Which service should a solutions architect recommend?

Explanations:

Amazon Aurora MySQL is a managed database service that provides high availability and scalability. However, it is not serverless, meaning that it requires selecting a specific instance type and managing capacity, which does not align with the requirement for anticipating more users in the future without upfront instance type selection.

Amazon Aurora Serverless for MySQL allows for automatic scaling of the database based on demand, which fits well with the infrequent access patterns and minimal downtime requirement. It can automatically adjust capacity to accommodate varying workloads, making it ideal for situations where usage patterns are unpredictable.

Amazon Redshift Spectrum is designed for running complex queries on large datasets stored in Amazon S3. It is not a direct replacement for a transactional database like MySQL and is not suitable for the sales team’s needs, as it is more focused on analytics rather than OLTP (Online Transaction Processing).

Amazon RDS for MySQL is a managed relational database service that requires selecting an instance type. Although it provides automated backups and maintenance, it does not have the same level of scaling flexibility as Aurora Serverless, which makes it less suitable for the needs of the sales team who may anticipate future growth without specific capacity planning.