AWS AmazonCloudWatch documentation change
Summary
Added documentation about sliding/wall-clock evaluation windows and updated multi-day alarm behavior explanation.
Security assessment
Changes describe alarm evaluation mechanics and time window configurations. No evidence of security fixes, vulnerabilities, or security features being documented.
Diff
diff --git a/AmazonCloudWatch/latest/monitoring/alarm-evaluation.md b/AmazonCloudWatch/latest/monitoring/alarm-evaluation.md index 21955a2a1..3ff5ed940 100644 --- a//AmazonCloudWatch/latest/monitoring/alarm-evaluation.md +++ b//AmazonCloudWatch/latest/monitoring/alarm-evaluation.md @@ -67,0 +68,2 @@ If data points are missing soon after you create an alarm, and the metric was be +By default, CloudWatch uses a _sliding window_ for alarm evaluation. Each time the alarm is evaluated, the window advances by one minute, and the boundaries of the window are not aligned to the wall clock. You can instead align the evaluation window to wall clock boundaries and time zones. For more information, see [Alarm evaluation window](./alarm-evaluation-window.html). + @@ -74 +76 @@ If you set an alarm on a high-resolution metric, you can specify a high-resoluti -An alarm is a multi-day alarm if the number of evaluation periods multiplied by the length of each evaluation period exceeds one day. Multi-day alarms are evaluated once per hour. When multi-day alarms are evaluated, CloudWatch takes into account only the metrics up to the current hour at the :00 minute when evaluating. +An alarm is a multi-day alarm if the number of evaluation periods multiplied by the length of each evaluation period exceeds one day. Multi-day alarms are evaluated once per hour. When multi-day alarms are evaluated, CloudWatch takes into account only the metrics up to the current hour at the :00 minute when evaluating. This top-of-the-hour behavior, and the following example, apply to alarms that use a sliding evaluation window, which is the default. @@ -90,0 +93,2 @@ For example, consider an alarm that monitors a job that runs every 3 days at 10: +If the alarm instead uses a wall clock evaluation window, CloudWatch aligns the evaluation window to the wall clock boundary that matches the period in the alarm's selected time zone, rather than clamping to the top of each hour. For example, a multi-day alarm with a one-day period evaluates complete calendar days that end at midnight in the selected time zone, and an alarm with a one-week period evaluates complete calendar weeks. The window advances by one full period when each boundary is reached, so the alarm considers a newly completed calendar period only after that period ends. For more information, see [Alarm evaluation window](./alarm-evaluation-window.html). + @@ -99 +103 @@ Alarm data queries -Configuring how alarms treat missing data +Alarm evaluation window