What should a solutions architect do to ensure the system can automatically scale for the increased traffic?

Explanations:

Enabling storage Auto Scaling on the RDS instance will allow the database to automatically increase storage as needed, ensuring it does not run out of space as traffic and data increase. This is a suitable approach for handling unpredictable growth in storage requirements.

Migrating to Amazon Aurora could enable storage Auto Scaling, but it would require significant changes to the application to support the new database engine. Since the application uses Oracle-specific PL/SQL functions, this option would not be viable without rewriting the application logic.

Configuring an alarm for low free storage space on the RDS instance would notify the team when storage is low but would not enable automatic scaling of storage. This does not directly address the need for automated scaling to handle increasing demand.

Setting the Auto Scaling group to use average CPU utilization as a scaling metric will enable automatic scaling of EC2 instances based on demand, helping the application to handle the increasing traffic load effectively and avoid overloading instances.

Using free memory as a scaling metric is generally not as effective for scaling the Auto Scaling group because memory utilization can fluctuate independently of traffic and may not accurately reflect CPU load, which is more directly correlated with traffic and demand.