A company runs an application on a group of Amazon Linux EC2 instances and must retain all application log files for 7 years for compliance. A reporting tool must be able to access all log files concurrently. Which storage solution meets these requirements MOST cost-effectively?

Amazon S3 is the most cost-effective solution for long-term, highly durable storage of application log files. It offers virtually unlimited scalability and robust data durability (11 nines), making it ideal for compliance requirements like 7-year retention. S3 also provides various storage classes (e.g., S3 Glacier Deep Archive) for further cost optimization based on access patterns, and reporting tools can easily access objects concurrently via the S3 API. Amazon EBS is block storage attached to a single EC2 instance, making it unsuitable for concurrent access from multiple instances and less cost-effective for long-term archival. Amazon EFS is a scalable file system accessible by multiple EC2 instances, but it is generally more expensive than S3 for archival storage and may not be the most cost-effective for infrequently accessed log files. Amazon EC2 instance store provides temporary block-level storage tied to the life of the instance, making it unsuitable for durable, long-term retention.