Amazon CloudWatch
User Guide

Create or Edit a CloudWatch Alarm

You can choose specific metrics to trigger the alarm and specify thresholds for those metrics. You can then set your alarm to change state when a metric exceeds a threshold that you have defined.

To create an alarm

  1. Open the CloudWatch console at

  2. In the navigation pane, choose Alarms, Create Alarm.

  3. For the Select Metric step, do the following:

    1. Choose a metric category (for example, EC2 Metrics).

    2. Select an instance and metric (for example, CPUUtilization).

    3. For the statistic, choose one of the statistics (for example, Average) or predefined percentiles, or specify a custom percentile (for example, p95.45).

    4. Choose a period (for example, 1 Hour).

    5. Choose Next.

  4. For the Define Alarm step, do the following:

    1. Under Alarm Threshold, type a unique name for the alarm and a description of the alarm. The alarm name must contain only ASCII characters. For Whenever, specify a threshold (for example, 80 percent of CPU utilization) and the number of datapoints ("M" out of "N") that must be breaching to trigger the alarm. For more information, see Evaluating an Alarm.

    2. Under Additional settings, for Treat missing data as, choose how to have the alarm treat missing data points. For more information, see Configuring How CloudWatch Alarms Treat Missing Data.

      If the alarm uses a percentile as the monitored statistic, choose whether to evaluate or ignore cases with low sample rates. If you choose ignore, the current alarm state is maintained when the sample size is too low. For more information, see Percentile-Based CloudWatch Alarms and Low Data Samples.

                Treat missing data and Percentiles with low samples UI fields
    3. Under Actions, select the type of action to have the alarm to perform when the alarm is triggered.

    4. Choose Create Alarm.

You can also add alarms to a dashboard. For more information, see Add or Remove an Alarm from a CloudWatch Dashboard.

To edit an alarm

  1. Open the CloudWatch console at

  2. In the navigation pane, choose Alarms.

  3. Select the alarm, and then choose Actions, Modify.

  4. In the Modify Alarm dialog box, update the alarm as necessary and choose Save Changes.

    You cannot change the name of an existing alarm. You can change the description. Or you can copy the alarm, and give the new alarm a different name. To copy an alarm, select the alarm and then choose Actions, Copy.

To update an email notification list that was created using the Amazon SNS console

  1. Open the Amazon SNS console at

  2. In the navigation pane, choose Topics, and then select the ARN for your notification list (topic).

  3. Do one of the following:

    • To add an email address, choose Create subscription. For Protocol, choose Email. For Endpoint, type the email address of the new recipient. Choose Create subscription.

    • To remove an email address, choose the Subscription ID. Choose Other subscription actions, Delete subscriptions.

  4. Choose Publish to topic.