Merge "Add spec for Share Migration Ocata improvements"
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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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Share Migration Ocata Improvements
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==================================
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https://blueprints.launchpad.net/manila/+spec/ocata-migration-improvements
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Proposal for Share Migration improvements and changes, based on
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Barcelona Summit feedback.
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Problem description
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===================
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At Barcelona Summit we gathered feedback on Share Migration Experimental API
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feature `[1]`_. There were a few improvements suggested:
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* For driver-assisted migration, drivers may be able to migrate a share and its
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snapshots, but the API layer is blocking the request when there are
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snapshots.
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* There has been a lot of debate on whether the default value of non-disruptive
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parameter should be True or False. Currently it is also inconsistent with all
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other driver-assisted related parameters, defaulting to False while all the
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other driver-assisted parameters default to True.
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* The driver-assisted migration API parameters could be greyed out in the
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manila-ui "Start Migration" form so users better understand that "Force
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Host-assisted migration" negates the effects of the others.
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* Currently the API does not immediately return an error on the obvious
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incorrect combination of "Force host-assisted migration" and other
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driver-assisted parameters set to True. This will be useful for when the
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manila-ui is not used.
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* The driver-assisted migration API parameters' descriptions in manila-ui and
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python-manilaclient could be improved to state that these parameters are
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"Enforced", as opposed to "not preserving metadata" when these properties
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are not selected.
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* Currently the Share Migration API prevents migrations to the same
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storage pool. This prevents the cases of migrating shares between share
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servers or simply retyping. In such cases, it may be desired for the share to
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remain in the same storage pool, while being able to change the share's type
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or share network (and consequently the share server in the latter).
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Use Cases
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=========
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The implementation of the changes suggested addresses existing problems and
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enables use cases as seen below:
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* Migrating shares along with snapshots
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* Better user experience when choosing the API parameters
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* Load balancing among share servers
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* Retyping a share
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Proposed change
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===============
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This spec proposes:
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1) Removing the snapshot restriction from the API layer, change it to work just
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like the other parameters' validation (writable, preserve_metadata, etc),
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thus adding an additional entry for migration_check_compatibility driver
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interface. Add the parameter to the API layer, named "preserve_snapshots".
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Also, this parameter, as the other ones, is not applicable for the
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host-assisted migration, preventing it from running if enabled.
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2) Changing all REST API parameters to be mandatory, except for "force
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host-assisted migration". The purpose is to have better REST API support in
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the future, defaulting non-existing new REST API parameters to false when
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older microversions are used, and to avoid data loss in cases where the
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administrator does not specify a parameter by accident. For more
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information, see reference `[2]`_.
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3) Grey out the driver-assisted options in manila-ui when "Force host-assisted
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migration" is selected.
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4) Return an error when "Force host-assisted migration" API parameter is set
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along with other driver-assisted migration API parameters.
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5) Improve the driver-assisted API parameters' descriptions in manila-ui and
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python-manilaclient to include "Enforce ..." in the name. Example: "Enforce
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Writable". Please note that this will not change the parameter name.
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6) Changing the validation that rejects the API request when the parameters are
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the same as the source share to do so only when the combination of "new
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share network", "new share type" and "destination pool" are the same.
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Alternatives
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------------
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An alternative solution has been discussed with regards to proposal #2 above,
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where all options would be changed to False. This will imply that the default
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migration-start command will be able to run the host-assisted migration if the
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driver-assisted approach is unsupported or fails. We decided not to take this
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approach because we wanted above all else to avoid surprises when performing
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migration. We also considered defaulting all the driver-assisted parameters to
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True, to avoid the surprise situation, but that would compromise the sanity of
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the REST API with regards to future updates. We addressed these concerns by
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insisting that clients always send a value of True or False for each option.
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For more details see `[2]`_.
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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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* The microversion will be bumped to include the changes proposed.
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* The changes proposed will update the migration_start API as follows:
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- (POST, 202, 400, 409) migration-start: migrates share
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URL: /shares/<share_id>/action
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Body::
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{
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'migration_start': {
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'force_host_assisted_migration': false,
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'preserve_metadata': true,
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'writable': true,
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'nondisruptive': true,
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'preserve_snapshots': true,
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'host': 'ubuntu@generic2#GENERIC2',
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'new_share_type_id': 'foo_share_type_id',
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'new_share_network_id': 'bar_share_network_id'
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}
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}
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* This API will not return an error immediately anymore when a share has
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snapshots, unless the "Force host-assisted migration" API parameter option
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is set.
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* Not specifying any value for "nondisruptive", "preserve_snapshots",
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"writable" or "preserve_metadata" will now return error 400.
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* The same pool API restriction will be changed to not allow the same
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combination of "destination host", "share network" and "share type" as the
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source share.
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* Specifying "force_host_assisted_migration" as True, along with any of
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"writable", "preserve_metadata", "preserve_snapshots" or "nondisruptive"
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being True, will also result in error 400, as it would be an incompatible
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combination.
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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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This proposal will require updates to python-manilaclient. See example::
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manila migration-start <share> <host> <nondisruptive> <writable>
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<preserve_metadata> <preserve_snapshots> --force-host-assisted-migration
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--new-share-network --new-share-type
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manila migration-start share_1 ubuntu@generic1#GENERIC1 True True True True
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Please note that during code implementation we may decide to change the syntax
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shown in the example above with regards to the mandatory driver-assisted
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parameters, in order to drive a better user experience with the CLI.
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As for manila-ui, there will be a new checkbox "Preserve Snapshots".
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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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None
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Developer impact
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----------------
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None
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Driver impact
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-------------
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Driver maintainers will be prompted to update their driver-assisted migration
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"migration_check_compatibility" implementation according to the new API
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parameter 'preserve_snapshots' introduced. In this change, it will be added to
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the existing implementations as "False".
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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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ganso
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Work Items
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----------
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* Implement main patch for manila that includes:
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- Updated Tempest tests
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- Updated Unit tests
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- API changes described in this proposal
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- Share migration host-assisted and driver-assisted changes required
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* Implement additions and changes in python-manilaclient with:
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- Unit tests
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- Functional tests
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* Implement additions and changes in manila-ui with:
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- Unit tests
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* Update documentation for this feature (see `Documentation Impact`_ section)
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Dependencies
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============
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No previous dependencies on other Ocata patches so far
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Testing
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=======
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- Unit tests in manila, manila-ui and python-manilaclient
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- Tempest API tests in manila and python-manilaclient
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_`Documentation Impact`
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=======================
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- Docstrings
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- Release notes
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- Developer reference
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- Admin reference
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- API reference
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References
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==========
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_`[1]` https://etherpad.openstack.org/p/ocata-manila-contributor-meetup
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_`[2]` http://lists.openstack.org/pipermail/openstack-dev/2016-November/107186.html
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