This solution correctly addresses all requirements with the least operational effort. AWS Glue is a fully managed ETL service, which significantly reduces operational overhead compared to managing an Amazon EMR cluster. Creating a separate Glue job for each customer ensures logical separation. The requirement to encrypt data where it is processed and before storing it in Amazon S3 points to a client-side encryption strategy. Using client-side encryption with AWS KMS managed keys (CSE-KMS) allows the Glue job (the "client") to encrypt data using customer-specific KMS keys before writing the data to S3, fulfilling the encryption and key management requirements with minimal operational burden.

A: Server-side encryption with S3-managed keys (SSE-S3) does not use customer-specific keys, failing a key requirement.

B: Amazon EMR requires more operational effort than AWS Glue. Furthermore, using a custom client-side root key (CSE-Custom) adds significant key management overhead.

D: Amazon EMR has higher operational overhead than AWS Glue. Also, server-side encryption (SSE-KMS) encrypts data upon arrival at S3, not necessarily during processing on the cluster itself.

1. AWS Glue Developer Guide - Security configurations on the AWS Glue console: "You can use security configurations to encrypt your data at rest... When you specify a security configuration for an AWS Glue job

you can specify a KMS key to encrypt at-rest data that is written to local disks by ETL jobs when spilling data." This supports encrypting data "where it is processed".

2. Amazon S3 User Guide - Protecting data using client-side encryption: "Client-side encryption is the act of encrypting your data locally... The AWS Encryption SDK supports client-side encryption with AWS KMS." This document explains that the application (in this case

the AWS Glue job script) performs encryption before upload

which aligns with the CSE-KMS strategy.

3. AWS Glue FAQs: "AWS Glue is a fully-managed ETL service that makes it simple and cost-effective to categorize your data... You don’t need to create and manage the infrastructure." This confirms that AWS Glue is the choice for the least operational effort compared to Amazon EMR.