Rebalances the distribution of Elastic Compute Service (ECS) instances across zones. If ECS instances are unevenly distributed across multiple zones, you can call the RebalanceInstances operation to rebalance the distribution of the ECS instances across the zones.
Operation description
Usage notes
Auto Scaling creates new ECS instances to replace the existing ECS instances to fulfill the rebalancing purpose. Auto Scaling starts the new ECS instances before stopping the existing ECS instances. The rebalancing operation does not affect the performance or service availability of your application.
-
This operation is supported by only multi-zone scaling groups whose
MultiAZPolicyis set toBALANCE. -
A rebalancing operation is required only when the distribution of the instances of a multi-zone scaling group is significantly unbalanced. In a rebalancing activity, Auto Scaling replaces up to 20 ECS instances to rectify the unbalanced distribution.
-
During the execution of a rebalancing operation, if the number of instances in the scaling group approaches or hits the value of MaxSize but the rebalancing operation needs to continue, Auto Scaling allows the total number of ECS instances to momentarily exceed the value of MaxSize by 10%. This temporary surplus condition persists for a duration until equilibrium in the distribution of ECS instances is achieved. Typically, it takes 1 to 6 minutes.
**
Note If the 10% increment of the maximum number of instances in a scaling group yield a non-integer value, the decimal portion is always rounded up to ensure an additional instance is accounted for. For example, you have a scaling group that holds a maximum of 15 ECS instances. During a rebalancing operation, Auto Scaling would permit the total number of instances to momentarily surpass this limit by 2, instead of the calculated 10% (which is 1.5).
Debugging
Authorization information
The following table shows the authorization information corresponding to the API. The authorization information can be used in the Action policy element to grant a RAM user or RAM role the permissions to call this API operation. Description:
- Operation: the value that you can use in the Action element to specify the operation on a resource.
- Access level: the access level of each operation. The levels are read, write, and list.
- Resource type: the type of the resource on which you can authorize the RAM user or the RAM role to perform the operation. Take note of the following items:
- The required resource types are displayed in bold characters.
- If the permissions cannot be granted at the resource level,
All Resourcesis used in the Resource type column of the operation.
- Condition Key: the condition key that is defined by the cloud service.
- Associated operation: other operations that the RAM user or the RAM role must have permissions to perform to complete the operation. To complete the operation, the RAM user or the RAM role must have the permissions to perform the associated operations.
| Operation | Access level | Resource type | Condition key | Associated operation |
|---|---|---|---|---|
| ess:RebalanceInstances | update |
|
| none |
Request parameters
| Parameter | Type | Required | Description | Example |
|---|---|---|---|---|
| ScalingGroupId | string | Yes | The ID of the scaling group. | asg-bp18p2yfxow2dloq**** |
| RegionId | string | No | The region ID of the scaling group. | cn-hangzhou |
Response parameters
Examples
Sample success responses
JSONformat
{
"ScalingActivityId": "asa-kjgffgdfadah****",
"RequestId": "473469C7-AA6F-4DC5-B3DB-A3DC0DE3****"
}Error codes
For a list of error codes, visit the Service error codes.
Change history
| Change time | Summary of changes | Operation |
|---|