CloudWatch Concepts

Metrics

• Metrics are the fundamental concept in CloudWatch.

• A metric represents a time-ordered set of data points that are published to CloudWatch.

• Think of a metric as a variable to monitor, and the data points as representing the values of that variable over time.

  • For example, the CPU usage of a particular EC2 instance is one metric provided by EC2.

• By default, many AWS services provide free metrics for resources (such as Amazon EC2 instances, Amazon EBS volumes, and Amazon RDS DB instances).

• For a charge, you can also enable detailed monitoring for some resources.

• For custom metrics, you can add the data points in any order, and at any rate you choose.

• Metrics exist only in the Region in which they are created.

• Each data point in a metric has a time stamp, and (optionally) a unit of measure.

Dimensions

• A dimension is a name/value pair that is part of the identity of a metric.

• You can assign up to 10 dimensions to a metric.

• Think of dimensions as categories for those metrics.

Namespaces

• A namespace is a container for CloudWatch metrics.

• Metrics in different namespaces are isolated from each other, so that metrics from different applications are not mistakenly aggregated into the same statistics.

• There is no default namespace.

  • You must specify a namespace for each data point you publish to CloudWatch.

Resolution

• Standard resolution = one-minute granularity.

• High resolution = granularity of one second.

• EC2 Basic monitoring = Metrics every 5 minutes.

• EC2 Detailed monitoring = Metrics every minute; it is a paid option.

Custom Metrics

• You can define custom metrics for your own use.

• Once Amazon CloudWatch contains your custom metrics, you can view those in the CloudWatch console.

• Uses API called PutMetricData.

CloudWatch Alarms

• You can use an alarm to automatically initiate actions on your behalf.

• An alarm watches a single metric over a specified time period, and performs one or more specified actions, based on the value of the metric relative to a threshold over time.

• The action is a notification sent to an Amazon SNS topic or an Auto Scaling policy.

• When creating an alarm, select an alarm monitoring period that is greater than or equal to the metric's resolution.

  • For example, basic monitoring for EC2 is metrics every 5 minutes.

    • So, when setting an alarm, select a period greater than 5 minutes.

• An alarm can be in three possible states:

  • OK - The metric or expression is within the defined threshold.

  • ALARM - The metric or expression is outside of the defined threshold.

  • INSUFFICIENT_DATA - The alarm has just started, the metric is not available, or not enough data is available for the metric to determine the alarm state.