• Auto Scaling

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  5. Basic Concepts
  6. Scaling Actions

Scaling Actions

A scaling action adds instances to or removes instances from an AS group. It ensures that the number of instances in the application system is the same as the number of expected instances.

A scaling action is triggered when the number of instances in an AS group is not the same as the expected number. This occurs when the condition specified by an AS policy is met or after you manually change the expected number of instances.

  • When the condition specified by an AS policy is met, AS changes the expected number of instances according to the value or percentage specified in the AS policy. In this case, the expected number of instances is inconsistent with the actual number, triggering a scaling action.
  • After you manually change the expected number of instances, it becomes inconsistent with the actual number of instances in the AS group, and a scaling action is triggered.

The following describes the expected number of instances (Expected Instances) and its related concepts.

  • Expected Instances is the expected number of instances in an AS group.
  • Min. Instances or Max. Instances are the minimum or maximum number of instances in an AS group.

    The expected number of instances must fall between the minimum and maximum.

  • Cooldown Period starts after each scaling action is complete. During the cooldown period, scaling actions triggered by alarms will be denied. Scheduled and periodic scaling actions are not restricted.

For details, see section Scaling Actions.