title: Bus and REST services with fast response for decoupling?
body: <p>Having several backend modules exposing a REST API, one of the module needs to call other modules through their API and have an immediate response. </p>
  
  <p>A solution is to directly call the REST API from this 'top' module. The problem is that it creates coupling, does not support scaling or failover natively.</p>
  
  <p>A kind of bus (JMS, ESB) permits to decouple the modules by avoiding the need of endpoints known by the modules. They only 'talk' to the bus.</p>
  
  <p>What would you use to enable fast response through the bus (another constraint is you don't have multicast as it could be deployed in the cloud)?</p>
  
  <p>Also is it reasonable to still rely on the REST api or would a JMS listener be better?
  I thought about JMS, Camel, ESB's. Do you know about companies using such architecture?</p>
  
  <p><em>ps: a module could be a java war running on a tomcat instance for example.</em></p>