Amazon Athena is a serverless, interactive query service designed to analyze data directly in Amazon S3 using standard SQL. For this scenario, the developer can define a table schema over the CSV files in the S3 bucket and run SQL queries to generate the summary report. Since Athena is serverless, there is no infrastructure to provision or manage, such as clusters or virtual machines. This approach directly meets the requirement for the least amount of operational overhead, as the developer only needs to write and run the query.

A. Amazon S3 Select is incorrect because it is used to retrieve a subset of data from a single S3 object, not to perform aggregate queries across multiple files.
C. Amazon Redshift is a data warehouse service. Using it would require provisioning a cluster and creating a process to load the data from S3, which is significant operational overhead.
D. Amazon EC2 would require the developer to provision a virtual server, install query software, manage the operating system, and handle data transfer, representing the highest operational overhead. ---

1. Amazon Athena Documentation: "What is Amazon Athena?" - "Amazon Athena is an interactive query service that makes it easy to analyze data directly in Amazon Simple Storage Service (Amazon S3) using standard SQL... Athena is serverless

so there is no infrastructure to set up or manage

and you pay only for the queries that you run."

Source: AWS Documentation

Amazon Athena User Guide.

2. Amazon S3 Select Documentation: "Filtering and retrieving data using S3 Select" - "Amazon S3 Select is an Amazon S3 feature that makes it easy to retrieve specific data from the contents of an object using simple SQL expressions without having to retrieve the entire object."

Source: AWS Documentation

Amazon S3 User Guide.

3. Amazon Redshift Documentation: "Overview of Amazon Redshift" - "An Amazon Redshift data warehouse is a collection of computing resources called nodes

which are organized into a group called a cluster. To use Amazon Redshift

you launch a set of nodes

called an Amazon Redshift cluster."

Source: AWS Documentation

Amazon Redshift Database Developer Guide.

4. Amazon EC2 Documentation: "What is Amazon EC2?" - "Amazon Elastic Compute Cloud (Amazon EC2) provides scalable computing capacity in the Amazon Web Services (AWS) Cloud. Using Amazon EC2 eliminates your need to invest in hardware up front... You are responsible for OS-level maintenance such as patching."

Source: AWS Documentation

Amazon EC2 User Guide for Linux Instances.