A scaling cooldown helps you prevent your Auto Scaling group from launching or terminating additional instances before the effects of previous activities are visible.
When you use simple scaling, after the Auto Scaling group scales using a simple scaling policy, it waits for a cooldown period to complete before any further scaling activities due to simple scaling policies can start.
Scaling-specific cooldown period
In addition to specifying the default cooldown period for your Auto Scaling group, you can create cooldowns that apply to a specific simple scaling policy.
A scaling-specific cooldown period overrides the default cooldown period.
One common use for a scaling-specific cooldown period is with a scale-in policy.
Because this policy terminates instances, EC2 Auto Scaling needs less time to determine whether to terminate additional instances.
Terminating instances should be a much quicker operation than launching instances.
The default cooldown period of 300 seconds is therefore too long.