Merge "Persist the RequestSpec object"

specs/liberty/approved/persist-request-spec.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==========================
+Persist RequestSpec object
+==========================
+
+https://blueprints.launchpad.net/nova/+spec/persist-request-spec
+
+Persist the RequestSpec object used for scheduling an instance.
+
+
+Problem description
+===================
+
+There are a few times that it would be useful to have the RequestSpec used for
+originally scheduling an instance where it is not currently available, such as
+during a resize/migrate.  In order to have later scheduling requests operate
+under the same constraints as the original we should retain the RequestSpec for
+these later scheduling calls.
+
+Going forward with cells it will be necessary to store a RequestSpec before an
+instance is created so that the API can return details on the instance before
+it has been scheduled.
+
+Use Cases
+---------
+
+* Operators/users want to move an instance through a migration or resize and
+  want the destination to satisfy the same requirements as the source.
+
+Project Priority
+----------------
+
+Priorities for Liberty have not yet been decided.
+
+
+Proposed change
+===============
+
+A save() method will be added to the RequestSpec object.  This will store the
+RequestSpec in the database.  Since this is also a part of the cells effort it
+will be possible to stor in both the api and regular nova database.  Which
+database it's stored in on save() will be determined by the context used.
+
+Alternatives
+------------
+
+Parts of it could be put into the instance_extra table.  Because later this
+will be persisted in the api database before scheduling and then moved to the
+cell database after scheduling it is beneficial to just store it in a table
+that can exist in both.
+
+Data model impact
+-----------------
+
+A new database table will be added to both the api and cell database.  The
+schema will match what is necessary for the RequestSpec object to be stored.
+Since it is not yet implemented it's of little use to finalize the design here.
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None here, but this will allow for resizes to be scheduled like the original
+boot request.
+
+Performance Impact
+------------------
+
+An additional database write will be incurred.
+
+Other deployer impact
+---------------------
+
+Same as for users, nothing here but this opens up future changes.
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  alaski
+
+Work Items
+----------
+
+ * Add a new table to the api and cell/current database
+ * Add the save() method to the RequestSpec object
+ * Call the save() method in the code at the appropriate place
+
+
+Dependencies
+============
+
+https://blueprints.launchpad.net/nova/+spec/request-spec-object
+
+
+Testing
+=======
+
+New unit tests will be added.  This is not externally facing in a way that
+Tempest can test.
+
+
+Documentation Impact
+====================
+
+Devref documentation will be added explaining the existence of this data for
+use in scheduling.
+
+
+References
+==========
+
+None