Notification Support for Metadata Definitions

We are proposing to support notifications for events on the
Metadata Definitions Catalog.

Implements: blueprint metadefs-notifications

Change-Id: I73a0921b8cf66cbaeffed285fcbc04a9aaee3c43
Co-Authored-By: Lakshmi N Sampath <lakshmi.sampath@hp.com>
Co-Authored-By: Kamil Rykowski <kamil.rykowski@intel.com>

specs/kilo/metadefs-notifications.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
+
+=============================================
+Notification Support for Metadata Definitions
+=============================================
+
+https://blueprints.launchpad.net/glance/+spec/metadefs-notifications
+
+This blueprint adds metadata definition notification support.
+
+The implemented juno spec for metadata notifications is here for reference:
+
+http://specs.openstack.org/openstack/glance-specs/specs/juno/metadata-schema-catalog.html
+
+Problem description
+===================
+
+Metadata definition resources - namespaces, objects, properties,
+tags, and resource types - don't provide any notification events when
+certain operations are performed on them. This doesn't allow for any
+intelligent caching of the data, meaning that the only opportunity for
+catalog users to be aware of changes is to continually poll. Polling is not
+performant for catalog users and puts extra load on the API and database.
+
+Proposed change
+===============
+
+We are proposing to support notifications for events on the
+Metadata Definitions Catalog.
+
+This implementation will include the following events that will be
+triggered when necessary:
+
+* metadef_namespace.create - namespace has been created
+* metadef_namespace.update - namespace has been updated
+* metadef_namespace.delete - namespace has been deleted
+* metadef_object.create - object has been created
+* metadef_object.update - object has been updated
+* metadef_object.delete - object has been deleted
+* metadef_property.create - property has been created
+* metadef_property.update - property has been updated
+* metadef_property.delete - property has been deleted
+* metadef_tag.create - tag has been created
+* metadef_tag.update - tag has been updated
+* metadef_tag.delete - tag has been deleted
+* metadef_resource_type.create - resource type has been added to namespace
+* metadef_resource_type.delete - resource type has been removed from namespace
+
+In addition we will add a new configuration option to allow for disabling
+individual notifications.  It will be a comma separated list with the
+following syntax::
+
+    disabled_notifications = <type>.<action>
+
+For example, the following would disable all tag notification and property
+deletions::
+
+    disabled_notifications = metadef_tag,metadef_property.delete
+
+The notifier will read this configuration and ignore notifications that are
+in the disabled list.
+
+The reason for this proposed addition is that we aren't sure whether or not
+tag notifications could get too chatty for some reason.  Therefore,
+we'd like to give an option for deployers to disable it.
+
+Alternatives
+------------
+
+No notification support could be added.  In this event,
+constant polling for changes could be done.  The constant polling would lead
+to both latency in getting updates and extra load on the API and database.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+No external API impacts will be visible.  The API itself will have a notifier
+added as part of the call.
+
+Security impact
+---------------
+None
+
+Notifications impact
+--------------------
+A notifier will be added to the REST API calls.  The notifications listed
+above will be added. A new configuration option will be added to disable
+specific notifications.
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+Additional notifications will be generated, but the amount of changes to
+metadata definitions are not anticipated to be enough to impact performance.
+
+However we want to add the new disabled_notifications configuration option to
+allow operators to disable the notifications if they determine that are too
+chatty.
+
+Other deployer impact
+---------------------
+Deployers will have to setup listeners to received notification on metadefs
+if they desire them.
+
+Developer impact
+----------------
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+ kamil-rykowski
+
+Other contributors:
+ none
+
+Reviewers
+---------
+
+Core reviewer(s):
+  jokke
+
+Other reviewer(s):
+  lakshmi-sampath
+  travis-tripp
+
+Work Items
+----------
+
+Changes would be made to:
+
+#. Glance v2 metadef APIs to add notifiers
+#. notifer
+#. gateway
+
+Dependencies
+============
+
+Need to sync openstack/common from oslo-incubator for service module.
+
+https://bugs.launchpad.net/glance/+bug/1413861
+
+Testing
+=======
+
+Unit tests will be added for all possible code with a goal of being able to
+isolate functionality as much as possible.
+
+Tempest tests will be added wherever possible.
+
+Documentation Impact
+====================
+
+Docs needed for new notification usage
+
+References
+==========
+
+`Current glance metadata definition catalog documentation.
+<http://docs.openstack.org/developer/glance/metadefs-concepts.html>`_