Replication is one of the most important factors in achieving reliability for Kafka systems. Replicas of message logs for each topic partition are maintained across different servers in a Kafka cluster. This can be configured for each topic separately. What it essentially means is that for one topic, you can have the replication factor as 3 and for another, you can use 5. All the reads and writes happen through the leader; if the leader fails, one of the followers will be elected as leader.
Generally, followers keep a copy of the leader's log, which means that the leader does not make the message as committed until it receives acknowledgment from all the followers. There are different ways that the log replication algorithm has been implemented; it should ensure that, if leader tells the producer that the message is committed, it must be available...
