A production VPC has a VPC flow log. The security team supplied a deny-list of IP addresses and wants near-real-time automated notifications if any deny-listed IP accesses the application, to justify adding protections like WAF. The product manager will approve changes only if the security team can demonstrate the issue, and cost must be minimized. Which additional steps meet the requirement most cost-effectively?

The correct solution is the most cost-effective and provides near-real-time notifications. Sending VPC flow logs directly to CloudWatch Logs and then using a CloudWatch metric filter to identify deny-listed IPs is efficient. A CloudWatch alarm triggered by this metric filter, with a short period and low datapoints to alarm, ensures prompt notification via SNS. This approach leverages existing CloudWatch capabilities, minimizing additional service costs. The S3/Athena/QuickSight option is more complex and expensive for simple alerts, as QuickSight is primarily for visualization, not real-time alerting. The S3/OpenSearch/Lambda option introduces significant operational overhead and cost with OpenSearch and Lambda for log processing, which is overkill for this specific alerting requirement. The CloudWatch Logs/Athena connector option is also more complex and costly than necessary, involving Athena queries and S3 event notifications, which are less direct for real-time alerts than CloudWatch Alarms.