Drivers upload delivery confirmation (signature photos) via FTP from handhelds to a single EC2 instance. Each device writes files into user-specific directories; the EC2 instance queries a central DB to add metadata, then archives the file to S3. As volume grows, the FTP server on the EC2 instance is dropping connections and failing; a cron reboot was used as a temporary workaround. Devices cannot be changed. Design a scalable solution that guarantees files reach the archive and that backend systems are updated.

The correct solution leverages AWS Transfer Family for a scalable, managed FTP service that directly writes files to S3. This eliminates the single point of failure and scalability issues of the EC2 FTP server. S3 event notifications (via SNS) trigger a Lambda function to process the files, add metadata, and update backend systems, ensuring guaranteed delivery and processing without modifying the handheld devices. Incorrect options: An Auto Scaling group with an ALB would distribute FTP traffic, but FTP is stateful and difficult to load balance effectively without sticky sessions, which can still lead to issues. It also doesn't address the underlying processing logic. Using EFS with AWS Transfer Family would provide a scalable FTP front-end, but EFS is a file system, not an object store, and still requires an EC2 instance to process files, reintroducing a potential bottleneck and complexity. Updating handheld devices is explicitly ruled out by the problem statement ("Devices cannot be changed").