How big is the risk when updating the Kafka version?

The Amazon MSK version upgrade feature is based on Kafka best practices and uses a rolling update process that allows Kafka to remain available for cluster IO. We recommend that customers follow best practices for ensuring high availability (see https://docs.aws.amazon.com/msk/latest/developerguide/bestpractices.html#ensure-high-availability) and to first perform a Kafka upgrade in a staging environment to test for client compatibility during and post upgrade.