Allow evacuation without target host
This feature will let the scheduler pick up the best target compute node when evacuating an instance. bp find-host-and-evacuate-instance Change-Id: I100987e8f6159267e0203ee6bd97aaa524d6620e
This commit is contained in:
Leandro I. Costantino
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specs/juno/find-host-and-evacuate-instance.rst
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specs/juno/find-host-and-evacuate-instance.rst
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..
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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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API: Evacuate instance to a scheduled host
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===========================================
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https://blueprints.launchpad.net/nova/+spec/find-host-and-evacuate-instance
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The aim of this feature is to let operators evacuate instances without
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selecting a target host manually. The scheduler will select the best
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target instead.
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Problem description
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===================
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In the event of a unrecoverable hardware failure (compute-node down),
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Operators need to evacuate the instances by selecting a target
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compute host.
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This may work for temporary pre-selected failover-hosts, but if they
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just want to evacuate/rebuild the instance without taking further
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action, Operators must check each instance/flavor metadata and select
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target hosts that match the specs individually for each evacuation.
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In case of using external tools to trigger the evacuation, logic about
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the compute-hosts has to be there to appropriately call the API.
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It also make it consistent with migrate and live-migrate operations.
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Proposed change
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===============
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Modify the current rebuild_instance flow to let the scheduler pick up the best
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target host for the instance being evacuate.
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Alternatives
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------------
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Something external to pick up the proper host when
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nova can already do it.
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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 current evacuate API v2/v3 will be modified to accept body data without
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target host field and this change will be advertised through a new
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extension ExtendedEvacuateFindHost in case of v2.
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If the field is present but empty old behavior will be applied to be
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able to determine if it's an missing due to input error or not.
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* Evacuate an instance to another compute-host.
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* POST
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* Normal Response Code: 200
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* Expected error http response code(s)
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- 404: Compute host (if provided)/instance not found
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- 400: Compute service in use
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- 409: Invalid instance state
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* v2|v3/servers/id/action
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* Schema definition for V3::
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evacuate = {
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'type': 'object',
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'properties': {
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'evacuate': {
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'type': 'object',
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'properties': {
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'on_shared_storage': parameter_types.boolean,
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'admin_password': parameter_types.admin_password,
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},
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'required': ['on_shared_storage']
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'additionalProperties': False,
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},
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},
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'required': ['evacuate'],
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'additionalProperties': False,
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}
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* Sample request::
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{ "evacuate": { "adminPass": "%(adminPass)s",
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"onSharedStorage": "%(onSharedStorage)s" }}
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* Sample Response::
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{ "adminPass": "%(password)s" }}
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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 target_host argument as
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optional.
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The user can trigger this feature by:
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nova evacuate my_server
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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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leandro-i-constantino
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Other contributors:
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juan-m-olle
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Work Items
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----------
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* Move rebuild instance to conductor task to unify rebuild/evacuate logic
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* Add logic to select target host
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* Add APIv2/v3
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* Set target-host optional on nova-client
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* Allow evacuating instances in an 'affinity' group, allowing the scheduler to
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pick the destination
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Dependencies
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============
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For a complete use-case the following bp will be required
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https://blueprints.launchpad.net/nova/+spec/validate-targethost-live-migration,
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since we can retrieve the original scheduler hints from that a particular
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instance and let the scheduler select the best host based on that.
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Until then, instances launched without any scheduler hint could still be
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selected by the scheduler by using flavor specs.
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Testing
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=======
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Tempest do not currently support multi-node tests, so it will be added
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after CI can run those kind of tests.
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Documentation Impact
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====================
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* Api Docs to reflect that host field is now optional. If not present
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in the body the new feature will be triggered.
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* Client docs ( due to optional arg)
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* Admin User Guide on evacuation topic.
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References
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==========
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None
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