Topic replication is very important in Kafka. It is used to construct Kafka deployments to ensure durability and high availability. When one broker fails, topic replicas on other brokers remain available to ensure that data is not lost and Kafka deployment is not disrupted in any case. The replication ensures that the messages published are not lost.
The replication factor specifies the number of copies of a topic kept across the Kafka cluster. It takes place at the partition level and is defined at the subject level. For example, taking a replication factor of two will keep two copies of a topic for each partition. The replication factor cannot be more than the cluster's total number of brokers.
ISR stands for In-Sync Replica, and it is a replica that is up to date with the partition's leader.
