The "min.insync.replicas" configuration specifies the minimum number of insync replicas required for a partition to accept messages from the producer. If the insync replica count of a partition falls under the specified "min.insync.replicas", then the broker will reject messages for producers using acks=all. These producers will suffer unavailability as they will see a NotEnoughReplicas or NotEnoughReplicasAfterAppend exception.
We currently have an UnderMinIsrPartitionCount metric which is useful for identifying when partitions fall under "min.insync.replicas", however it is still difficult to identify which topic partitions are affected and need fixing.
We can leverage the describe topics command in TopicCommand to add an option "--under-minisr-partitions" to list out exactly which topic partitions are below "min.insync.replicas".