question

[sudipya]

is this java based messaging application ?

[RawSanj]

Yes. This is a simple chat application focused mainly to demonstrate scaling chat application to multiple instances.

The idea was not to create a full-fledge chat app but to showcase the use of Redis Pub/Sub and WebSockets to sync messages between different instances.

WebSockets are stateful i.e. a client application (Web/Js app in this case) connects and maintains connection to a single instance of the JVM Server. So users connected to one JVM instance could only see messages sent to that instance only.
This would put a limit to maximum number of Users to connect and text.
To overcome this, Redis Pub/Sub is used to sync (send/receive) messages from one JVM instance to all other instances.

As and when time permits, I'd be enhancing this to have User authentication and other features. Feel free to fork and contribute.