The amount of time, in seconds, after a scaling activity completes where previous trigger-related scaling activities can influence future scaling events.
For scale out policies, while Cooldown is in effect, the capacity that has been added by the previous scale out event that initiated the Cooldown is calculated as part of the desired capacity for the next scale out. The intention is to continuously (but not excessively) scale out. For example, an alarm triggers a step scaling policy to scale out an Amazon ECS service by 2 tasks, the scaling activity completes successfully, and a Cooldown period of 5 minutes starts. During the Cooldown period, if the alarm triggers the same policy again but at a more aggressive step adjustment to scale out the service by 3 tasks, the 2 tasks that were added in the previous scale out event are considered part of that capacity and only 1 additional task is added to the desired count.
For scale in policies, the Cooldown period is used to block subsequent scale in requests 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, Application Auto Scaling scales out your scalable target immediately.