When using imported key material with AWS KMS, you maintain control over the key lifecycle. AWS KMS allows you to import new key material into an existing KMS key (of type "external" or "imported"), thus rotating the key material without changing the key ID or ARNs. This enables applications to continue using the same key for cryptographic operations without disruption.
You can also set an expiration time for the old key material, after which AWS KMS deletes the old material and requires new key material to be imported, enforcing regular rotation per your compliance requirements.
AWS Documentation Extract:
"To rotate imported key material, you can re-import new key material into the same KMS key. This retains the same key ID and ARNs so applications are unaffected. You can set an expiration time for imported key material and replace it as needed, ensuring compliance with your rotation policy." (Source: AWS Key Management Service Developer Guide, Importing Key Material, Rotating Key Material) Other options:
A: You cannot create a new KMS key with the same key ID as an existing one.
B: Deleting and recreating the key disrupts application access because the key ID changes.
D: Automatic rotation is only available for AWS-managed keys, not for imported key material.
Reference: AWS Certified Solutions Architect - Official Study Guide, KMS and Key Rotation Section.

The most efficient way for management-style reporting is AWS Cost Explorer, because it is designed for interactive cost analysis, filtering, grouping, and exporting reports without building a data pipeline. If the organization has activated cost allocation capabilities (for example, by tagging resources or using other allocation methods), Cost Explorer can present costs in a way that supports chargeback/showback and budgeting. From an operational standpoint, generating and downloading a report from Cost Explorer is quick, requires minimal setup, and is repeatable for periodic budget planning.
Option A (Athena) is powerful but typically requires setting up the Cost and Usage Report (CUR) delivery to Amazon S3, defining schemas, and writing/maintaining SQL queries. That is more operational overhead than needed when the ask is "most efficient way to obtain this report information." Option C (billing dashboard bill download) provides invoice-style line items, but it is not optimized for slicing/grouping "by user" and may not align with departmental budgeting workflows. Option D is unrelated: AWS Budgets alerts on thresholds and forecasts; it does not generate a billed-items-by-user report.
Important nuance: "by user" reporting in AWS is usually achieved through cost allocation tags, account structure, or other allocation dimensions rather than literal per-person IAM identity billing. In practice, departments/teams/users are mapped via tagging and chargeback structures, which Cost Explorer is intended to analyze and export. As a result, Cost Explorer is the most operationally efficient tool to produce a downloadable report for budget planning.
Therefore, B best meets the requirement with the least effort and fastest path to a usable report.

* Amazon FSx for Lustre: Lustre is a high-performance file system designed for workloads that require fast storage with sustained high throughput and low latency. It integrates with Amazon S3, making it suitable for HPC environments.
* Persistent File Systems:
* Persistent Storage: Suitable for long-term storage and recurrent use, providing durability and availability.
* High Throughput and Low Latency: Persistent Lustre file systems can handle large amounts of data with sub-millisecond latency, meeting the needs of high-performance computing workloads.
* Simultaneous Access: FSx for Lustre allows thousands of compute instances to access and process large datasets concurrently, ensuring that the high volume of data is handled efficiently.
* Highly Available: FSx for Lustre is designed to provide high availability and is managed by AWS, reducing the operational burden.
References:
* Amazon FSx for Lustre
* High-Performance Computing on AWS

The key requirement is to meet an RTO of less than 4 hours while using as few resources as possible during normal operations. A backup-and-restore style DR approach using AMIs in a secondary Region aligns with that goal, and AWS CloudFormation is the most operationally efficient way to automate rebuilding the environment. AWS disaster recovery guidance describes backup-and-restore as the lowest-cost pattern during steady state because compute resources are not running in the recovery Region until needed. CloudFormation is preferable to custom scripts because it gives repeatable infrastructure deployment with less custom operational code. Keeping instances active in another Region or AZ would consume more resources during normal operations than necessary.