draft of sharding failover

Author: Andrew Leung

source/administration/sharding-architectures.txt

@@ -151,4 +151,7 @@ Scenarios:
 
 - A :term:`config database` suffers a failure.
 
-  As the :term:`config database` is deployed in a 3 member 
+  As the :term:`config database` is deployed in a 3 member
+  configuration with two-phase commits to maintain synchronization
+  between all members. Any single member failing will not result in a
+  loss of operation