Architecture section in Read the Docs

Added first draft for architecture section

Change-Id: I29679a6625758258bae5c77a8b31a4b1ad418f45
Issue-Id: SDC-508
Signed-off-by: Idan Amit <ia096e@intl.att.com>
diff --git a/docs/architecture.rst b/docs/architecture.rst
index 8daa0d3..4e20a3e 100644
--- a/docs/architecture.rst
+++ b/docs/architecture.rst
@@ -1,6 +1,7 @@
 .. This work is licensed under a Creative Commons Attribution 4.0 International License.
 .. http://creativecommons.org/licenses/by/4.0
 
+============
 Architecture
 ============
 
@@ -14,14 +15,45 @@
    
    * This note must be removed after content has been added.
 
+SDC As Part of ONAP
+===================
+
+.. image:: images/SDC_In_ONAP.png
+
+
+High Level Architecture
+=======================
+
+The following diagram shows the high-level relationship between the system components:
+
+.. image:: images/High_Level_Architecture_SDC.png
+
+The SDC architecture uses the Jetty server as an application server.
+
+- The *Jetty front end*:
+   - supplies the static content of web pages, and all resources that required by the GUI
+   - serves as a proxy for the REST API requests coming from the GUI
+   
+  Every request originating from the GUI is passed to the Jetty front-end server before it is executed.
+
+- The *Jetty back end* containes all the logic for the SDC.
+
+SDC uses two storage components: Elastic Search(ES) and Cassandra
+
+- *Elastic Search* is used to index the auditing data received from different operations in the SDC.
+
+  This information can then be analyzed with Kibana. The *Kibana server* enables statistical analysis of the operations done, according to the business logic.
+  
+- *Cassandra* is used to store auditing data, artifacts and data model objects.
+
 
 Capabilities
-------------
+============
 
 
 Usage Scenarios
----------------
+===============
 
 
 Interactions
-------------
+============