Add conductor_group docs

Change-Id: I7c4281c6b02392470600acca3d7ca84eb33af0c2

doc/source/admin/conductor-groups.rst

@@ -0,0 +1,66 @@
+.. _conductor-groups:
+
+================
+Conductor Groups
+================
+
+Overview
+========
+
+Large scale operators tend to have needs that involve creating
+well defined and delinated resources. In some cases, these systems
+may reside close by or in far away locations. Reasoning may be simple
+or complex, and yet is only known to the deployer and operator of the
+infrastructure.
+
+A common case is the need for delineated high availability domains
+where it would be much more efficient to manage a datacenter in Antarctica
+with a conductor in Antarctica, as opposed to a conductor in New York City.
+
+How it works
+============
+
+Starting in ironic 11.1, each node has a ``conductor_group`` field which
+influences how the ironic conductor calculates (and thus allocates)
+baremetal nodes under ironic's management. This calculation is performed
+independently by each operating conductor and as such if a conductor has
+a ``[conductor]conductor_group`` configuration option defined in its
+`ironic.conf` configuration file, the conductor will then be limited to
+only managing nodes with a matching ``conductor_group`` string.
+
+.. note::
+   Any conductor without a ``[conductor]conductor_group`` setting will
+   only manage baremetal nodes without a ``conductor_group`` value set upon
+   node creation. If no such conductor is present when conductor groups are
+   configured, node creation will fail unless a ``conductor_group`` is
+   specified upon node creation.
+
+.. warning::
+   Nodes without a ``conductor_group`` setting can only be managed when a
+   conductor exists that does not have a ``[conductor]conductor_group``
+   defined. If all conductors have been migrated to use a conductor group,
+   such nodes are effectively "orphaned".
+
+How to use
+==========
+
+A conductor group value may be any case insensitive string up to 255
+characters long which matches the ``^[a-zA-Z0-9_\-\.]*$`` regular
+expression.
+
+#. Set the ``[conductor]conductor_group`` option in ironic.conf
+   on one or more, but not all conductors::
+
+    [conductor]
+    conductor_group = OperatorDefinedString
+
+#. Restart the ironic-conductor service.
+
+#. Set the conductor group on one or more nodes::
+
+    openstack baremetal node set \
+        --conductor-group "OperatorDefinedString" <uuid>
+
+#. As desired and as needed, remaining conductors can be updated with
+   the first two steps. Please be mindful of the constraints covered
+   earlier in the document related to ability to manage nodes.

doc/source/admin/index.rst

@@ -25,6 +25,7 @@ the services.
    Emitting Software Metrics <metrics>
    Auditing API Traffic <api-audit-support>
    Service State Reporting <gmr>
+   Conductor Groups <conductor-groups>
    Upgrade Guide <upgrade-guide>
    Security <security>
    Troubleshooting FAQ <troubleshooting>