Create a metric alarm that uses a wall clock evaluation window

You can create a metric alarm that aligns its evaluation window to wall clock boundaries instead of a sliding window. For information about how wall clock windows work and when to use them, see Wall clock window.

Creating a wall clock alarm using the AWS Management Console

This example shows how to create an alarm that uses a 1-hour wall clock window.

To create a wall clock alarm

1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

2. In the navigation pane, choose Alarms, All alarms.

3. Choose Create alarm.

4. Choose Select metric, choose the metric you want to monitor, and then choose Select metric.

5. Under Metric, for Period, choose a period that supports wall clock windows: 1 minute, 5 minutes, 1 hour, 1 day, or 1 week.

6. Under Conditions, configure the threshold and comparison operator for your alarm.

7. For Evaluation window, choose Wall clock window.

   Note

   If you don't see the Evaluation window option, the metric type or period you selected does not support wall clock windows. Wall clock windows are not available for high-resolution alarms, composite alarms, or PromQL alarms, and are only available for periods of 1 minute, 5 minutes, 1 hour, 1 day, or 1 week.

8. Optionally, choose a time zone for Time zone. The alarm aligns its evaluation window to clock boundaries in this time zone. If you don't choose a time zone, CloudWatch uses UTC. For details about how time zones affect wall clock boundaries, see Time zones and daylight saving time.

9. Configure notifications and actions as needed, then choose Next.

10. Add a name and description for your alarm, then choose Next.

11. Review the alarm configuration and choose Create alarm.

Creating a wall clock alarm (AWS CLI)

Use the PutMetricAlarm API action to create or update a metric alarm with an EvaluationWindow. Set WallClockWindow to align the alarm to wall clock boundaries, or set SlidingWindow to use the default sliding behavior. If you omit the EvaluationWindow parameter, the alarm uses a sliding window.

Example Create an alarm that uses a 1-hour wall clock window

This alarm evaluates the most recently completed clock hour in UTC. To align to a different time zone, set Timezone on the WallClockWindow.

aws cloudwatch put-metric-alarm \
  --alarm-name HourlyCpuAlarm \
  --metric-name CPUUtilization \
  --namespace AWS/EC2 \
  --statistic Average \
  --period 3600 \
  --evaluation-periods 1 \
  --threshold 80 \
  --comparison-operator GreaterThanThreshold \
  --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
  --evaluation-window '{"WallClockWindow":{}}'

Example Create a daily alarm aligned to a specific time zone

This alarm evaluates each calendar day in the America/New_York time zone. Daylight saving time transitions are handled automatically.

aws cloudwatch put-metric-alarm \
  --alarm-name DailyBackupCheck \
  --metric-name SuccessfulBackups \
  --namespace MyApplication \
  --statistic Sum \
  --period 86400 \
  --evaluation-periods 1 \
  --threshold 1 \
  --comparison-operator LessThanThreshold \
  --evaluation-window '{"WallClockWindow":{"Timezone":"America/New_York"}}'

Example Create a weekly alarm in UTC

This alarm evaluates each calendar week (Monday 00:00 UTC through the following Monday 00:00 UTC).

aws cloudwatch put-metric-alarm \
  --alarm-name WeeklyComplianceCheck \
  --metric-name ComplianceFailures \
  --namespace MyApplication \
  --statistic Sum \
  --period 604800 \
  --evaluation-periods 1 \
  --threshold 0 \
  --comparison-operator GreaterThanThreshold \
  --evaluation-window '{"WallClockWindow":{}}'

Example Switch an existing alarm back to a sliding window

Set EvaluationWindow to SlidingWindow to make the change explicit. You can also omit the parameter, which has the same effect.

aws cloudwatch put-metric-alarm \
  --alarm-name HourlyCpuAlarm \
  --metric-name CPUUtilization \
  --namespace AWS/EC2 \
  --statistic Average \
  --period 3600 \
  --evaluation-periods 1 \
  --threshold 80 \
  --comparison-operator GreaterThanThreshold \
  --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
  --evaluation-window '{"SlidingWindow":{}}'

View the evaluation window for an existing alarm

Use the DescribeAlarms API action to retrieve the evaluation window configuration of an alarm. The EvaluationWindow field is included in the response when the alarm uses a wall clock window. If the field is absent, the alarm uses a sliding window.

aws cloudwatch describe-alarms \
  --alarm-names HourlyCpuAlarm

You can also view the evaluation window in the AWS Management Console on the alarm details page.