A company is migrating a legacy application from an on-premises data center to AWS.

A is the correct answer because it uses Amazon DocumentDB (with MongoDB compatibility) as a key-value database that can scale based on demand and supports encryption in transit and at rest. Amazon DocumentDB is a fully managed document database service that is designed to be compatible with the MongoDB API. It is a NoSQL database that is optimized for storing, indexing, and querying JSON data. Amazon DocumentDB supports encryption in transit using TLS and encryption at rest using AWS Key Management Service (AWS KMS). Amazon DocumentDB also supports provisioned IOPS volumes that can scale up to 64 TiB of storage and 256,000 IOPS per cluster. To connect to Amazon DocumentDB, you can use the instance endpoint, which connects to a specific instance in the cluster, or the cluster endpoint, which connects to the primary instance or one of the replicas in the cluster. Using the cluster endpoint is recommended for high availability and load balancing purposes. References:

https://docs.aws.amazon.com/documentdb/latest/developerguide/what-is.html

https://docs.aws.amazon.com/documentdb/latest/developerguide/security.encryption.html

https://docs.aws.amazon.com/documentdb/latest/developerguide/limits.html

https://docs.aws.amazon.com/documentdb/latest/developerguide/connecting.html