In a cluster, partitions are distributed across nodes where each server share the responsibility of request processing for individual partitions. Even partitions are replicated across several nodes configured in a Kafka environment.  This is the reason why Kafka is the system. The system or node which act as a primary server for each partition is termed as a leader while other systems where data gets replicated is called a follower. It is a leader's responsibility to read or write data on given partitions but followers system passively replicates data of leader’s system. In case of failure of the leader system, any of the follower systems becomes a leader. Now we can understand cluster environment architecture where each system playing the role of leader for some of the partitions while other system playing as a follower and making Kafka popular as a fault-tolerant system. This is the reason why Kafka has taken a centre stage in-stream messaging platforms.