introduce PT cluster_id for HA policy targets

Partially implements blueprint node-centric-chain-plugin

Change-Id: Ibeca9d98528d164fd82f22927a87e4532471e6d4

specs/kilo/policy-target-cluster-id.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
+
+==========================================
+Policy Target HA mode
+==========================================
+
+
+Problem description
+===================
+With the introduction of more sophisticated network services and service chaining
+modes, one limitation that we encountered was the impossibility for GBP to describe
+a cluster of HA endpoints, defined as a collection of Policy Target that can freely
+interchange their datapath identity (MAC and IP address) to the end of replacing
+one another whenever the network service requires so (for example, during an HA
+failover).
+
+In the GBP universe, members of the same PTG share the same policy characteristics,
+such as security, quality or connectivity constraints. This however does not cover
+sharing the same network "identity", qualified as Mac or IP address in the datapath.
+We need a way to allow a Policy Target to impersonate another Policy Target in the
+network.
+
+Proposed change
+===============
+The proposal is to introduce a new attribute to the PT description, called
+"cluster_id". A cluster ID is none other but a string which identifies that a specific
+Policy Target belongs to an HA cluster.
+Whenever cluster_id is set, the PTs that share the same cluster identity will be
+able to impersonate one another depending on the backend implementation.
+
+In the reference implementation (Neutron) this is achieved by leveraging Neutron's
+"allowed-address-pair" extension. In the first iteration, for the resource_mapping driver,
+cluster_id will not be allowed to be just any generic string, but a UUID pointing
+to an existing Policy Target. That Policy Target will be identified as the "Master"
+of the cluster. Any member of the cluster will be added the ability to impersonate
+the Master by setting its IP and MAC addresses in the "allowed-address-pair" of
+the member's Neutron Port.
+
+a "Master" PT (defined as a PT pointed by the cluster_id field of another PT) could
+be itseld part of the same cluster (for debugability purpose) although it's not
+mandatory.
+
+By default, this attribute will be only exposed to the Admin role.
+
+
+Data model impact
+-----------------
+
+Policy Target:
+    * cluster_id: String
+
+
+REST API impact
+---------------
+
+Changes to the PT API::
+
+ POLICY_TARGETS: {
+         'cluster_id': {'allow_post': True, 'allow_put': True,
+                        'validate': {'type:string': None},
+                        'default': '', 'is_visible': True}
+ }
+
+Security impact
+---------------
+
+As a Policy Target can now impersonate another PT in the datapath, that includes
+a potential risk when done for malicious reasons. The API however will be open
+only to Admins, and its scope limited in a single PTG (so no Group escape can
+happen).
+
+Notifications impact
+--------------------
+
+When notifying a member of the cluster of a Datapath change, all the cluster's
+members should be notified in order to take coherent action.
+
+Other end user impact
+---------------------
+
+None
+
+Performance impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+Node Drivers' developers can use this API with an admin context in order to
+aggregate PTs for their advanced network services.
+
+Community impact
+----------------
+
+None
+
+Alternatives
+------------
+
+This kind of problem seems to fit very well in the Label or Multi-Group realm,
+to which it can eventually migrate (requires wider discussion)
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+* Ivar Lazzaro (mmaleckk)
+
+Work items
+----------
+
+
+Dependencies
+============
+
+
+Testing
+=======
+
+Tempest tests
+-------------
+
+
+Functional tests
+----------------
+
+
+API tests
+---------
+
+
+Documentation impact
+====================
+
+User documentation
+------------------
+
+None
+
+Developer documentation
+-----------------------
+
+See developer impact
+
+References
+==========
+
+[0] https://github.com/stackforge/group-based-policy-specs/blob/master/specs/kilo/gbp-service-chain-driver-refactor.rst
+[1] http://specs.openstack.org/openstack/neutron-specs/specs/api/allowed_address_pairs.html