Merge "Complete nova support for Glance's v2"
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specs/mitaka/approved/use-glance-v2-api.rst
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specs/mitaka/approved/use-glance-v2-api.rst
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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 for Glance v2 API
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==============================
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https://blueprints.launchpad.net/nova/+spec/use-glance-v2-api
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This spec adds the ability support for Nova to use the Glance v2 API, and start
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the deprecation period for the support of the Glance v1 API.
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While parts of Nova already use the Glance v2 API, this is about making the
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dependency on Glance v1 API optional, so it can be removed completely in a
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future release.
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Problem description
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===================
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Glance relegated v1 from CURRENT to SUPPORTED status in Kilo. Currently Nova
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requires access to the Glance v1 API. Glance would like to deprecate that API,
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so to help that effort Nova should stop using Glance v1 API.
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To allow for a smooth upgrade, we need to ensure Mitaka supports using both
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Glance v1 and Glance v2, to give deployers time to ensure they have Glance v2
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deployed in a way that can be used by Nova.
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While some areas of Nova already make use of Glance v2, there are many areas of
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Nova that still have a hard dependency on Glance v1. The key areas that still
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use Glance v1 include:
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* Nova's Image API, that is effectively just a proxy of Glance's v1 API
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* Virt driver specific download of images and upload of images
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* CRUD operations on image metadata
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* Creating and deleting snapshots in common code.
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Before we can stop Nova requiring Glance v1 and fully deprecate the requirement
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for Glance v1, we need to remove all the above uses of Glance v1.
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Note we must keep compatibility for Glance v1 and Glance v2 to allow for a
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smooth upgrade between releases.
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Note the current version of Glance v2 does not provide an efficient way to
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implement the changes_since parameter that is supported by the current Nova
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Images API. However, Glance have plans to fix that:
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https://blueprints.launchpad.net/glance/+spec/v2-additional-filtering
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Use Cases
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----------
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Currently, Nova deployers are forced to deploy both Glance v1 and Glance
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v2. This is because Nova currently requires Glance v1, but only Glance v2 is
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considered safe to be exposed publicly to End Users.
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It is assumed that Nova's lack of support for Glance v2 is causing confusion
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that is holding people back from deploying Glance v2. This in turn is causing
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some problems for the DefCore effort.
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Project Priority
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-----------------
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None
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Proposed change
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===============
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The number of changes would be minimal to avoid destabilizing. A thorough
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refactor can be done in a follow up spec(s).
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The main bulk of the work is ensuring the Nova Image API contract is maintained
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while talking to either Glance v1 API or Glance v2 API. This will require the
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current Nova Image seam to be capable of talking to both version of the API at
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the same time. Glance API's version discoverability will be used to determine
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whether the v2 of the API is deployed or not. If so, it'll be prefered over v1.
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The second part is looking at other areas in Nova's Glance related
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modules that don't work with the Glance v2 API.
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Once that is completed, there are still some virt driver specific Glance client
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code, but that will be considered a stretch goal, and should not block the
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general deprecation of Glance v1 API support.
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The virt drivers that don't support Glance v2 should fallback to
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v1. Eventually, all drivers should support v2 and Glance's v1 should be turned
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off by default. The expected deadline for this switch is N.
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This spec doesn't intend to change the value of the existing Nova
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configurations for Glance - which include the version in the URL - but rather
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notify the deployer that the new expected value has changed and the
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configuration file should be updated. During the Mitaka cycle, we can strip the
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verion from the URL to discover what versions of the API are deployed and favor
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2 over 1 when possible.
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Alternatives
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------------
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Ideally glanceclient should work as a seam for both Cinder and Nova to use to
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upload and download images, with a stable API. But this is not currently the
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case, and we have waited too long for this support to delay this work any
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further. However, it is assumed that this will exist in the future to avoid
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getting to these situation again.
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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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There will be no impact on the REST API contract. The Nova Image API will
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continue to proxy requests to Glance v1 until the work to bring back
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changes_since is complete.
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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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The deployers should need to be aware that it's possible some virt drivers may
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not support Glance v2 yet. The details of this will be clearly documented in
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the release notes and proper warnings will be logged.
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These drivers will explicitly request v1 to be deployed instead of relying
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entirely on version discoverability
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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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mfedosin
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Other contributors:
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flaper87
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sudipto
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Work Items
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----------
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* Move `nova.image` to be backed by either Glance v1 or Glance v2, defaulting
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to Glance v2. Do this by refactoring the models that consume the images API
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to support Glance v1 and Glance v2.
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* Ensure the rest of the code base can use the existing image code to talk to
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either Glance v1 or Glance v2, again defaulting to Glance v2 when possible.
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* Ensure all the virt drivers either support Glance v2 or fallback to v1.
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* Add a deprecation warning in the logs if users run with Glance v1.
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Dependencies
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============
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Full support for Glance v2 by the Nova Image API is dependent on:
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https://blueprints.launchpad.net/glance/+spec/v2-additional-filtering
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Testing
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=======
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The existing tempest tests will validate the Glance v2 API support, as the
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default will move to Glance v2.
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However, we should also make sure one of the gate jobs still tests the Glance
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v1 only to avoid breaking existing deployments.
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Documentation Impact
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====================
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* Glance API version configuration option needs to be documented
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* Release Notes should note the partial deprecation of Glance v1 support
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* Release Note should warn about any virt drivers that are unable to run with
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Glance v2.
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References
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==========
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None.
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History
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=======
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.. list-table:: Revisions
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:header-rows: 1
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* - Release Name
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- Description
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* - Liberty
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- Introduced
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