Enable cold migration with target host
The target host can be specified when cold migrating a server. And a new request body field called ``force`` (defaulted to False) is added in order not to call the scheduler when providing a destination. Setting it to 'True' makes the cold migrate operation bypass the scheduler. APIImpact Change-Id: I57f3cb045a5f050931dc6c0fe9786ddd7dd0a2d7 blueprint cold-migration-with-target-ocata
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Takashi NATSUME
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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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Enable cold migration with target host - Ocata
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==============================================
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https://blueprints.launchpad.net/nova/+spec/cold-migration-with-target-ocata
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The aim of this feature is to let operators cold migrate instances with
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target host manually.
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In addition, provide a way to make sure that resource allocation is
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consistent for the cold migration operation when a destination host
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is specified.
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Problem description
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===================
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A target host can be specified on the live migration operation.
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And there is a scheduler rule check and 'force' flag in REST API
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when a target host is specified on the live migration operation.
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But a target host cannot be specified on the cold migration operation.
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It is inconsistent with them.
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Use Cases
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---------
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It is same as the live migration use case.
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Sometimes an operator or a script decides which host is the best
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suited to accept a cold migration and then wants to perform it.
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A consistency with a live migration case should be ensured.
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Proposed change
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===============
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Modify the API and the current resize_instance flow to be able to
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specify the target host for cold migration.
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Add the function to check whether a destination host is
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in accordance with scheduler rules or not in cold migration
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as a default behaviour.
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Specifically to say, add setting 'requested_destination' of the RequestSpec
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object in nova/compute/api.py. The field has already been supported
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in the scheduler, so it just need to be filled in.
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This blueprint also provides a way for operators to bypass the scheduler,
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we will make the API for cold migration including a destination host
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by adding an request body argument called 'force'
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(accepting True or False, defaulted to False) and
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the corresponding CLI methods will expose that force option.
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If the microversion asked by the client is older than the version
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providing the field, then it won't be passed
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(neither True or False, rather the key won't exist)
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to the conductor so the conductor won't call the scheduler.
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Alternatives
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------------
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None
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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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* URL: POST /v2.1/servers/{server_id}/action
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JSON request body::
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{
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"migrate": {
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"host": "target-host",
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"force": True
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}
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}
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The 'host' parameter to specify a target host is required
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(not optional) because of consistency with a live migration API.
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If 'force' is True, do not check the destination.
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If 'force' is False or null or not provided,
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do check the destination.
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If 'force' is supplied in the request body and its value is true
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but the 'host' parameter is null,
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then an HTTP 400 Bad Request will be served to the user.
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Microversion is bumped up.
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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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python-novaclient will be modified to have a target host argument as
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optional. And add the 'force' argument as optional.
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nova migrate [--force True] <server> [<host>]
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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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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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natsume-takashi
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Work Items
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----------
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* Add logic to specify target host for cold migration
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* Add processing checking destination host in the cold migration
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* Add API with bumping a new microversion
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* Add a target host argument and 'force' argument on novaclient
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* Add nova functional tests
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* Add tempest tests
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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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Add the following tests.
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* Unit tests
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* Functional tests
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* Tempest tests
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Documentation Impact
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====================
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* API Reference
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* CLI Reference
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* Admin User Guide on cold migration topic.
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References
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==========
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* [1] enable cold migration with target host
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- https://blueprints.launchpad.net/nova/+spec/cold-migration-with-target
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History
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=======
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The function to specify a target host was previously approved in juno[1].
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The function to check whether a destination host is in accordance
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with scheduler rules or not and the 'force' flag are added for ocata.
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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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* - Ocata
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- Introduced
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