An ecommerce company stores about 300 MB of JSON analytics data per month. The company needs a disaster recovery solution that keeps the data accessible in milliseconds if required and retains the data for 30 days. Which option is the MOST cost-effective solution?

Amazon S3 Standard is the most cost-effective solution for this scenario. It offers high durability, availability, and low-latency access (milliseconds) suitable for active data, and its pricing for 300 MB of data is very low. The 30-day retention requirement is easily met. Amazon OpenSearch Service (formerly Amazon Elasticsearch Service) is designed for search and analytics, not primarily for cost-effective storage of raw JSON files with simple retrieval needs. It would be significantly more expensive for just storing and retrieving data. Amazon S3 Glacier is a very low-cost archival storage service, but it's designed for infrequent access, and retrieval times can range from minutes to hours, not milliseconds. This doesn't meet the accessibility requirement. Amazon RDS for PostgreSQL is a relational database service. While it could store JSON data, it's overkill and far more expensive for simply storing 300 MB of files and retrieving them. It's designed for structured data and complex querying, not object storage.