Set the cooldown period

What is the cooldown period?

The cooldown period helps you prevent a scaling group from launching or terminating additional KEC instances before the previous activity takes effect.

When you manually scale in or scale out a scaling group or Auto Scaling replaces unhealthy KEC instances, Auto Scaling does not need to wait for the cooldown period to complete by default.

Why is the cooldown period required?

A KEC instance takes a period of time to help reduce load after the KEC instance is added to a scaling group. Without the cooldown period, Auto Scaling continually triggers a scaling activity before the load drops. When the load is distributed to the newly added KEC instances, the system scales in due to the reduced load.

Example

When the business load surges, an alarm associated with scaling policies is triggered. When the alarm is triggered, Auto Scaling launches a KEC instance to help deal with the increasing business load. The KEC instance takes several minutes to start and gradually receives requests from the SLB instance. During this period, the alarm may be triggered again. Without the cooldown period, Auto Scaling launches an additional KEC instance whenever the alarm is triggered.

If the cooldown period is set, Auto Scaling suspends all the simple scaling policies or manual scaling activities until the cooldown period ends. The default cooldown period is 120 seconds. Thus, the newly added KEC instance has time to deal with application traffic.

After the cooldown period ends, all the suspended scaling activities are resumed. If the alarm is triggered again, Auto Scaling launches another KEC instance and the cooldown period takes effect again. However, if the newly added KEC instance can help lower the CPU usage of all KEC instances in the scaling group to the normal level, Auto Scaling maintains the current size of the scaling group.

Set the cooldown period

The default cooldown period is 120 seconds.

To adjust the cooldown period, perform the following steps:

1. Go to the details page of a scaling group.

2. Click the Alarm-Triggered Policy tab.

3. Find the target alarm-triggered policy and click Modify in the Operation column.

4. In the dialog box that appears, specify the cooldown period within the range of 120 to 99999 seconds.

5. Click OK.