Amazon ElastiCache for Redis is correct because it provides fully managed in-memory data store services that are compatible with Redis, facilitating real-time data processing due to its high-performance, in-memory capabilities. Amazon RDS is a managed relational database service that provides a variety of database engines but is not primarily memory-based. Amazon S3 is an object storage service and does not offer in-memory data processing. Likewise, Amazon DynamoDB is a managed NoSQL database service which supports in-memory caching but is known for its fast and predictable performance with seamless scalability rather than being primarily memory-based.