Amazon CloudWatch monitors your Amazon Web Services (AWS) resources and the applications you run on AWS in real time. You can use CloudWatch to collect and monitor metrics, which are the variables you can measure to evaluate your resources and applications.
You can create alarms that observe metrics and send notifications or automatically make changes to the features you’re monitoring when a limit is breached. For example, you can monitor CPU usage and disk reads and writes of your Amazon EC2 instances, and then use that data to determine whether you should launch additional instances to handle increased load. You can also use this data to stop underutilized instances to save money.
With CloudWatch, you gain system-wide visibility into resource utilization, application performance, and operational health.
References: