Amazon VPC NAT Gateways now support Amazon CloudWatch Monitoring and  Resource Tagging

You can now monitor bytes, packets, active connections and several other metrics for NAT Gateways via CloudWatch console and AWS CLI. You can setup CloudWatch Alarms to notify you of crossing thresholds. All metrics are provided with a 1 min frequency. For more information about the metrics, see  Monitoring Your NAT Gateway with Amazon CloudWatch.
Quelle: aws.amazon.com