You can enable a scaling group so that, if the existing number of ECS instances is less than the MinSize value of an enabled (Active) scaling group, Auto Scaling creates Pay-As-You-Go ECS instances until the MinSize value is reached.
For example, if MinSize is set to 5 during the creation of a scaling group, and the group has only 2 ECS instances when enabled, Auto Scaling creates 3 ECS instances to add to the group.
You can only enable inactive scaling groups with active scaling configurations.
A single scaling group can have one active scaling configuration at a time.
On the Scaling group management page, click Enable next to the scaling group to be enabled.