A finance company hosts a data lake in Amazon S3. Each night several third parties upload financial data over SFTP. The company currently runs its own SFTP server on an EC2 instance in a public subnet; a cron job on that instance moves uploaded files into the data lake. The SFTP server is reachable at sftp.example.com via Amazon Route 53. How should a solutions architect improve the reliability and scalability of this SFTP solution?

Migrating to AWS Transfer for SFTP directly addresses the reliability and scalability concerns. AWS Transfer for SFTP is a fully managed service that provides highly available and scalable SFTP endpoints, eliminating the operational overhead of managing EC2 instances, Auto Scaling groups, and load balancers. It integrates directly with S3, simplifying the data ingestion process into the data lake. Moving the EC2 instance into an Auto Scaling group behind an ALB would improve scalability and some reliability, but ALBs do not support the SFTP protocol. Placing the EC2 instance behind an NLB would support SFTP, but still requires managing the underlying EC2 instances and does not offer the fully managed benefits of AWS Transfer for SFTP. Migrating to a file gateway using AWS Storage Gateway is not suitable as it's designed for on-premises applications to access cloud storage, not for external SFTP uploads.