The least implementation effort is to publish a custom CloudWatch metric from the existing Lambda function that records the number of orders in each batch, then create a CloudWatch alarm that sends a notification to the SNS topic when the metric value is 0. This avoids building a separate stream-processing pipeline or scheduled analytics job. A new Kinesis consumer and Lambda function would add unnecessary services and operational complexity. A 24-hour scheduled function is also slower than required because the notification must happen as soon as possible. Logging to Kinesis only creates more data movement and still requires separate analysis logic. CloudWatch supports custom metrics, and CloudWatch alarms can send notifications through Amazon SNS when metric thresholds are breached. ( AWS Documentation )

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