migration: upgrading to replica sets

Author: Sam Kleinman

source/tutorial/convert-standalone-to-replica-set.txt

@@ -20,6 +20,28 @@ administration </replication>`, see:
 - :doc:`/administration/replica-sets`, and
 - :doc:`/applications/replication`.
 
+.. note::
+
+   If you're converting a standalone instance into a replica set that
+   is a :term:`shard` in a :term:`sharded cluster` you must change the
+   shard host information in the :term:`config database`. While
+   connected to a :program:`mongos` instance with a :program:`mongo`
+   shell, issue a command in the following form:
+
+   .. code-block:: javascript
+
+      db.getSiblingDB("config").shards.save( {_id: "<name>", host: "<replica-set>/<member,><member,><...>" } )
+
+   Replace ``<name>`` with the name of the shard, replace
+   ``<replica-set>`` with the name of the replica set, and replace
+   ``<member,><member,><>`` with the list of the members of the
+   replica set.
+
+   After completing this operation you must restart all
+   :program:`mongos` instances. When possible you should restart all
+   components of the replica sets (i.e. all :program:`mongos` and all
+   shard :program:`mongod` instances.)
+
 Procedure
 ---------