multiple instances

onos.rst

@@ -147,7 +147,7 @@ are in turn implemented using a distributed key/value store. The store
 itself will be familiar to anyone that has looked at how modern cloud
 services are designed—it scales across a distributed set of servers,
 and implements the Raft consensus algorithm to achieve fault-tolerance
-in the face of failures. If you are unfamiliar with Raft, a good
+in the event of failures. If you are unfamiliar with Raft, a good
 introduction is available at:
 
 .. _reading_p4:
@@ -671,6 +671,22 @@ The bundle also includes Atomix, although ONOS supports an optional
 configuration that scales the key/value store independently from the
 rest of ONOS.
 
+.. _fig-ha:
+.. figure:: figures/Slide42.png 
+    :width: 600px 
+    :align: center 
+
+    Multiple ONOS instances, all sharing network state via Atomix,
+    provides scalable performance and high availability. 
+
+:numref:`Figure %s <fig-ha>` illustrates ONOS scaled across multiple
+instances, where the set of instances share network state via Atomix
+Maps. The figure also shows each instance being responsible for a
+subset of the underlying hardware switches. Should a given instance
+fail, the remaining instances use the Atomix leader-election primitive
+to select a new instance to take its place, thereby assuring high
+availability.
+
 A refactoring of ONOS to more closely adhere to a microservice
 architecture is also underway. The new version, called µONOS,
 leverages ONOS’s existing modularity, but packages and scales

preface.rst

@@ -21,10 +21,10 @@ organized accordingly. SDN suggests a completely different world-view,
 one that comes with a new software stack. This book is organized
 around that new stack, with the goal of presenting a top-to-bottom
 tour of SDN without leaving any significant gaps that the reader might
-suspect can only be filled with magic or proprietary code. *In fact, we
-invite you do the hands-on programming exercises included at the end
-of the book to prove to yourself that the software stack is both real
-and complete.*
+suspect can only be filled with magic or proprietary code. *We invite
+you do the hands-on programming exercises included at the end of the
+book to prove to yourself that the software stack is both real and
+complete.*
 
 An important aspect of meeting this goal is to use open source. We do
 this in large part by taking advantage of two community-based