Apache Kafka Practice

The NotEnoughReplicasException error occurs when a producer attempts to send a message to a Kafka topic but the number of in-sync replicas available falls below the configured minimum. In Kafka, a topic partition's availability is managed through replication, where one replica is designated as the leader that handles all writes, while other replicas can serve as followers. Each individual partition has a configured minimum number of in-sync replicas (ISR), and this setting determines how many replicas must acknowledge a message before it is considered successfully produced.

When a producer sends a message, Kafka checks whether the minimum in-sync replicas are available to ensure data durability and fault tolerance. If there are not enough replicas in sync due to failures, network issues, or any other disruptions, the producer will receive a NotEnoughReplicasException, indicating that the message cannot be successfully produced because the required level of redundancy cannot be guaranteed.

This emphasizes the importance of configuring the replication factor and the minimum in-sync replicas appropriately to maintain data integrity in a production environment. The other situations described do not lead to this specific error; for instance, a missing leader would produce a different error, and topics exceeding size limits is unrelated to the replica check.