recovering from broker failures in MSK

Please find answers inline:

Q1: If a broker is being upgraded, Kafka will reassign the leadership of some partitions. After the upgrade will the leaderships get reassigned again so that all brokers are being used as before?

• Upgrades will be in done in a rolling fashion on each broker at a time. So for example in a 3 broker cluster when broker 1 is undergoing upgrade, all the leadership that broker 1 contains will be reassigned to broker 2 and broker 3. When upgrade is complete and all 3 brokers are active, current partition leadership ratio between brokers is validated against a broker config parameter 'leader.imbalance.per.broker.percentage' which by default 10% and accordingly leadership is distributed so all brokers gets leader reassigned again after upgrade.

Q2: If 1 AZ (AZ1) goes down, I understand that Kafka will automatically reassign the partitions to the other brokers in the two AZs without impacting the producers and consumers. When AZ1 comes back will MSK automatically create/restart the failed broker and redistribute the partitions?

• That's correct, once the AZ comes back failed brokers will be relaunched and added to the existing cluster topology and then leader partitions will be distributed automatically