Support region for openstack actions

Change-Id: I51f07d42a6c28f6310cf9f9724c99be0c0eaea04
Implements: blueprint mistral-multi-region-support

specs/pike/approved/mistral-multi-region-support.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
+
+===================================
+Support region in OpenStack actions
+===================================
+
+Launchpad blueprint:
+
+https://blueprints.launchpad.net/mistral/+spec/mistral-multi-region-support
+
+This blueprint intends to support specifying region name for OpenStack
+actions, so that authorized user could run OpenStack actions within different
+OpenStack regions in one workflow, which is extremely userful for operators
+when they want to execute maintainance tasks across different regions within
+one workflow.
+
+
+Problem description
+===================
+
+Currently, Mistral end user could specify region name or target region name
+when running OpenStack workflow, which means all the tasks inside the workflow
+have to be running within that specific region. It's impossible to run
+different tasks in different regions.
+
+Use Cases
+---------
+
+* User with credential in region-1 can specify region-2 for the whole
+  workflow (Keystone is shared between different regions).
+
+* User with credential in region-1 can specify different region in different
+  tasks.
+
+
+Proposed change
+===============
+
+The basic idea is simple, support 'region' as an extra input param for all
+OpenStack actions.
+
+1. Add a config option called ``modules_support_region``, the value will be
+   list of module names for which the 'region' input param will be add to each
+   of its actions. The reason for adding this option is, there may be some
+   OpenStack services (e.g. Keystone) already support region(or similar
+   concept) in action input params, we should not add a param with same
+   meaning, e.g. if Keystone is shared between regions in OpenStack
+   deployment, 'keystone' should be excluded from the list.
+
+2. Insert 'region' as an optional input param when registering OpenStack
+   actions.
+
+Alternatives
+------------
+
+As mentioned in the problem description section, it's impossible to do multi-
+region workflows without this feature.
+
+Data model impact
+-----------------
+
+This change doesn't have to influence the data model.
+
+REST API impact
+---------------
+
+None.
+
+End user impact
+---------------
+
+With this change, users could specify region name as action input.
+
+Performance Impact
+------------------
+
+None.
+
+Deployer impact
+---------------
+
+When upgrade, deployer should run ``tools/sync_db.py`` script to delete all
+OpenStack actions and re-create again. 'region' will be added as input param
+automatically.
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  Lingxian Kong <anlin.kong@gmail.com>
+
+Work Items
+----------
+
+* Add 'region' as action input param for modules specified in
+  ``modules_support_region`` options. Use 'region' to construct OpenStack
+
+* service client.
+
+
+Dependencies
+============
+
+None.
+
+
+Testing
+=======
+
+* write tests to make sure 'region' is supported for configured OpenStack
+  modules.
+
+* write tests to make sure 'region' is properly used to construct OpenStack
+  service client.
+
+
+References
+==========
+
+None.