Manage and Operate Auto Scaling – Scaling Group

A scaling group is a group of Elastic Compute Service () instances or elastic container instances that can be used for similar business scenarios. If you have multiple business scenarios, you can create multiple scaling groups. Auto Scaling automatically adjusts the number of instances in the scaling groups based on your configurations to meet your business requirements.

Scaling Groups

A scaling group is a key component of Auto Scaling. After you configure an Elastic Compute Service (ECS) template for a scaling group and enable the scaling group, Auto Scaling can automatically scale ECS instances in the scaling group based on a scaling rule. You can also manually add existing ECS instances to the scaling group.

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Scaling rule

Auto Scaling scales ECS instances in a scaling group based on a scaling rule and the maximum or minimum number of ECS instances specified for the scaling group. Assume that a scaling group can have up to 45 ECS instances. If you configure a scaling rule to increase the number of ECS instances in the scaling group to 50, Auto Scaling only increases the number of ECS instances to 45 at most.

Scaling activity

  • Only one scaling activity can be executed at a time in a scaling group.
  • An ongoing scaling activity cannot be terminated. For example, if a scaling activity is being executed to create 20 ECS instances but only five have been created, you cannot forcibly terminate the scaling activity.
  • If an ECS instance failed to be added or removed in a scaling activity, the system preserves the transactional integrity of each ECS instance instead of the whole scaling activity. That is, the system rolls back the ECS instance that failed to be added or removed, but not the scaling activity. For example, if 20 ECS instances are created for a scaling group but only 19 ECS instances are added to the back-end server group of a Server () instance, only the ECS instance that failed to be added is released.
  • Auto Scaling uses a Resource Access Management (RAM) role to call the ECS API to create ECS instances. Therefore, the system charges you for the ECS instances that are rolled back until they are released.

Cooldown time

  • During the cooldown time, the system rejects all scaling activities triggered by tasks toward a scaling group. However, when you manually execute a scaling rule or a scheduled task starts at the scheduled time, the system can trigger a scaling activity immediately without waiting for the cooldown time to expire.
  • The cooldown time starts after the last ECS instance is added to or removed from the scaling group in a scaling activity.

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