Amazon CloudWatch is a monitoring service for AWS cloud resources and the applications you run on AWS. You can use Amazon CloudWatch to collect and track metrics, collect and monitor log files, set alarms, and automatically react to changes in your AWS resources. Amazon CloudWatch can monitor AWS resources such as Amazon EC2 instances, Amazon DynamoDB tables, and Amazon RDS DB instances, as well as custom metrics generated by your applications and services, and any log files your applications generate. You can use Amazon CloudWatch to gain system-wide visibility into resource utilization, application performance, and operational health. You can use these insights to react and keep your application running smoothly.

 

-Many metrics are received and aggregated at 1 – minute intervals. Some are at 3 minute or 5 – minute interval

• Metrics data are available for 2 weeks
• Metrics can not be deleted, but they automatically expire after 2 weeks

Metrics Retention

CloudWatch now stores all metrics for 15 months at no extra charge ( nov 2016 ). In order to keep the overall volume of data reasonable, historical data is stored at a lower level of granularity, as follows:

• One minute data points are available for 15 days.
• Five minute data points are available for 63 days.
• One hour data points are available for 455 days (15 months).

CloudWatch metrics require a custom monitoring script to populate the metric:

• Swap Usage
• Available Disk Space

Aggregation : 

• CloudWatch does not aggregate data across regions
• Aggregated statistics are only available when using detailed monitoring.

Cloudwatch

– do not provide detailed monitoring for EMR

• by default detailed monitoring is enable for Auto Scaling

– provide free detailed monitoring for :

• AWS Route 53
• AWS RDS
• AWS ELB
• opsworks

 

• to upload custom metrics you can use the AWS CLI or the API

Reference