rollback mechanism

Change-Id: I699761f76bffc96fc22ae8ee5bb010c405a0b3a6
Implements: blueprint rollback-mechanism

specs/ussuri/approved/rollback-mechanism.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
+
+===================
+Rollback Mechanism
+===================
+
+https://blueprints.launchpad.net/watcher/+spec/rollback-mechanism
+
+
+Problem description
+===================
+
+After every audit, there would be one actionplan to execute. The actionplan
+is a group of actions, such as:
+
+ * migrations
+ * change nova service state
+ * change node power state
+ * ...
+
+Sometimes, the users want to rollback one actionplan even after the actionplan
+successfully executed.
+
+To tester, they usually make the env unbalance, so that there will be
+instances migration during audit. After that they need to migrate
+the instances back to the source host for next test.
+
+Moreover, for host maintenance, it will migrate all instances from the
+maintaining host to others. After the host maintenance and active again,
+there is no mechanism to migrate the instances automatically back to the
+maintaining host.
+
+Use Cases
+----------
+
+As a QA of Watcher, I want to rollback the actionplan, so that I can easily
+restore the environment for next test.
+
+As an openstack operator, I want to migrate the instances back to the source
+node after the node having been executed "host maintenance" strategy.
+
+Proposed change
+===============
+
+In watcher-api, we can add 'rollback' action to ActionPlan API. When the api
+recieves the rollback request and then distributes the request to
+watcher-decision-engine module.
+
+In watcher-decision-engine, it retrives the actionplan and records every
+rollback of the actions which belong to the actionplan, then return the
+rollback result to watcher-api.
+
+Because the compute data model changes by time, the actionplan is possible to
+rollback failed. To make the rollback mechanism to work as far as possible,
+only recent(default, recent in one hour) actionplan is allowed to rollback.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+Rollback Action Plan
+
+* /v1/action_plans/{actionplan_ident}/rollback
+
+  * Method type: POST
+
+  * actionplan_ident：UUID of the Action Plan
+
+  * Normal http response code(200)
+
+  * Expected error http response code(400,404)
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  <sue>
+
+Work Items
+----------
+
+* ActionPlan rollback action API
+
+* RollBack mechanism for one actionplan
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Unit tests
+
+Documentation Impact
+====================
+
+* Add documentation about how to use the new feature
+
+References
+==========
+
+None
+
+History
+=======
+
+.. list-table:: Revisions
+   :header-rows: 1
+
+   * - Release Name
+     - Description
+   * - Ussuri
+     - Introduced