An organization stores very large files in Amazon S3 and is building a web app that displays metadata about those files to users. After a user selects a file based on metadata, the app will allow the file to be downloaded. The metadata index must support single-digit millisecond lookups. Which AWS service should be used to provide that metadata indexing and low-latency retrieval?

Amazon DynamoDB is a fully managed NoSQL database service that provides single-digit millisecond performance at any scale, making it ideal for low-latency metadata lookups. Its flexible schema and key-value store capabilities are well-suited for indexing file metadata. Amazon EC2 provides virtual servers and is not a database service for indexing. AWS Lambda is a serverless compute service, used for running code, not for data storage and retrieval. Amazon RDS is a relational database service, which, while capable of storing metadata, typically has higher latency and overhead compared to DynamoDB for high-performance, key-value lookups, especially at scale.