After terminating EC2 instances, several Elastic IP addresses remain allocated but unassociated. The company wants to automatically release any Elastic IP addresses that are left unattached after instance termination with the LEAST operational effort. Which design best satisfies this requirement?

The correct option leverages AWS Config's eip-attached managed rule, which automatically detects unassociated Elastic IPs. By configuring automatic remediation with the AWS-ReleaseElasticIP Systems Manager Automation runbook, AWS handles the release process with minimal operational effort. This is a native AWS solution designed for this exact scenario. The other options involve custom Lambda functions or complex EventBridge rules. While technically possible, they require more development, testing, and maintenance, increasing operational overhead compared to the managed rule and automation runbook. Using AWS Trusted Advisor as an EventBridge target is incorrect as Trusted Advisor provides recommendations, not real-time events for this purpose. Deleting an EIP via CloudFormation is not a real-time event-driven solution.