Explanation: Amazon CloudWatch alarms watch a single metric over a time period that the user specifies and performs one or more actions based on the value of the metric relative to a given threshold over a number of time periods. The alarm has three states: Alarm, OK and Insufficient data. The Alarm will change to Insufficient Data when any of the three situations arise: when the alarm has just started, when the metric is not available or when enough data is not available for the metric to determine the alarm state. If the user wants to find that RDS is not available, he can setup to receive the notification when the state is in Insufficient data.