache-manage will now be part of python-glanceclient.
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Proposed change
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===============
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The main change this specification describes is the extension of the Glance API
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to handle cache-related operations. The goal is to have an API that can replace
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the "glance-cache-manage" tool. These are the operations we would like to
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support:
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* List cached,queued images
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* Delete cached, queued images
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* Delete all cached and queued images using single API call
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* Queue image for prefetching
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At the moment to enable the glance caching in the deployment operator needs
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to configure two different middleware, `cache` and `cachemanage`. `cache`
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middleware is responsible for configuring cache resources such as cache
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directory, initializing cache driver etc. whereas `cachemanage` middleware
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used to deal with actually caching resources via glance-api. As caching
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now will be part of glance V2 API, we would like to deprecate `cachemanage`
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middleware and remove it as per `deprecation and removal` policy. The newly
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added cache endpoints will be ``EXPERIMENTAL`` in this cycle and will be
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marked as stable in following cycle.
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In addition to above proposed change this will introduce three new policies
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`cache_image`, `cache_list` and `delete_cache` so that user with appropriate
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permissions can perform these operations. We will also deprecate the existing
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`manage_image_cache' policy in favor of new policies. To make the new
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policies compatible with secure RBAC we need to ensure to pass required
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parameters like ImageTarget while enforcing the new policies. It is recommended
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to keep `cache_image`, `cache_list` and `delete_cache` operations limited to
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admin use only.
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Alternatives
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------------
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If we do nothing about cluster awareness and we do not provide an easy-to-use
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API for cache management, operators could probably write homemade solutions to
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aggregate data from multiple nodes, but this would be error-prone and not
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user-friendly.
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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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This spec proposes the following new endpoints:
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**New API**
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* List cached and queued images
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* Delete a cached or queued image
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* Delete all cached or queued images
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* Queue image for caching
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**Common Response Codes**
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* Create Success: `201 Created`
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* Delete Success: `204 No Content`
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* Failure: `400 Bad Request` with details.
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* Forbidden: `403 Forbidden`
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**[New API] List cached or queued images**
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List all images cached or queued for caching on this node::
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GET /v2/cache
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{
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"cached_images": [
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{
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"id": "d75b9181-e1ce-45b4-8147-fb66fc4ea82f",
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"last_accessed": 1560451015.977297,
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"last_modified": 1560451015.977297,
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"size": 12345,
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"hits": 42,
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"checksum": "6788146b9d3fddc8dd03d86bfe9239b0"
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},
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],
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"queued_images": [
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"id": "d75b9181-e1ce-45b4-8147-fb66fc4ea82f",
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]
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}
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Response codes:
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* 200 -- Upon authorization and successful request. The response body
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contains the JSON payload with the cached and queued images.
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**[New API] Delete a queued or cached image**
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Delete a specific image from the cache::
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DELETE /v2/cache/{image_id}
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Response codes:
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* 204 -- The image was deleted
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* 403 -- Permission denied
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**[New API] Delete all queued or cached images**
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Delete all queued or cached images::
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DELETE /v2/cache
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Response codes:
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* 204 -- The cache was purged
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* 403 -- Permission denied
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**[New API] Queue an image for caching**
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Pre-cache an image::
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PUT /v2/cache/{image_id}
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Response codes:
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* 202 -- The request has been accepted, the image will be queued for caching
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* 403 -- Permission denied
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* 404 -- Image not found
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Security impact
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---------------
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As described in proposed change section either existing policies or
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new policies will be enforced to avoid security breach.
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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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The glance client should be updated, with new commands:
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* glance cache-list
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* glance cache-image <IMAGE-ID>
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* glance cache-delete <IMAGE-ID>
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* glance cache-delete-all
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Provision will be made to pass direct URL (host:port) to these commands
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which will direct the call to particular glance node. Implementation
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details for the same will be described in specific glance-client spec.
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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 will be local to each glance node and as these commands will be
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executed remotely, operator needs to know the direct URL of each glance
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node which are behind the load balancer. Operator need to provide this
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direct URL to glanceclient so that client should hit particular node
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to retrieve the cache information of 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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jokke
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Other contributors:
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cyril-roelandt
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Work Items
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----------
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* Deprecate `cachemanage` middleware
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* Add new cache endpoint (/v2/cache)
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* Make new policies compatible with secure RBAC
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* Add python-glanceclient support
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* Deprecate glance-cache-manage
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* Deprecate glance-cache-prefetcher
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* Modify documentation, update API reference
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* Devstack support to enable cache on remote node
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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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* The new API endpoints 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 commands
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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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