Based on this information, what should the developer use to auto scale based on concurrent users?
An Amazon SNS topic to be invoked when a concurrent user threshold is met
An Amazon Cloudwatch NetworkIn metric
Amazon CloudFront to leverage AWS edge locations
A custom Amazon CloudWatch metric for concurrent users
Explanations:
Amazon SNS is used for sending notifications, not for auto scaling. It cannot directly scale based on concurrent users.
The NetworkIn metric measures the amount of incoming network traffic, not concurrent users, so it is not suitable for auto scaling based on users.
Amazon CloudFront helps with content delivery and caching at edge locations. It is not directly related to scaling based on concurrent users.
A custom Amazon CloudWatch metric can be created to track concurrent users. This allows the application to auto scale based on real-time user count.