Merge pull request cfpb#1163 from nickgrippin/cluster-docs

Cluster docs updated

Author: jmarin

Documents/cluster.md

@@ -3,4 +3,28 @@
 ## Cluster Management
 
 The project uses the [Akka Cluster HTTP Management](http://developer.lightbend.com/docs/akka-management/current/cluster-http-management.html) module to report on cluster member status as well as to perform cluster
-management tasks. Please refer to the documentation of this module for cluster management tasks (i.e. downing a node from the cluster)
+management tasks. Please refer to the documentation of this module for cluster management tasks (i.e. downing a node from the cluster)
+
+## Roles
+
+There are four different cluster roles, each managed within the cluster project.
+
+### API
+
+The API cluster role is responsible for the four different APIs: Admin, Public, Filing, and the TCP Panel Loader
+
+### Persistence
+
+The persistence cluster role contains actors responsible for tracking and persisting information about submissions, institutions, and LAR validation
+
+### Query
+
+This cluster role contains actors responsible for projecting data to a read-only database (currently Cassandra)
+
+### Publication
+
+The publication role is responsible for generating publication artifacts based on HMDA data (i.e. A&D reports, Modified LAR, etc.)
+
+## Running cluster roles
+
+The configuration setting `"akka.cluster.roles"` in `cluster/src/main/resources/application.conf` defines which cluster roles will start when the HMDA Platform starts.  By default, all four roles are set to start at the same time, but this can be changed to any single role or combination of roles.  Setting the `HMDA_CLUSTER_ROLES` environment variable will allow you to decide which roles to spin up.

README.md

@@ -32,6 +32,10 @@ Module responsible for validating incoming data by executing validation rules as
 
 Module responsible for persisting information into the system. It becomes the system of record for HMDA data
 
+### Cluster
+
+Module responsible for managing the various cluster roles, as well as starting the Hmda Platform
+
 ### API
 
 This module contains both public APIs for HMDA data for general use by third party clients and web applications, as well as endpoints for receiving data and providing information about the filing process for Financial Institutions