What are acks in Kafka producer configuration?

acks controls how many acknowledgements the producer requires from the server before a request is considered complete. acks=0: the producer does not wait for any acknowledgement, delivery is not guaranteed and retries have no effect. acks=1: the leader acknowledges after writing the record to its local log without waiting for the followers, so if the leader fails before the record is replicated, it is lost. acks=all (or -1): the leader waits for all in-sync replicas (ISR) to acknowledge, so the record is not lost as long as at least one in-sync replica stays alive; this is the default and idempotence requires it. The min.insync.replicas setting (default 1) sets how many in-sync replicas, including the leader, must acknowledge when acks=all; if the ISR is smaller, the producer gets a NotEnoughReplicas exception. The choice trades latency against durability.

Expected key concepts: acks, acks=0, acks=1, acks=all, ISR, leader, min.insync.replicas, durability, NotEnoughReplicas, idempotence