Recipe: Fault tolerant communication layer using Zookeeper

This recipe caters to the following use case
There are S(Active) + s(standby) sender nodes and R(Active) + r(standby) receiver nodes. The objective is following

• If one of the S Active server goes down a standby node should take up the task.
• If one of the R Active server goes down a standby node should take up the task.
• When there is a change in receiver the Sender must get updated and send the message to correct destination

This also uses recipe described in https://issues.apache.org/jira/browse/ZOOKEEPER-923

This was developed for a different project S4 which is also open sourced http://s4.io/. The communication layer and task management layer is completely independent of S4 and can be used in any application.