Per customer business requirements, a system’s high availability is more important than message reliability.

Unclean leader election allows Kafka to elect a non-in-sync replica as a new leader when all in-sync replicas are unavailable. This increases availability at the cost of possible message loss (sacrificing reliability).

From Kafka documentation:

“If unclean.leader.election.enable is set to true, a broker that is not in the ISR can be elected as leader, which increases availability but may lead to data loss.”

A → Correct: Improves availability when ISR is empty.

B → Best practice for quorum-based systems like ZooKeeper but not the setting that trades off reliability.

C → Controls batching latency, unrelated to availability.

D → Retention -1 means “retain forever,” which impacts storage, not HA.

Page Reference:

Kafka: The Definitive Guide, 1st Edition, Chapter 6, p. 195

Apache Kafka Documentation: Topic Config – unclean.leader.election.enable

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