Which of the following services would you use to implement real-time data stream processing?

Amazon Kinesis Data Analytics is designed specifically for real-time data stream processing. This service allows users to analyze streaming data using standard SQL queries. It can take in large volumes of data from various sources, providing the ability to continuously process and analyze this data for insights in real-time.

Kinesis Data Analytics enables real-time data analysis, making it ideal for scenarios such as monitoring applications, financial transactions, or social media feeds. By integrating with other AWS services, it can easily fetch data from sources like Kinesis Data Streams or Amazon Kinesis Data Firehose, process it on the fly, and deliver structured outputs to dashboards or other AWS services.

While AWS Lambda is also a tool that supports event-driven architectures and can process data in real-time, it is not fundamentally designed for stream processing in the way that Kinesis Data Analytics is. Amazon S3 is primarily a storage solution and does not provide real-time processing capabilities on its own. Amazon RDS, a managed relational database service, is used for structured data storage and retrieval but does not support real-time data stream processing. Therefore, for the requirement of implementing real-time data stream processing, Amazon Kinesis Data Analytics is the most suitable choice.