A company’s online shopping app stores orders on an Amazon RDS for PostgreSQL Single-AZ DB instance. Management wants to remove single points of failure and minimize database downtime without changing the application code. Which solution meets these requirements?

Converting the existing Single-AZ RDS instance to Multi-AZ is the most straightforward solution. This modification creates a synchronous standby replica in a different Availability Zone, providing automatic failover without requiring application code changes. This addresses the single point of failure and minimizes downtime. Creating a new Multi-AZ deployment and restoring from a snapshot would involve more downtime and operational overhead. Creating a read-only replica helps with read scalability and disaster recovery but doesn't provide automatic failover for write operations, which are critical for an online shopping app. Placing RDS in an EC2 Auto Scaling group is not applicable; RDS is a managed service and doesn't run directly on EC2 instances in a way that Auto Scaling groups would manage its high availability.