Which AWS service provides automatic scaling and high availability for NoSQL databases?

Amazon Keyspaces is the correct choice because it is a fully managed, serverless, and highly available NoSQL database service that is compatible with Apache Cassandra. This service automatically scales based on the application demand, which is crucial for handling variable workloads typically associated with NoSQL databases. Keyspaces abstracts the complexities of infrastructure management, allowing customers to focus on application development instead of database management.

In contrast, Amazon EC2 is a compute service that requires users to manage the underlying infrastructure, which does not directly provide database functionalities like automatic scaling for NoSQL databases. AWS Lambda, while a powerful serverless compute service that can be used in conjunction with various databases, does not serve as a database itself, so it lacks the built-in features associated with NoSQL data storage and retrieval. Amazon RDS, on the other hand, is designed for relational databases and provides managed services, but it does not specifically cater to the unique requirements of NoSQL databases like Keyspaces does, particularly in terms of scaling and high availability tailored for NoSQL use cases.