Add server group support

This spec introduces server group concept to Mogan.

Partially Implements: bp server-group-api-extension
Change-Id: Iab90dcb0a5d080f204c8f923e4bc4bd0675d9ebe

specs/pike/approved/server-group-api-extension.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
+
+============
+Server Group
+============
+
+https://blueprints.launchpad.net/mogan/+spec/server-group-api-extension
+
+This spec proposes adding server group support to mogan. It's quite like
+nova's server groups, but nova only support *host* based affinity or
+anti-affinity, which is not fit for bare metals.
+
+
+Problem description
+===================
+
+Currently, it is not possible to schedule some servers to the same or
+different location or group like what nova server group does for virtual
+machines.
+
+Use Cases
+---------
+
+* As a tenant, I would like to schedule servers on the same group of bare metal
+  nodes.
+
+* As a tenant, I would like to schedule servers on the different group of bare
+  metal nodes.
+
+Proposed change
+===============
+
+We proposes to add a special aggregate metadata key *affinity_zone*. You may
+define it as failure domains(e.g., by power circuit, rack, room, etc), or
+whatever you want to make affinity and anity-affinity happen in such groups.
+All bare metals nodes are in a same affinity zone by default.
+
+* A new mogan.objects.ServerGroup object would be added to the object model.
+
+* Add a set of APIs to allow tenants manage the server groups, including
+  create, delete, show and list APIs.
+
+* Allow users to specify server group when claiming servers.
+
+* Add logic to scheduler to check the server group plicy and members affinity
+  relationship to filter nodes.
+
+Alternatives
+------------
+
+None
+
+Data model impact
+-----------------
+
+The proposed change will be adding the following fields to the server group
+object with their data type and default value for migrations.
+
++-----------------------+--------------+-----------------+
+| Field Name            | Field Type   | Default Value   |
++=======================+==============+=================+
+| id                    | Integer      | None            |
++-----------------------+--------------+-----------------+
+| uuid                  | UUID         | None            |
++-----------------------+--------------+-----------------+
+| user_id               | UUID         | None            |
++-----------------------+--------------+-----------------+
+| project_id            | UUID         | None            |
++-----------------------+--------------+-----------------+
+| name                  | String       | None            |
++-----------------------+--------------+-----------------+
+| policies              | ListOfString | None            |
++-----------------------+--------------+-----------------+
+| members               | ListOfString | None            |
++-----------------------+--------------+-----------------+
+
+REST API impact
+---------------
+
+REST API will be changed as part of this change.
+
+- To create a new server group, a user will::
+
+    POST /v1/server_groups
+
+  With a body containing the JSON description of the server group.
+
+  JSON Schema::
+
+    {
+        "type": "object",
+        "properties": {
+            'name': {'type': 'string', 'minLength': 1, 'maxLength': 255},
+            'policies': {
+                'type': 'array',
+                'items': [{
+                    'type': 'string',
+                    'enum': ['anti-affinity', 'affinity']}],
+                'uniqueItems': True,
+                'additionalItems': False,
+            },
+        },
+        'required': ['name', 'policies'],
+        'additionalProperties': False,
+    }
+
+- To list server groups, a user will::
+
+    GET /v1/server_groups
+
+- To show server group details, a user will::
+
+    GET /v1/server_groups/{servergroup_id}
+
+- To delete a server group, a user will::
+
+    DELETE /v1/server_groups/{servergroup_id}
+
+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:
+  liusheng
+
+Other contributors:
+  zhenguo
+
+Work Items
+----------
+
+* Add server group object with the proposed fields.
+* Add REST API to support server group management.
+* Change scheduler to consider the specified server group.
+* Allow users to specify server group when claiming servers.
+* Change CLI to support server group management.
+* Add UT and docs.
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+Unit Testing will be added.
+
+Documentation Impact
+====================
+
+Docs about server groups will be added.
+
+References
+==========
+
+None