663f7beb7f
blueprint cells-instance-groups-api-db Change-Id: Ie5f9cbbf28c3b105ea7d02bc5d6ab97a1db9c04d
160 lines
3.9 KiB
ReStructuredText
160 lines
3.9 KiB
ReStructuredText
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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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CellsV2 - Instance Groups API DB migrations
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===========================================
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https://blueprints.launchpad.net/nova/+spec/cells-instance-groups-api-db
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Instance group tables that currently reside in the cell database must be
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migrated to the API database. Instance groups are exposed in the API and
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generally accessed in the scheduler.
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Problem description
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===================
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Use Cases
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---------
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Users wish to create instance groups that operate globally across deployments
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without worrying about cells implementation.
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Proposed change
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===============
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New ``instance_groups`` and ``instance_group_policy`` and
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``instance_group_member`` tables will be created in the API database. The
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models for these will closely match the existing models in the nova database
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but they will no longer have soft delete.
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Methods currently located in ``db/sqalchemy/api.py`` will be mirrored in
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``objects/instance_group.py`` and modified to access the API database. The
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``InstanceGroup`` and ``InstanceGroupList`` objects will be modified to
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access the API database initially and the fall-back to the cell database
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if neccessary. ``InstanceGroupList`` methods will return items from both
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the cell and API databases. These methods will, if-neccessary remove duplicates
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from the returned items.
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Migration methods will be created to move data from the cell to API database.
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These migration methods will be added to the ``online_data_migrations``
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nova manage command.
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The ``Flavor`` tables have already been migrated to the API db. In general
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the proposed changes will follow those methods. [1]_
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Alternatives
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------------
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It may be possible to leave the ``instance_group_member`` table in the
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cell database as this table will grow with the number of instances.
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The ``InstanceGroup`` function ``get_hosts`` accesses the
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``instance_group_member`` table. It is used in both the scheduler and the
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compute manager for affinity. As this table is generally accessed outside
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of the cells it is likely that there would be a greater performance hit
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from placing this in the cell database.
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Data model impact
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-----------------
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There will be a large data model impact as many new tables will be created
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in the API database. The data models have been omitted as they are essentially
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unchanged from those currently in the cell database.
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REST API impact
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---------------
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None
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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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Deployers must be aware of the ``nova-manage`` command that will perform
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one time data migration for the tables mentioned.
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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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<mjdoffma@us.ibm.com>
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Other contributors:
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None
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Work Items
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----------
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* Create a new database table and database migration for ``instance_groups``
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, ``instance_group_policy`` and ``instance_group_members``.
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* Modify functions in ``InstanceGroup`` and ``InstanceGroupList`` to
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access the API database.
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* Create migration functions for the affected tables and add these to
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``online_data_migrations`` command.
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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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* Unit tests for API database access functions.
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* Functional tests for data migration of instance group tables.
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Documentation Impact
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====================
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Documentation must mention the one time data migration tool in
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the ``nova-manage`` command and the data that is migrated.
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References
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==========
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.. [1] https://blueprints.launchpad.net/nova/+spec/flavor-cell-api
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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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* - Newton
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- Introduced
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