An Internet-of-Things (IoT) solutions company wants to migrate its on-premises infrastructure into the AWS Cloud. The data engineering team is looking for a fully managed NoSQL persistent data store with in-memory caching to maintain low latency which is critical for real-time data processing. The team is well versed with the access patterns for the underlying database and expects the number of concurrent users to touch up to a million so the database should be able to scale elastically. Which of the following AWS services would you recommend for this use-case?