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+.. This work is licensed under a Creative Commons Attribution 4.0
+   International License. http://creativecommons.org/licenses/by/4.0
+   
+.. _docs_Datalake_Handler_MS:
+
+Architecture
+------------
+
+
+Background
+~~~~~~~~~~
+There are large amount of data flowing among ONAP components, mostly via DMaaP and Web Services. 
+For example, all events/feed collected by DCAE collectors go through DMaaP. 
+DMaaP is backed by Kafka, which is a system for Publish-Subscribe, 
+where data is not meant to be permanent and gets deleted after certain retention period. 
+Kafka is not a database, means that data there is not for query.
+Though some components may store processed result into their local databases, most of the raw data will eventually lost. 
+We should provide a systematic way to store these raw data, and even the processed result,
+which will serve as the source for data analytics and machine learning, providing insight to the network operation.
+
+
+Relations with Other ONAP Components
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The architecture below depicts the DataLake MS as a part of ONAP. Only the relevant interactions and components are shown.
+
+.. image:: ./arch.PNG
+
+Note that not all data storage systems in the picture are supported. In R6, the following storage are supported:
+  - MongoDB
+  - Couchbase
+  - Elasticsearch and Kibana
+  - HDFS
+Depending on demands, new systems may be added to the supported list. In the following we use the term database for the storage, 
+even though HDFS is a file system (but with simple settings, it can be treats as a database, e.g. Hive.)
+
+Note that once the data is stored in databases, other ONAP components and systems will directly query data from the databases, 
+without interacting with DataLake Handler.
+
+Description
+~~~~~~~~~~~
+DataLate Handler's main function is to monitor and persist data flow through DMaaP. The databases are outside of ONAP scope, 
+since the data is expected to be huge, and a database may be a complicated cluster consisting of thousand of nodes.
+
+Admin UI
+~~~~~~~~
+A system administrator uses DataLake Admin UI to:
+  - Configure external database connections, such as host, port, login.
+  - Configure which Topics to monitor, which databases to store the data for each Topic.
+  - Pre-configured 3rd Party Tools dashboards and templates.
+
+This UI tool is used to manage all the Dayalake settings stored in MariaDB. Here is the database schema:
+
+.. image:: ./dbschema.PNG
+
+Feeder
+~~~~~~
+Architecture
+.. image:: ./feeder-arch.PNG
+
+Features
+
+   - Read data directly from Kafka for performance.
+   - Support for pluggable databases. To add a new database, we only need to implement its corrosponding service.
+   - Support REST API for inter-component communications. Besides managing DatAlake settings in MariaDB, 
+   Admin UI also use this API to start/stop Feeder, query Feeder status and statistics.
+   - Use MariaDB to store settings.
+   - Support data processing features. Before persisting data, data can be massaged in Feeder. 
+   Currently two features are implemented: Correlate Cleared Message (in org.onap.datalake.feeder.service.db.ElasticsearchService) 
+   and Flatten JSON Array (org.onap.datalake.feeder.service.StoreService).    
+   - Connection to Kafka and DBs are secured
+
+
+Links
+~~~~~
+   - DataLake Development Environment Setup https://wiki.onap.org/display/DW/DataLake+Development+Environment+Setup
+   - Source Code https://gerrit.onap.org/r/gitweb?p=dcaegen2/services.git;a=tree;f=components/datalake-handler;hb=HEAD