An application running on EC2 instances in a VPC needs VPC flow logs collected and analyzed, and the company wants the most cost-effective solution. Which approach meets this requirement?

Publishing VPC flow logs to Amazon S3 in Apache Parquet format and using Amazon Athena for analytics is the most cost-effective solution. Parquet is a columnar storage format that is highly optimized for analytical queries, leading to significantly reduced data scanned by Athena and thus lower query costs. Storing data in S3 is also generally more cost-effective for large volumes of log data compared to CloudWatch Logs, especially for long-term retention. Athena is a serverless query service that charges based on data scanned, making it cost-efficient for ad-hoc analysis. Publishing to CloudWatch Logs and using Athena would incur higher storage costs in CloudWatch Logs and potentially higher data transfer costs. Using OpenSearch Service for analytics, while powerful, involves managing a cluster and can be more expensive than Athena for infrequent or ad-hoc queries. Publishing to S3 in text format would be less efficient for Athena queries due to the row-based nature of text files, leading to higher query costs compared to Parquet.