Instance network info hook

bp instance-network-info-hook

Change-Id: I7267afa07d608eae309e0d1602fb0992f5ad05b7

specs/juno/instance-network-info-hook.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
+
+===============================================
+Add hook for update_instance_cache_with_nw_info
+===============================================
+
+https://blueprints.launchpad.net/nova/+spec/instance-network-info-hook
+
+A hook of the update_instance_cache_with_nw_info call will allow hooks access
+to valuable network information as soon as it becomes available. This will be
+useful for sending this data to scripts that can make informed tweaks to the
+networking on hosts.
+
+Problem description
+===================
+
+Right now there is no way to hook into the updating of network info.
+
+Usecase:
+* Deployer would be able to register a hook to send networking information
+to a script that could make informed tweaks to networking on hosts. This
+might include flows or QoS.
+
+
+Proposed change
+===============
+
+Add a hook to the update_instance_cache_with_nw_info call to allow hooks
+access to this information.
+
+Alternatives
+------------
+
+This information is stored in the database, and could be accessed from there.
+But, this would require giving access to the database to outside applications
+and could potentitally increase load on the database.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+The new code itself will not introduce any performance impact, but due to the
+nature of hooks, any deployer introduced hooks could have a performance impact.
+It will be up to the deployer to test their hooks for performance impact.
+
+Other deployer impact
+---------------------
+
+This change will introduce a new location for hooks. It will not immediately
+effect a deployment, as new hooks would need to be introduced that would
+take advantage of this new hook location.
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  andrew-melton
+
+Other contributors:
+  None
+
+Work Items
+----------
+
+* Register a new hook for update_instance_cache_with_nw_info
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Unit testing to verify that you can register a hook for
+update_instance_cache_with_nw_info should be sufficient. The functional
+testing of the actual hooks should be left to the deployer.
+
+
+Documentation Impact
+====================
+
+If there is a list of hook locations, it will need to be updated to include
+this new location.
+
+References
+==========
+
+* Dev docs on nova hooks: http://docs.openstack.org/developer/nova/devref/hooks.html
+