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Master‐slave configuration is a model where one centralized device known as the master controls one or more devices known as slaves. In a master‐slave configuration a replica set constitutes a master node and several slave nodes. Once the relationship between master and slave is established, the flow of control is only from master to the slaves. In master‐slave replication, all the incoming data are written on the master node, and the same data is replicated over several slave nodes. All the write requests are handled by the master node, and the data update, insert, or delete occurs in the master node, while the read requests are handled by slave nodes. This architecture supports intensive read requests as the increasing demands can be handled by appending additional slave nodes. If a master node fails, write requests cannot be fulfilled until the master node is resumed or a new master node is created from one of the slave nodes. Figure 2.9 shows data replication in a master‐slave configuration.