Why does AWS Cloudwatch use an Evaluation Range when determining alarm state with missing data points?











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From the docs:




No matter what value you set for how to treat missing data, when an alarm evaluates whether to change state, CloudWatch attempts to retrieve a higher number of data points than specified by Evaluation Periods. The exact number of data points it attempts to retrieve depends on the length of the alarm period and whether it is based on a metric with standard resolution or high resolution. The timeframe of the data points that it attempts to retrieve is the evaluation range.




The docs go on to give an example of an alarm with 'EvaluationPeriods' and 'DatapointsToAlarm' set to 3. They state that Cloudwatch chooses the 5 most recent datapoints. Part of my question is, Where are they getting 5? It's not clear from the docs.



The second part of my question is, why have this behavior at all (or at least, why have it by default)? If I set my evaluation period to 3, my Datapoints to Alarm to 3, and tell Cloudwatch to 'TreatMissingData' as 'breaching,' I'm going to expect 3 periods of missing data to trigger an alarm state. This doesn't necessarily happen, as illustrated by an example in the docs.










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    From the docs:




    No matter what value you set for how to treat missing data, when an alarm evaluates whether to change state, CloudWatch attempts to retrieve a higher number of data points than specified by Evaluation Periods. The exact number of data points it attempts to retrieve depends on the length of the alarm period and whether it is based on a metric with standard resolution or high resolution. The timeframe of the data points that it attempts to retrieve is the evaluation range.




    The docs go on to give an example of an alarm with 'EvaluationPeriods' and 'DatapointsToAlarm' set to 3. They state that Cloudwatch chooses the 5 most recent datapoints. Part of my question is, Where are they getting 5? It's not clear from the docs.



    The second part of my question is, why have this behavior at all (or at least, why have it by default)? If I set my evaluation period to 3, my Datapoints to Alarm to 3, and tell Cloudwatch to 'TreatMissingData' as 'breaching,' I'm going to expect 3 periods of missing data to trigger an alarm state. This doesn't necessarily happen, as illustrated by an example in the docs.










    share|improve this question
























      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite











      From the docs:




      No matter what value you set for how to treat missing data, when an alarm evaluates whether to change state, CloudWatch attempts to retrieve a higher number of data points than specified by Evaluation Periods. The exact number of data points it attempts to retrieve depends on the length of the alarm period and whether it is based on a metric with standard resolution or high resolution. The timeframe of the data points that it attempts to retrieve is the evaluation range.




      The docs go on to give an example of an alarm with 'EvaluationPeriods' and 'DatapointsToAlarm' set to 3. They state that Cloudwatch chooses the 5 most recent datapoints. Part of my question is, Where are they getting 5? It's not clear from the docs.



      The second part of my question is, why have this behavior at all (or at least, why have it by default)? If I set my evaluation period to 3, my Datapoints to Alarm to 3, and tell Cloudwatch to 'TreatMissingData' as 'breaching,' I'm going to expect 3 periods of missing data to trigger an alarm state. This doesn't necessarily happen, as illustrated by an example in the docs.










      share|improve this question













      From the docs:




      No matter what value you set for how to treat missing data, when an alarm evaluates whether to change state, CloudWatch attempts to retrieve a higher number of data points than specified by Evaluation Periods. The exact number of data points it attempts to retrieve depends on the length of the alarm period and whether it is based on a metric with standard resolution or high resolution. The timeframe of the data points that it attempts to retrieve is the evaluation range.




      The docs go on to give an example of an alarm with 'EvaluationPeriods' and 'DatapointsToAlarm' set to 3. They state that Cloudwatch chooses the 5 most recent datapoints. Part of my question is, Where are they getting 5? It's not clear from the docs.



      The second part of my question is, why have this behavior at all (or at least, why have it by default)? If I set my evaluation period to 3, my Datapoints to Alarm to 3, and tell Cloudwatch to 'TreatMissingData' as 'breaching,' I'm going to expect 3 periods of missing data to trigger an alarm state. This doesn't necessarily happen, as illustrated by an example in the docs.







      amazon-web-services amazon-cloudwatch






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      asked Nov 8 at 21:31









      user3658800

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