Clone CG

This spec proposes to modify the create CG from source API
to take an existing CG as the source, in addition to CG snapshot.

blueprints clone-cg

Change-Id: I087cd527cd553c6f9c9ae87aa888148bc26a7c5f

specs/liberty/clone-cg.rst

@@ -0,0 +1,160 @@
+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+==============================
+Clone Consistency Group
+==============================
+
+https://blueprints.launchpad.net/cinder/+spec/clone-cg
+
+This proposal is to add a feature to create a cloned consistency group
+from an existing one.
+
+Problem description
+===================
+
+Currently a user can create a Consistency Group first and then clone
+one volume from the existing CG at a time and add it to the new CG
+until all volumes are cloned and added to the CG.
+
+The proposal wants to enhance the existing create CG from source API
+and make this a one step rather than multi-step process.
+
+Note: The cloned volumes in the new CG are not guanranteed to be
+consistent. From the consistency point of view, it's no different from
+creating a empty CG first and then creating volume one after another and
+adding to the CG.
+
+The existing Create CG from source API allows user to create a CG from
+the group snapshot (CG snapshot), which should be consistent.
+
+Use Cases
+=========
+
+Suppose a user already has a CG with volumes in it. He/she now wants
+to create another CG with all volumes cloned from the other CG. The
+proposed change will make this much easier for the user.
+
+Proposed change
+===============
+
+* The existing Create CG from Source API takes an existing CG snapshot
+  as the source.
+* This blueprint proposes to modify the existing API to accept an existing
+  CG as the source.
+
+Alternatives
+------------
+
+Without the proposed changes, we can create a CG from an existing CG
+with these steps:
+* Create an empty CG.
+* Create a cloned volume from an existing volume in an existing CG
+  and add to the new CG.
+* Repeat the above step for all volumes in the CG.
+
+Data model impact
+-----------------
+
+* DB Schema Change: A new column source_cg_id will be added to the
+  consistencygroups table.
+
+REST API impact
+---------------
+
+Consistency Group API change
+
+* Create Consistency Group from Source
+  * V2/<tenant id>/consistencygroups/create_from_src
+  * Method: POST
+  * JSON schema definition for V2::
+
+        {
+            "consistencygroup-from-src":
+            {
+                "name": "my_cg",  # existing
+                "description": "My consistency group",  # existing
+                "cgsnapshot_id": "xxxxxxxx",  # existing
+                "consistencygroup_id": "xxxxxxxx",  # new
+            }
+        }
+
+  * In the existing Create Consistency Group from Source API, add a new
+    parameter "consistencygroup_id" to allow an existing CG to be the source
+    of the new CG.
+
+* Cinder Volume Driver API
+  Two new optional parameters will be added to the existing volume driver API:
+    * def create_consistencygroup_from_src(self, context, group, volumes,
+      cgsnapshot=None, snapshots=None, src_group=None, src_volumes=None)
+    * Note only "src_group" and "src_volumes" are new parameters.
+
+Security impact
+---------------
+
+
+Notifications impact
+--------------------
+
+
+Other end user impact
+---------------------
+
+python-cinderclient needs to be changed to support the modified API.
+
+* Create Cloned CG
+  cinder consisgroup-create-from-src --name <name> --description <description>
+  --consistencygroup <cg uuid or name>
+
+Performance Impact
+------------------
+
+
+Other deployer impact
+---------------------
+
+None.
+
+Developer impact
+----------------
+
+Driver developers can add support to this feature in the modified driver API.
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  xing-yang
+
+Other contributors:
+
+Work Items
+----------
+
+1. API change:
+   * Modify Create CG from Source API
+2. Volume Driver API change:
+   * Modify corresponding driver API
+3. DB schema change
+
+Dependencies
+============
+
+Testing
+=======
+
+New unit tests will be added to test the changed code.
+
+Documentation Impact
+====================
+
+Documentation changes are needed.
+
+References
+==========