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In a Kafka cluster, one of the brokers serves as the controller, which is responsible for managing the states of partitions and replicas and for performing administrative tasks like reassigning partitions. The following describes the states of partitions and replicas, and the kind of operations going through the controller.


Valid states are:


  • NewPartition: After creation, the partition is in the NewPartition state. In this state, the partition should have replicas assigned to it, but no leader/isr yet.

  • OnlinePartition: Once a leader is elected for a partition, it is in the OnlinePartition state.
  • OfflinePartition: If, after successful leader election, the leader for partition dies, then the partition moves to the OfflinePartition state.