Kafka: acks=all without min.insync.replicas still loses data

"All" means all in-sync replicas. If only the leader is in sync, all means one.

Code

# Topic config
min.insync.replicas=2
replication.factor=3

Output

With min.insync.replicas=1, acks=all on a degraded partition
acknowledges a write only the dying leader has seen.

With 2, the producer gets NotEnoughReplicasException instead - fail, do not lose.

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Published 2026-08-11