A legacy workload has the stateless application tier on a single large EC2 instance launched from an AMI, and the MySQL database on a single EC2 instance. CPU on the app server often hits 100%, causing outages. Patching is applied manually and has caused downtime. The company needs to make the application highly available with the least development effort. Which solution meets this requirement?

The correct solution provides high availability with minimal development effort. Creating a new AMI with SSM Agent allows for automated patching and management. Using an Auto Scaling group with smaller instances behind an Application Load Balancer addresses the CPU bottleneck and provides horizontal scaling and high availability for the stateless application tier. Migrating the database to Amazon Aurora MySQL offers a highly available, fault-tolerant, and scalable managed database service that is MySQL-compatible, requiring minimal application changes. Refactoring to Lambda or containerizing with ECS would require significant development effort. Changing to a smaller Graviton instance without an Auto Scaling group doesn't solve high availability or scaling. Migrating to DocumentDB, DynamoDB, or Neptune would require significant database refactoring due to schema and query language differences.