The correct answer is: Modify the application to include an expiration timestamp attribute set to 90 days in the future for each new record. Then, configure DynamoDB Time to Live (TTL) to use that attribute for automatic deletion.

DynamoDB TTL is a built-in feature that allows you to automatically delete items after a specified timestamp. By assigning each new item a TTL attribute with a value set to the current time plus 90 days, you ensure that DynamoDB will automatically remove outdated records. This approach reduces storage costs and requires no additional infrastructure or manual intervention, making it the most operationally efficient and cost-effective solution.

Why the other options are incorrect:

Using a CloudFormation stack and redeploying it every 90 days is highly impractical. CloudFormation is designed for provisioning infrastructure, not for managing or rotating data. Recreating stacks would also delete all other resources and create unnecessary complexity and risk.

Using an EC2 instance with a third-party monitoring application introduces ongoing cost, administrative overhead, and custom scripting. It also defeats the goal of minimizing development effort and cost.

Using DynamoDB Streams to trigger a Lambda function that deletes old items is overly complicated and error-prone. Streams only capture changes as they occur and are not designed to track when data becomes outdated. Additionally, scanning for old data in real-time via Lambda would be inefficient and possibly costly.

Why this question matters: This question tests your knowledge of DynamoDB TTL, a feature that is often overlooked but ideal for lifecycle management of temporary or time-bound data. It also reinforces the idea of leveraging managed services for automation to minimize cost and effort.

Tip: When you see requirements around data expiration or retaining records only for a specific number of days, look for TTL features or automated lifecycle policies first. These are the simplest and most efficient tools to use.

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