AWS Certified Solutions Architect - Professional 2020

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Step scaling policy and Cool down period

I thought that step scaling does not have a cooling down period but warm up instead. However on AWS I read:

Cooldown Period:

The cooldown period is the amount of time, in seconds, after a scaling activity completes where previous trigger-related scaling activities can influence future scaling events.

While the cooldown period is in effect, capacity added by the initiating scale-out event is calculated as part of the desired capacity for the next scale-out event. The intention is to continuously (but not excessively) scale out. For example, when an alarm triggers a step scaling policy to increase the capacity by 2, the scaling activity completes successfully and a cooldown period starts. If the alarm triggers again during the cooldown period but at a more aggressive step adjustment of 3, the previous increase of 2 is considered part of the current capacity. Therefore, only 1 is added to the capacity.

For scale in policies, the cooldown period is used to block subsequent scale in events until it has expired. The intention is to scale in conservatively to protect your application’s availability. However, if another alarm triggers a scale-out policy during the cooldown period after a scale in event, Application Auto Scaling scales out your scalable target immediately.

Also see challenge 2 answer F of chapter Architect to Scale which was incorrect which looks like the above example.

1 Answers

Hi Jeroen,

What you’re referring to us Application Auto Scaling which is different than EC2 Auto Scaling which is discussed in the slides and referenced in the lecture and challenge question.   (See

Application Auto-Scaling is a fairly new feature that tries to offer more flexibility and features than the traditional EC2 autoscaling.  It is confusing but do beware of this prior to declaring something incorrect.  I will be adding some material to cover Application Auto-Scaling to the course soon.


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