CloudWatch is AWS' telemetry hub. Here's the link to the official overview page
My deep dive will focus on important features that are useful for SREs or Ops folks.
By default, AWS CloudWatch shows metrics related to AWS services. You can add custom dashboards on top.
How CloudWatch Works:
AWS Resource metrics + Custom metrics -> CloudWatch -> Stats
CloudWatch metrics are grouped and isolated by namespace. The period for which metrics are retained goes down as resolution or granularity increases. An important concept to learn in CloudWatch is 'Dimensions' - the categorization based on which you can retrieve specific statistics for a particular dimension or set of dimensions.
When defining custom metrics, you need to decide what Unit you want to use. Valid values are:
Seconds | Microseconds | Milliseconds | Bytes | Kilobytes | Megabytes | Gigabytes | Terabytes | Bits | Kilobits | Megabits | Gigabits | Terabits | Percent | Count | Bytes/Second | Kilobytes/Second | Megabytes/Second | Gigabytes/Second | Terabytes/Second | Bits/Second | Kilobits/Second | Megabits/Second | Gigabits/Second | Terabits/Second | Count/Second | None