With step scaling policies, you create and manage the CloudWatch alarms that invoke the scaling process. When an alarm is breached, Amazon ECS initiates the scaling policy associated with that alarm. The step scaling policy scales tasks using a set of adjustments, known as step adjustments. The size of the adjustment varies based on the magnitude of the alarm breach.
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If the breach exceeds the first threshold, Amazon ECS applies the first step adjustment.
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If the breach exceeds the second threshold, Amazon ECS applies the second step adjustment, and so on.
We strongly recommend that you use target tracking scaling policies to scale on metrics like average CPU utilization or average request count per target. Metrics that decrease when capacity increases and increase when capacity decreases can be used to proportionally scale out or in the number of tasks using target tracking. This helps ensure that Amazon ECS follows the demand curve for your applications closely.