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If step scaling policies are too involved for your taste, you can instead use target tracking policies. All you do is select a metric and target value, and Auto Scaling will create a CloudWatch Alarm and a scaling policy to adjust the number of instances to keep the metric near that target.

The metric you choose must change proportionally to the instance load. Metrics like this include average CPU utilization for the group and request count per target. Aggregate metrics like the total request count for the ALB don't change proportionally to the load on an individual instance and aren't appropriate for use in a target tracking policy.

In addition to scaling out, target tracking will scale in by deleting instances to maintain the target metric value. If you don't want this behavior, you can disable scaling in. Also, just as with a step scaling policy, you can optionally specify a warm‐up time.