A company creates a new non-production application that runs on an Amazon EC2 instance.

Amazon RDS controls network-level access through security groups, which act as virtual firewalls. To allow an EC2 instance to connect to an RDS database using JDBC, the RDS security group must explicitly allow inbound traffic from the EC2 instance or its associated security group on the appropriate database port.

IAM roles do not control network connectivity to RDS databases. The ec2_authorized_hosts parameter does not exist for RDS engines. The Amazon RDS Data API is not supported for standard JDBC connections and is only available for Aurora Serverless v1 and v2.

Updating the RDS security group is the correct and simplest approach. By adding an inbound rule that allows traffic from the EC2 instance’s security group, the application can securely connect to the database without additional configuration or restarts.

Therefore, Option C is the correct solution.