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I have an alarm setup in AWS cloudwatch which generates a data point every hour. When its value is greater than or equal to 1, it goes to ALARM state. Following are the settings

enter image description here

On 2nd Nov, it got into ALARM state and then back to OK state in 3 hours. I'm just trying to understand why it took 3 hours to get back to the OK state instead of 1 hour because the metric run every hour.

Here's are the logs which prove that metric transited from ALARM to OK state in 3 hours.

enter image description here

Following is the graph which shows the data point value every hour.

enter image description here

Lokesh
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1 Answers1

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This is probably because alarms are evaluated on longer period then your 1 hour. The period is evaluation range. In your case, the evaluation range could be longer then your 1 hour, thus it takes longer for it to change.

There is also thread about this behavior with extra info on AWS forum:

. Unexplainable delay between Alarm data breach and Alarm state change

jmrah
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Marcin
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  • The evaluation period is set to 1 in my case (see additional configuration in my first screenshot). Therefore it can't be longer than 1 hour. – Lokesh Nov 06 '20 at 11:02
  • @Lokesh evaluation period and evaluation range are different. You have no control over the range. – Marcin Nov 06 '20 at 11:06
  • Since I have no control, do you know what's its value? – Lokesh Nov 06 '20 at 11:13
  • @Lokesh I don't know this time. But in the forum thread, they write that it depends on your period. So if your evaluation period is 1h, evaluation range would be more. They write "CloudWatch attempts to retrieve a higher number of data points than specified by Evaluation Periods". – Marcin Nov 06 '20 at 11:19
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    ok. That explains the 3 hour delay in raising the alarm. Thank you – Lokesh Nov 06 '20 at 11:21