As implied by its name, the Distributed Replication Service (DRS) is a runtime component in WAS-ND that is used to replicate data among distributed processes in a WAS cell. In WAS-ND V5, DRS can either be used as a failover mechanism for HTTP Session objects, as discussed in Chapter 22, “Session Management,” or to replicate dynacache entries, as described in Chapter 19.
 DRS is sometimes also referred to as WebSphere Internal Messaging.
Before we discuss configuring DRS and topology options, we need to outline the various components that comprise DRS as well as some terms relating to its use.
The first term is replica. A replica is nothing more than an in-memory copy of data. If one server updates ...