An application on EC2 instances requires dynamic feature flags shared across applications. The app must poll at intervals for updated flag values and cache the values when retrieved. Which solution provides the most operationally efficient implementation?

AWS AppConfig is purpose-built for managing application configurations, including feature flags. It allows for controlled deployments, rollbacks, and validation of configurations. The AWS AppConfig Agent runs locally on the EC2 instance, polls AppConfig for updates, and exposes the configuration via a localhost endpoint. This design is operationally efficient because the application reads from a local endpoint, reducing network latency and offloading polling logic. Storing flags in AWS Secrets Manager is not ideal as it's designed for sensitive data, not general application configurations. ElastiCache is a caching layer, not a primary configuration store. DynamoDB with DAX is a powerful combination for high-performance data access but is overkill for simple feature flags and lacks the controlled deployment features of AppConfig. Systems Manager Parameter Store can store configurations, but the application would directly poll the AWS API, which is less efficient than using the AppConfig Agent's local cache and controlled update mechanism.