Using Amazon CloudWatch alarms - Amazon CloudWatch
Common features of CloudWatch alarms

Using Amazon CloudWatch alarms

You can create alarms that watch metrics and send notifications or automatically make changes to the resources you are monitoring when a threshold is breached. For example, you can monitor the 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 under-used instances to save money.

You can create both metric and composite alarms in Amazon CloudWatch.

You can create alarms on Metrics Insights queries that use AWS resource tags to filter and group metrics. To use tags with alarms, on the https://console.aws.amazon.com/connect/, choose Settings. On the CloudWatch Settings page, under Enable resource tags on telemetry, choose Enable. For context-aware monitoring that automatically adapts to your tagging strategy, create alarms on Metrics Insights queries using AWS resource tags. This allows you to monitor all resources tagged with specific applications or environments.

  • A metric alarm watches a single CloudWatch metric or the result of a math expression based on CloudWatch metrics. The alarm performs one or more actions based on the value of the metric or expression relative to a threshold over a number of time periods. The action can be sending a notification to an Amazon SNS topic, performing an Amazon EC2 action or an Amazon EC2 Auto Scaling action, starting an investigation in CloudWatch investigations operational investigations, or creating an OpsItem or incident in Systems Manager.

  • A composite alarm includes a rule expression that takes into account the alarm states of other alarms that you have created. The composite alarm goes into ALARM state only if all conditions of the rule are met. The alarms specified in a composite alarm's rule expression can include metric alarms and other composite alarms.

    Using composite alarms can reduce alarm noise. You can create multiple metric alarms, and also create a composite alarm and set up alerts only for the composite alarm. For example, a composite might go into ALARM state only when all of the underlying metric alarms are in ALARM state.

    Composite alarms can send Amazon SNS notifications when they change state, and can create investigations, Systems Manager OpsItems, or incidents when they go into ALARM state, but can't perform EC2 actions or Auto Scaling actions.

Note

You can create as many alarms as you want in your AWS account.

You can add alarms to dashboards, so you can monitor and receive alerts about your AWS resources and applications across multiple regions. After you add an alarm to a dashboard, the alarm turns gray when it's in the INSUFFICIENT_DATA state and red when it's in the ALARM state. The alarm is shown with no color when it's in the OK state.

You also can favorite recently visited alarms from the Favorites and recents option in the CloudWatch console navigation pane. The Favorites and recents option has columns for your favorited alarms and recently visited alarms.

An alarm invokes actions only when the alarm changes state. The exception is for alarms with Auto Scaling actions. For Auto Scaling actions, the alarm continues to invoke the action once per minute that the alarm remains in the new state.

An alarm can watch a metric in the same account. If you have enabled cross-account functionality in your CloudWatch console, you can also create alarms that watch metrics in other AWS accounts. Creating cross-account composite alarms is not supported. Creating cross-account alarms that use math expressions is supported, except that the ANOMALY_DETECTION_BAND, INSIGHT_RULE, and SERVICE_QUOTA functions are not supported for cross-account alarms.

Note

CloudWatch doesn't test or validate the actions that you specify, nor does it detect any Amazon EC2 Auto Scaling or Amazon SNS errors resulting from an attempt to invoke nonexistent actions. Make sure that your alarm actions exist.

Common features of CloudWatch alarms

The following features apply to all CloudWatch alarms:

  • There is no limit to the number of alarms that you can create. To create or update an alarm, you use the CloudWatch console, the PutMetricAlarm API action, or the put-metric-alarm command in the AWS CLI.

  • Alarm names must contain only UTF-8 characters, and can't contain ASCII control characters

  • You can list any or all of the currently configured alarms, and list any alarms in a particular state by using the CloudWatch console, the DescribeAlarms API action, or the describe-alarms command in the AWS CLI.

  • You can disable and enable alarm actions by using the DisableAlarmActions and EnableAlarmActions API actions, or the disable-alarm-actions and enable-alarm-actions commands in the AWS CLI.

  • You can test an alarm by setting it to any state using the SetAlarmState API action or the set-alarm-state command in the AWS CLI. This temporary state change lasts only until the next alarm comparison occurs.

  • You can create an alarm for a custom metric before you've created that custom metric. For the alarm to be valid, you must include all of the dimensions for the custom metric in addition to the metric namespace and metric name in the alarm definition. To do this, you can use the PutMetricAlarm API action, or the put-metric-alarm command in the AWS CLI.

  • You can view an alarm's history using the CloudWatch console, the DescribeAlarmHistory API action, or the describe-alarm-history command in the AWS CLI. CloudWatch preserves alarm history for 30 days. Each state transition is marked with a unique timestamp. In rare cases, your history might show more than one notification for a state change. The timestamp enables you to confirm unique state changes.

  • You can favorite alarms from the Favorites and recents option in the CloudWatch console navigation pane by hovering over the alarm that you want to favorite and choosing the star symbol next to it.

  • Alarms have an evaluation period quota. The evaluation period is calculated by multiplying the alarm period by the number of evaluation periods used.

    • The maximum evaluation period is seven days for alarms with a period of at least one hour (3600 seconds).

    • The maximum evaluation period is one day for alarms with a shorter period.

    • The maximum evaluation period is one day for alarms that use the custom Lambda data source.

Note

Some AWS resources don't send metric data to CloudWatch under certain conditions.

For example, Amazon EBS might not send metric data for an available volume that is not attached to an Amazon EC2 instance, because there is no metric activity to be monitored for that volume. If you have an alarm set for such a metric, you might notice its state change to INSUFFICIENT_DATA. This might indicate that your resource is inactive, and might not necessarily mean that there is a problem. You can specify how each alarm treats missing data. For more information, see Configuring how CloudWatch alarms treat missing data.