Basic Concepts

AS Group

An AS group consists of a collection of ECS instances that apply to the same scenario. It is the basis for enabling or disabling AS policies and performing scaling actions.

AS Configuration

An AS configuration is a template specifying specifications for the ECS instances to be added to an AS group. The specifications include the ECS type, vCPUs, memory, image, login mode, and disk.

AS Policy

AS policies can trigger scaling actions to adjust the number of instances in an AS group. An AS policy defines the conditions for triggering a scaling action and the operation to be performed in a scaling action. When the trigger condition is met, a scaling action is triggered automatically.

Scaling Action

A scaling action adds instances to or removes instances from an AS group. It ensures that the expected number of instances are running in the AS group by adding or removing instances when the triggering condition is met, which improves system stability.

Cooldown Period

To prevent an alarm-based policy from being repeatedly triggered by the same event, you can set a cooldown period. A cooldown period (in seconds) is the period of time between two scaling actions. AS recounts the cooldown period after a scaling action is complete. During the cooldown period, AS denies all scaling requests triggered by alarm-based policies. Scaling requests triggered manually or by scheduled or periodic policies are not affected.

For example, suppose that the cooldown period is set to 300 seconds (5 minutes), and a scheduled policy is specified to trigger a scaling action at 10:32, and a previous scaling action triggered by an alarm policy ends at 10:30. Any alarm-triggered scaling action will then be denied during the cooldown period from 10:30 to 10:35, but the scaling action scheduled for 10:32 will still take place. If the scheduled scaling action ends at 10:36, a new cooldown period starts at 10:36 and ends at 10:41.

Bandwidth Scaling

AS automatically adjusts a bandwidth based on the scaling policies you configured. AS can only adjust bandwidths of EIPs and share bandwidths that are billed on a pay-per-use basis.