Which solution will meet these requirements?

Explanations:

While using EC2 instances in an Auto Scaling group behind an Application Load Balancer is a good approach for scaling the application, deploying Amazon Redshift does not provide a MySQL-compatible solution. Redshift is a data warehouse and is not suitable for OLTP (online transaction processing) workloads, which MySQL typically handles.

This option proposes using EC2 instances in a target group behind an Application Load Balancer, which is good for application scalability. However, creating an Amazon RDS for MySQL cluster does not provide automatic scaling; it provides high availability with Multi-AZ deployments but does not automatically scale in response to traffic.

This option effectively combines the scalability of EC2 instances in an Auto Scaling group with an Application Load Balancer to handle increased traffic, and Amazon Aurora Serverless for MySQL provides a highly available and automatically scaling database solution. Aurora Serverless can scale automatically based on the application’s demand.

While using EC2 instances behind an Application Load Balancer is valid for scalability, Amazon ElastiCache for Redis is primarily used for caching and does not replace the MySQL database. This solution does not address the need for a highly available and automatically scalable database layer, which is critical for handling increased traffic.