Kafka min.insync.replicas validation gap at topic creation

Configuration boundary

The min.insync.replicas setting determines the minimum in-sync replicas required for acks=all writes. Local single-broker clusters typically use default.replication.factor=1 and min.insync.replicas=1, ensuring all writes succeed. Production environments often configure broker defaults with min.insync.replicas=2 or higher for durability guarantees.

Runtime failure mode

When a topic is created with replication factor 1 but inherits or overrides min.insync.replicas=2, producers using acks=all encounter NOT_ENOUGH_REPLICAS errors at runtime. Kafka currently permits this configuration mismatch at topic creation time rather than rejecting it during validation.

Questions

1. Should topic creation validate that min.insync.replicas does not exceed the topic's replication factor, or is the current runtime failure behavior intentional?
2. How should operators audit and reconcile broker defaults with topic-level overrides following a KRaft migration?