Which solution will meet these requirements MOST cost-effectively?

Explanations:

While using UltraWarm nodes can help reduce costs, transitioning all input data to S3 Glacier Deep Archive immediately may not align with compliance requirements, as the data is needed for 1 month in the OpenSearch cluster before deletion. Additionally, replacing all data nodes with UltraWarm nodes may not provide sufficient performance for the read-only analysis during that month.

This option reduces costs by decreasing the number of data nodes and using UltraWarm nodes to handle the expected capacity. Transitioning input data to S3 Glacier Deep Archive after 1 month using an S3 Lifecycle policy ensures compliance with data retention requirements, as the data remains accessible during the analysis period.

Although this option incorporates cold storage nodes for further cost savings, it complicates the architecture unnecessarily. Transitioning indexes from UltraWarm to cold storage may not be needed for the given scenario. Additionally, deleting the input data from S3 after 1 month conflicts with the requirement to retain a copy of all input data.

While reducing data nodes and using instance-backed data nodes can manage costs, transitioning input data to S3 Glacier Deep Archive immediately might not comply with data retention policies. The data needs to remain available for analysis for one month before deletion, making this option less suitable.