A financial company recently added more features to its mobile app. The new features required the company to create a new topic in an existing Amazon Managed Streaming for Apache Kafka (Amazon MSK) cluster. A few days after the company added the new topic, Amazon CloudWatch raised an alarm on the RootDiskUsed metric for the MSK cluster. How should the company address the CloudWatch alarm?

RootDiskUsed signals that the EBS storage attached to the brokers is nearing capacity. Amazon MSK supports increasing broker storage and enabling automatic volume expansion; doing so relieves the pressure without changing instance type or ZooKeeper nodes.

B. ZooKeeper metadata is tiny; its storage is not tracked by the RootDiskUsed metric on brokers.
C. Larger instances add CPU/RAM but do not increase attached storage, so RootDiskUsed remains high.
D. Target-Volume-in-GiB is a per-topic retention setting, not a storage-expansion mechanism for broker disks.

1. Amazon MSK Developer Guide – “Expanding storage” (“Increase the EBS storage attached to each broker or enable automatic storage scaling”) (https://docs.aws.amazon.com/msk/latest/developerguide/volume-expansion.html).

2. Amazon MSK Metrics – “RootDiskUsed” description (tracks broker EBS utilization) (https://docs.aws.amazon.com/msk/latest/developerguide/monitoring.html#broker-metrics).