Point-to-point (request-response) style will couple client to the server.

Clients with new schema will be able to read records saved with old schema and clients with old schema will be able to read records saved with new schema.

These three metrics are critical for cluster health:
OfflinePartitionsCount: Indicates partitions without active leaders - a sign of broker failure.
ActiveControllerCount: There should be exactly one active controller. A count # 1 signals controller failure.
UncleanLeaderElectionsPerSec: Tracks leader elections where out-of-sync replicas were selected - risky for data loss.
From Kafka Monitoring Documentation:
"Offline partitions and unclean leader elections should trigger alerts. Also, ensure a single active controller is running." A is about topics pending deletion - not critical.
E is a per-topic record metric, not broker-level.
Reference: Kafka Monitoring > Key JMX Metrics

Kafka's new bidirectional client compatibility introduced in 0.10.2 allows this. Read more herehttps://www.confluent.io/blog/upgrading-apache-kafka-clients-just-got-easier/