Metric-based Auto scaling policies in Amazon EC2

Question

I have defined the following policies on t2.micro instance:

Take action A whenever {maximum} of CPU Utilization is >= 80% for at least 2 consecutive period(s) of 1 minute.

Take action B whenever {Minimum} of CPU Utilization is <= 20% for at least 2 consecutive period(s) of 1 minute.

Is my interpretation is wrong that: if the min (max) of CPU drops below (goes beyond) 20 (80) for 2 minutes, these rules have to be activated?

Because my collected stats show for example the Max of cpu has reached 90% twice in two consecutive period of 1 minute, but I got No Alarm!

Cheers

Answer 1

It seems my interpretation is not correct! The policy works based on the Average of the metric for every minute! It means the first policy will be triggered if the AVERAGE of stat Datapoints within a minute is >= 80% for two consecutive periods of 1 minute. The reason is simple: Cloudwatch does not consider stat datapoints less than 1 Min granularity. So if I go for 5 Minutes period, Max and Min show the correct behavior.