A company wants to enforce stricter tagging to track Amazon EC2 and Amazon RDS costs. A SysOps administrator needs to find all resources that violate the required tagging policy. What is the MOST operationally efficient way to detect resources that are missing the mandated tags?

The most operationally efficient way to detect resources missing mandated tags is to enable the AWS Config managed rule required-tags. This rule is specifically designed to evaluate whether your AWS resources have the tags you specify. It's a pre-built solution that requires minimal setup and maintenance, making it highly efficient. Creating an AWS Config rule that invokes a custom Lambda function is a valid approach for more complex tagging policies but is less efficient for a straightforward "required tags" check than using the managed rule. EventBridge rules are good for reacting to events, but for continuous compliance checking across existing and new resources, AWS Config is the dedicated service. Using a managed rule with EventBridge is not a standard or efficient way to enforce tagging policies across all resources.