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amazon-web-servicesamazon-cloudwatchamazon-cloudwatchlogsamazon-cloudwatch-metrics

Math Expression on AWS Cloudwatch metrics is not giving expected output

I have created two metrics (m1 and m2) on my logs which will give me sum of some filter pattern, I wanted to add math expression in metric to sum these two metrics so I have added SUM([m1,m2]) but it is not giving me actual sum, Please refer below snapshot.

Snapshot of metrics and expression

I tried to add expressions as m1+m2 but still no luck. One thing I tried, m1 + 2 is giving me exact sum as 5. Not sure if anything is missing here.

Update (2019-07-18):

Adding stacked snapshot,

Stacked Image

Solution

  • The SUM() functions sums up values per datapoint. On your last datapoints you have the value 2 for Completed and no value for Failed, so the sum is 2 + 0 = 2. Number widget on the other hand displays the last value returned which for Failed count is 3, but that 3 didn't happen at the last observed time period, it happened before.

    You can do few thing here:

    • Update the metric filter on the logs to emit the value 0 as default if no Failed events are encountered.
    • Add a new expression to your graph, FILL(m1, 0), with ID e3 for example, which will give you a continuous line with zeros when there are no failures and the number of failures otherwise. Then you can update your SUM expression to be SUM([m2, e3]).

    You can do this on both or your metrics, so you don't have gaps in any of them. This will make the graphing and alarming more consistent and intuitive.