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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
+
+=================================================
+Flavor Extra Spec and Image Properties Validation
+=================================================
+
+https://blueprints.launchpad.net/nova/+spec/flavor-extra-spec-image-property-validation
+
+Problem description
+===================
+
+Currently flavor extra-specs and image properties validation are done in
+separate places. If they are not compatible, the instance may fail to launch
+and go into an ERROR state, or may reschedule an unknown number of times
+depending on the virt driver behaviour.
+
+Use Cases
+---------
+
+As an end user I would like to have instant feedback if flavor extra spec or
+image properties are not valid or they are not compatible with each other so
+I can correct my configuration and retry the operation.
+
+Proposed change
+===============
+
+We want to validate the combination of the flavor extra-specs and image
+properties as early as possible once they're both known.
+
+If validation fails then synchronously return error to user.
+
+We'd need to do this anywhere the flavor or image changes, so basically
+instance creation, rebuild, and resize. More precisely, rename
+_check_requested_image() to something more generic, take it out of
+_checks_for_create_and_rebuild(), modify it to check more things and call it
+from all three operations: creation, rebuild, and resize.
+
+.. note:: Only things that are not virt driver specific are validated.
+
+Examples of validations to be added [1]_:
+* Call hardware.numa_get_constraints to validate all the various numa-related
+  things. This is currently done only on _create_instance(), should be done for
+  resize/rebuild as well.
+* Ensure that the cpu policy, cpu thread policy and emulator thread policy
+  values are valid.
+* Validate the realtime mask.
+* Validate the number of serial ports.
+* Validate the cpu topology constraints.
+* Validate the ``quota:*``settings (that are not virt driver specific) in the
+  flavor.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+Due to the new validations, users could face more 4xx errors for more cases
+than we did before in create/rebuild/resize operations.
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+Negligible.
+
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Upgrade impact
+--------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  jackding
+
+Work Items
+----------
+
+* Add validations mostly in nova/compute/api.py.
+* Add/update unit tests.
+* Update documentation/release-note if necessary depending on the new
+  validations added.
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Will add unit tests.
+
+
+Documentation Impact
+====================
+
+None
+
+References
+==========
+
+.. [1] https://docs.openstack.org/nova/latest/user/flavors.html
+
+History
+=======
+
+.. list-table:: Revisions
+   :header-rows: 1
+
+   * - Release Name
+     - Description
+   * - Stein
+     - Introduced