ROX-16887: always extend SLO calculation over entire 28 days #87
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Extended average over time refers to the time series effectively being extended over the entire time interval. This is in contrast to avg_over_time, which only averages over time intervals where the time series is not nil. This is important during the initial 28 days of Central instances. For example, consider a Central instance that lived for 5 minutes and was down for 2 minutes. Using avg_over_time, the availability would be 3 min / 5 min = 60%. The extended average over 28 days would yield 1 - 2 min / 28 days ~ 99.995%. After the initial 28 days, both averages are equivalent.
0x656b694d
approved these changes
May 5, 2023
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Extended average over time refers to the time series effectively being extended over the entire time interval. This is in contrast to avg_over_time, which only averages over time intervals where the time series is not nil. This is important during the initial 28 days of Central instances. For example, consider a Central instance that lived for 5 minutes and was down for 2 minutes. Using avg_over_time, the availability would be
3 min / 5 min = 60%. The extended average over 28 days would yield1 - 2 min / 28 days = 99.995%. After the initial 28 days, both averages are equivalent, because data points will exist for the entire 28d range.Also make sure that alerts only fire as long as the Central instance still exists (
central:sli:availability >= 0condition).