By using replicated configuration with two master servers (a primary and a secondary), the secondary master server can take over processing even if there is a failure in the primary master server. By registering JobTracker (MapReduce) that makes up Hadoop as a cluster application, the secondary master server can take over processing if an error occurs in Hadoop.
Furthermore, you can also have redundancy in the transmission route between the master server and the slave server. Replicating by using two transmission networks means that the route where a failure occurs can be isolated so that network communications can continue.
Point
A Hadoop network can also be made up of one master server or one transmission network.
However, it is recommended to use a replicated master server configuration so that operations can continue if there is a failure in the master server, which is the single point of failure for Hadoop, as explained in "1.2.2 High Reliability".
