Basics

Collects and manages operational data
CW consist of 3 parts Metrics, Logs & Events
CW collects some metrics natively i.e. automatically while for some we need to install CW Agent to collect.
CW uses namespaces to seperate out data into logical units
All AWS generated data goes into "AWS/servicename" namespace
CW Metrics are collection of datapoints. Each datapoint consists of a namespace, dimensions, timestamp & value.
Dimensions are name value pair. EC2 Instance id is an example of a dimension
Resolution defines frequency or granularity of datapoints. Standard/Default resolution is 60second
High resolution can be at resolution of 1second
For any resolution less than 60s, data is retained for 3 hours.For 60s data is retained for 15 days.For 300s for 63 days, for 3600s retained for 455 days
Alarms - Watches a metric over a period of time
Alarms can be configured t triger of actions , Actions based on value of metrics i.e. a criteria. Alarm can have in 3 states "OK", "InAlarm", "Insufficient Data"
CW is a public service