If your AS group supports automatic removal of instances, the instances will be removed based on the configured instance removal policy.

AS supports instance removal policies in the following four methods:

According to earlier created configurations and instances According to the Earlier Created Configurations policy, the instances created earlier will be removed from the AS group preferentially. This policy is useful if you want to update an AS group and phase out instances configured previously.
According to later created configurations and instances According to the Later Created Configurations policy, the instances created later will be removed from the AS group preferentially. This policy is useful if you want to test a new AS configuration item but do not want to reserve it in production.
Earlier created instances: The instances created earlier will be removed from the AS group preferentially. This policy is useful when you upgrade instances in an AS group to a new instance type and phase out old instances and replace them with newer ones.
Later created instances: The instances created later will be removed from the AS group preferentially.

Note: If the instance migration policy is set to Earlier/Later Created Instances, ECSs manually added to the AS group may also be removed. If the instances manually migrated are pay-per-use instances, the Pay-per-use Instance Recycling Mode rule will be followed after the instance is removed. If the manually migrated instances are periodical ones, they will not be deleted or their status will not be changed after the migration. To ensure that the manually migrated instances are not removed, you can enable the protection of the instances on the tab page of AS Group Details > AS Instance.

Auto Scaling

Instance Removal Policy