Create a scaling group of the ECS type - Auto Scaling - Alibaba Cloud Documentation Center

A scaling group is a collection of Elastic Compute Service (ECS) instances or elastic container instances that can be used in similar business scenarios. If you want to automatically increase or decrease the number of ECS instances based on fluctuations in your business workloads, you can refer to this topic to create a scaling group of the ECS type.

Procedure

Before you proceed, make sure that you are clear about the method you want to use to create the scaling group, as Alibaba Cloud provides multiple methods to do so. You can refer to the following scenarios to choose a scaling group creation method based on your business requirements:

Scenario 1: You have an existing launch template. In this scenario, you can directly create a scaling group by using the launch template. For more information, see Method 1: Create a scaling group by using a launch template.
Scenario 2: You have an existing ECS instance. In this scenario, you can create a scaling group based on the configurations of the ECS instance. For more information, see Method 2: Create a scaling group based on the configurations of an existing ECS instance.
Scenario 3: You want to configure an instance configuration source only after you create a scaling group. For more information, see Method 3: Create a scaling group from scratch.

Method 1: Create a scaling group by using a launch template

If you want to create a scaling group by using an existing launch template, you can perform the following steps:

Important

Before you proceed, make sure that you have at least one launch template. For information about how to create a launch template, see Create a launch template.

Go to the Create Scaling Group page.
1. Log on to the Auto Scaling console.
  Note
  The first time you log on to Auto Scaling, follow the on-screen instructions to activate Auto Scaling and grant the required permissions. For more information, see Service-linked role.
2. In the top navigation bar, select the region where Auto Scaling is activated.
3. In the left-side navigation pane, click Scaling Groups.
4. On the Scaling Groups page, click Create to go to the Create Scaling Group page.

Click the Create by Form tab and follow the on-screen instructions to create a scaling group.

The following table describes only the required parameters for creating a scaling group by using a launch template. For information about more parameters, see Parameters.

Required parameters

Parameter	Description
Scaling Group Name	Enter a name for the scaling group. The name must meet the requirements displayed on the console.
Type	Specify the type of the scaling group that you want to create. In this example, ECS is used. Note This topic describes only how to create a scaling group of the ECS type. For information about how to create a scaling group of the Elastic Container Instance type, see Create a scaling group of the Elastic Container Instance type.
Instance Configuration Source	Specify an instance configuration source. Auto Scaling creates ECS instances in the scaling group based on the specified source. In this example, Launch Templates is used.
Select Launch Template	Select an existing launch template as prompted. If no existing launch template that meets your requirements exists, you can create a new launch template as prompted.
Select Template Version	Select a version for the launch template based on your business requirements.
Extend Launch Template	You can configure the Extend Launch Template parameter to specify multiple instance types. If you want to specify weights for instance types, see Create a multi-instance type scaling group by using a launch template.
Minimum Number of Instances	Specify the lower limit of the number of ECS instances in the scaling group. If the actual number of ECS instances drops below the lower limit, Auto Scaling triggers a scale-out event to add ECS instances to the scaling group.
Maximum Number of Instances	Specify the upper limit of the number of ECS instances in the scaling group. If the actual number of ECS instances exceeds the upper limit, Auto Scaling triggers a scale-in event to remove excess ECS instances from the scaling group.
Default Cooldown Time (Seconds)	Specify a default cooldown period for the scaling group. Unit: seconds. Default value: 300. For more information, see Cooldown period.
VPC	This parameter is displayed only if you set the Network Type parameter to VPC. After you select a VPC from the VPC drop-down list, all ECS instances in this scaling group reside in the VPC. Warning After you create the scaling group, you cannot change the value of the VPC parameter.
vSwitch	After you select a VPC for the scaling group, you must select one or more vSwitches of the VPC for the scaling group. All ECS instances in the scaling group communicate with each other by using the selected vSwitches. Important We recommend that you select multiple vSwitches. If you select only one vSwitch, scale-out failures caused by insufficient resources in a single zone may often occur. If you select multiple vSwitches, you can set the Scaling Policy parameter to Balanced Distribution Policy to manage the distribution of ECS instances across multiple zones.

Click Create.

Note

After you create the scaling group, you can change the launch template based on your business requirements. For information about how to change a launch template, see Manage launch templates.

Method 2: Create a scaling group based on the configurations of an existing ECS instance

If you want to create a scaling group based on the configurations of an existing ECS instance, you can perform the following steps:

Go to the Create Scaling Group page.
1. Log on to the Auto Scaling console.
  Note
  The first time you log on to Auto Scaling, follow the on-screen instructions to activate Auto Scaling and grant the required permissions. For more information, see Service-linked role.
2. In the top navigation bar, select the region where Auto Scaling is activated.
3. In the left-side navigation pane, click Scaling Groups.
4. On the Scaling Groups page, click Create to go to the Create Scaling Group page.

Click the Create by Form tab and follow the on-screen instructions to create a scaling group.

The following table describes only the required parameters for creating a scaling group based on the configurations of an existing ECS instance. For information about more parameters, see Parameters.

Required parameters

Parameter	Description
Scaling Group Name	Enter a name for the scaling group. The name must meet the requirements displayed on the console.
Type	Specify the type of the scaling group that you want to create. In this example, ECS is used. Note This topic describes only how to create a scaling group of the ECS type. For information about how to create a scaling group of the Elastic Container Instance type, see Create a scaling group of the Elastic Container Instance type.
Instance Configuration Source	Specify an instance configuration source. Auto Scaling creates ECS instances in the scaling group based on the specified source. In this example, Select Existing Instance is used.
Select Existing Instance	Select an existing ECS instance as prompted. After you select an existing ECS instance, Auto Scaling extracts the basic configurations of the ECS instance to create a scaling configuration. Important The basic configurations typically include the instance type, network type, security group, and base image. The instance logon password and instance tags are not extracted.
Minimum Number of Instances	Specify the lower limit of the number of ECS instances in the scaling group. If the actual number of ECS instances drops below the lower limit, Auto Scaling triggers a scale-out event to add ECS instances to the scaling group.
Maximum Number of Instances	Specify the upper limit of the number of ECS instances in the scaling group. If the actual number of ECS instances exceeds the upper limit, Auto Scaling triggers a scale-in event to remove excess ECS instances from the scaling group.
Default Cooldown Time (Seconds)	Specify a default cooldown period for the scaling group. Unit: seconds. Default value: 300. For more information, see Cooldown period.
VPC	This parameter is displayed only if you set the Network Type parameter to VPC. After you select a VPC from the VPC drop-down list, all ECS instances in this scaling group reside in the VPC. Note This parameter is automatically filled based on the VPC of the selected ECS instance. Warning After you create the scaling group, you cannot change the value of the VPC parameter.
vSwitch	After you select a VPC for the scaling group, you must select one or more vSwitches of the VPC for the scaling group. All ECS instances in the scaling group communicate with each other by using the selected vSwitches. Note This parameter is automatically filled based on the vSwitches of the selected ECS instance. You can change the vSwitches or add more vSwitches based on your business requirements. Important We recommend that you select multiple vSwitches. If you select only one vSwitch, scale-out failures caused by insufficient resources in a single zone may often occur. If you select multiple vSwitches, you can set the Scaling Policy parameter to Balanced Distribution Policy to manage the distribution of ECS instances across multiple zones.

Click Create.

Note

If you create a scaling group based on the configurations of an existing ECS instance, a scaling configuration is automatically created. You can Manage scaling configurations based on your business requirements.
If you want the scaling group to provide services immediately, you must enable the scaling group. For more information, see Enable or disable scaling groups.

Method 3: Create a scaling group from scratch

If you want to configure an instance configuration source only after you create a scaling group, perform the following steps:

Go to the Create Scaling Group page.
1. Log on to the Auto Scaling console.
  Note
  The first time you log on to Auto Scaling, follow the on-screen instructions to activate Auto Scaling and grant the required permissions. For more information, see Service-linked role.
2. In the top navigation bar, select the region where Auto Scaling is activated.
3. In the left-side navigation pane, click Scaling Groups.
4. On the Scaling Groups page, click Create to go to the Create Scaling Group page.

Click the Create by Form tab and follow the on-screen instructions to create a scaling group.

The following table describes only the required parameters for creating a scaling group from scratch. For information about more parameters, see Parameters.

Required parameters

Parameter	Description
Scaling Group Name	Enter a name for the scaling group. The name must meet the requirements displayed on the console.
Type	Specify the type of the scaling group that you want to create. In this example, ECS is used. Note This topic describes only how to create a scaling group of the ECS type. For information about how to create a scaling group of the Elastic Container Instance type, see Create a scaling group of the Elastic Container Instance type.
Instance Configuration Source	Specify an instance configuration source. Auto Scaling creates ECS instances in the scaling group based on the specified source. In this example, Create from Scratch is used. Therefore, you can specify an instance configuration source after you create the scaling group. For more information, see Overview.
Minimum Number of Instances	Specify the lower limit of the number of ECS instances in the scaling group. If the actual number of ECS instances drops below the lower limit, Auto Scaling triggers a scale-out event to add ECS instances to the scaling group.
Maximum Number of Instances	Specify the upper limit of the number of ECS instances in the scaling group. If the actual number of ECS instances exceeds the upper limit, Auto Scaling triggers a scale-in event to remove excess ECS instances from the scaling group.
Default Cooldown Time (Seconds)	Specify a default cooldown period for the scaling group. Unit: seconds. Default value: 300. For more information, see Cooldown period.
VPC	This parameter is displayed only if you set the Network Type parameter to VPC. After you select a VPC from the VPC drop-down list, all ECS instances in this scaling group reside in the VPC. Warning After you create the scaling group, you cannot change the value of the VPC parameter.
vSwitch	After you select a VPC for the scaling group, you must select one or more vSwitches of the VPC for the scaling group. All ECS instances in the scaling group communicate with each other by using the selected vSwitches. Important We recommend that you select multiple vSwitches. If you select only one vSwitch, scale-out failures caused by insufficient resources in a single zone may often occur. If you select multiple vSwitches, you can set the Scaling Policy parameter to Balanced Distribution Policy to manage the distribution of ECS instances across multiple zones.

Click Create.

Note

After you create the scaling group from scratch, you can follow the on-screen instructions to immediately create a scaling configuration. You can also create a scaling configuration subsequently, or specify a launch template for the scaling group. For more information, see Manage launch templates and Create a scaling configuration of the ECS type.

Parameters

Basic parameters for creating a scaling group

Parameter	Description
Scaling Group Name	The name of a scaling group must be 2 to 64 characters in length, and can contain letters, digits, periods (.), underscores (_), and hyphens (-). The name must start with a letter or a digit.
Type	The type of instances that provide computing power in the scaling group. The type of instances that Auto Scaling adds to or removes from the scaling group during a scaling event also matches the value of the Type parameter. Valid values: ECS: ECS instances. ECI: elastic container instances.
Instance Configuration Source	The instance configuration source. Auto Scaling creates ECS instances in the scaling group based on the specified source. Valid values: Launch Templates: A launch template contains information such as the key pair, Resource Access Management (RAM) role, instance type, and network settings. A launch template does not contain passwords. The Launch Templates setting is available only if you set the Type parameter to ECS. Scale-out failures caused by insufficient resources may often occur if you specify only one instance type. You can configure the Extend Launch Template parameter to specify multiple instance types to improve the success rate of scale-out events. For more information, see Create a multi-instance type scaling group by using a launch template. Select Existing Instance: You must select an existing instance. Auto Scaling extracts the basic configurations of the instance to create a default scaling configuration. Important The basic configurations that are extracted from an existing ECS instance include the instance type, network type, security group, and base image. Take note that the instance logon password and tags are not extracted. The base image is the image of the existing ECS instance. The base image does not include instance data such as application data. If you want the scaling configuration created from an existing ECS instance to contain the system configurations and instance data of the ECS instance, you must create a custom image from the ECS instance. Create from Scratch: You can specify an instance configuration source after you create the scaling group. The instance configuration source can be a scaling configuration or a launch template. The steps that you must perform to create a scaling configuration vary based on the value of the Type parameter. For more information, see Create a scaling configuration of the ECS type and Create a scaling configuration of the Elastic Container Instance type. Note If you create a scaling group based on an existing ECS instance created in the ECS console, Auto Scaling automatically fills the instance configuration source and network type of the scaling group. We recommend that you retain the settings.
Suspend Process	You can suspend processes before you perform specific operations. For example, you can suspend the health check process before you stop an instance. This way, if the health check fails, the instance is not removed from the scaling group. You can suspend the following processes in a scaling group: Scale-out: If you suspend a process of this type, Auto Scaling rejects all scale-out requests. Scale-in: If you suspend a process of this type, Auto Scaling rejects all scale-in requests. Health Check: If you suspend a process of this type, Auto Scaling suspends health checks and does not remove unhealthy instances. Scheduled Task: If you suspend a process of this type, Auto Scaling does not execute the scaling rule that is associated with a scheduled task when the execution time of the scheduled task arrives. Event-triggered Task: If you suspend a process of this type, Auto Scaling does not execute the scaling rule that is associated with an event-triggered task when the event-triggered task enters the Alert state. For more information, see Suspend and resume scaling group processes.
Deletion Protection	After you enable this feature, you cannot delete the scaling group in the Auto Scaling console or by calling an API operation. This helps prevent scaling groups from being accidentally deleted.
Instance Health Check	After you enable this feature, Auto Scaling checks the status of instances on a regular basis. If Auto Scaling detects that an instance does not run as expected, Auto Scaling considers the instance unhealthy and removes the instance from the scaling group. For more information, see Instance lifecycles. Valid values: Disable: disables Instance Health Check. Instance Status Check: enables Instance Health Check. Load Balancer Health Check: enables Instance Health Check and uses the health check results of Application Load Balancer (ALB) or Network Load Balancer (NLB) instances as the basis for checking the health status of instances in the scaling group. The health check results of Classic Load Balancer (CLB) instances cannot be used to check the health status of instances in the scaling group.
Maximum Life Span of Instance (Seconds)	The maximum lifespan of each instance in the scaling group. When the lifespan of an instance in the scaling group exceeds the value of this parameter, Auto Scaling automatically creates a new instance to replace the instance. Note This parameter is available only if you set the Type parameter to ECS.

Parameters for configuring instance numbers

Parameter	Description
Minimum Number of Instances	The lower limit of the number of instances in the scaling group. If the actual number of instances drops below the lower limit, Auto Scaling automatically adds instances to the scaling group until the actual number reaches the lower limit.
Maximum Number of Instances	The upper limit of the number of instances in the scaling group. If the actual number of instances exceeds the upper limit, Auto Scaling automatically removes instances from the scaling group until the actual number equals the upper limit. For information about scale-in policies, see Combine scaling policies and scale-in policies.
Expected Number of Instances	The desired number of instances in the scaling group. If you enable this feature, Auto Scaling automatically ensures that the actual number of instances in the scaling group equals the desired number. For more information, see Expected number of instances.

Parameters for triggering scale-out or scale-in events

Important

If your scaling group is of the Elastic Container Instance type, you cannot modify the default settings of the following parameters: Scaling Policy, Scale-In Policy, and Instance Reclaim Mode. Default values of the parameters:

Scaling Policy: Cost Optimization Policy
Scale-In Policy: Instances Created From Earliest Scaling Configuration as the first scale-in step and Earliest Instances as the second scale-in step
Instance Reclaim Mode: Release

Parameter	Description
Scaling Policy	By default, Auto Scaling triggers scaling events in a scaling group based on the specified order (priority policy) of vSwitches. You can set the Scaling Policy parameter to other policies based on your business requirements. Important You can configure the Scaling Policy parameter only for scaling groups whose Type parameter is set to ECS and Network Type parameter is set to VPC. If your scaling group is of the ECI type, only the priority policy is supported. Priority policy (default) This policy adds or removes Elastic Compute Service (ECS) instances based on the specified vSwitches. If Auto Scaling cannot create ECS instances in the zone where the vSwitch with the highest priority resides, Auto Scaling creates ECS instances in the zone where the vSwitch with the next highest priority resides. Balanced distribution policy This policy ensures disaster recovery. If you want to evenly distribute ECS instances across the zones of your scaling group after scaling events are complete, use this policy. If ECS instances are not evenly distributed across multiple zones due to insufficient resources, execute the balanced distribution policy to evenly redistribute instances across the zones. For more information, see Rebalance the distribution of ECS instances. Cost optimization policy If you prioritize cost in your decision-making, use this policy. When a scale-out event occurs, Auto Scaling preferentially creates ECS instances by using the instance type that has the lowest-priced vCPU. If multiple preemptible instance types are specified in your scaling configuration, Auto Scaling preferentially creates preemptible instances. If Auto Scaling fails to create preemptible instances due to insufficient resources, Auto Scaling attempts to create pay-as-you-go instances. When a scale-in event occurs, Auto Scaling preferentially removes ECS instances of the instance type that has the highest-priced vCPU from your scaling group. Custom combination policy If you use this policy, you can adjust the ratio of pay-as-you-go instances to preemptible instances, balance instance distribution across zones, and specify instance types. For information about the custom combination policy, see Configure a scaling policy.
Scale-In Policy	When a scale-in request is triggered, Auto Scaling removes instances from the scaling group based on the steps defined in the scale-in policy. This parameter is displayed only if you set the Type parameter to ECS. Valid values: Instances Created From Earliest Scaling Configuration: Auto Scaling removes the instances created from the earliest scaling configuration from the scaling group. No scaling configuration or launch template is associated with instances that are manually added to the scaling group. Therefore, instances that are manually added are not removed first. If more instances need to be removed from the scaling group after Auto Scaling removes all instances with which the earliest scaling configuration or the earliest launch template is associated, Auto Scaling removes manually added instances at random. Important The scaling configuration in the Instances Created From Earliest Scaling Configuration setting can be a scaling configuration or a launch template. If the scaling configuration is a launch template, the point in time at which the launch template is applied in the scaling group matters. Example: If you apply a launch template of version 2 but subsequently roll back the launch template to version 1, the earliest scaling configuration in this case is the launch template of version 2. Earliest Instances: Auto Scaling removes the instances that were created at the earliest point in time from the scaling group. Most Recent Instances: Auto Scaling removes the instances that were created at the most recent point in time from the scaling group. Custom Policy: Auto Scaling removes instances from the scaling group based on a custom policy. The custom policy contains a service, version, and function. If more than one instance meets the scale-in requirements when you set the Scale-In Policy parameter to Instances Created From Earliest Scaling Configuration or Custom Policy, you can proceed to configure the Then Remove parameter. Valid values of the Then Remove parameter: No Policy: Auto Scaling stops removing instances from the scaling group even if multiple instances meet the scale-in requirements. Earliest Instances: Auto Scaling removes the instances that were created at the earliest point in time among the remaining instances from the scaling group. Most Recent Instances: Auto Scaling removes the instances that were created at the most recent point in time among the remaining instances from the scaling group. Note The value of the Scaling Policy parameter also affects the manner in which instances are removed from scaling groups. For more information, see Combine scaling policies and scale-in policies.
Instance Reclaim Mode	After an instance is removed from the scaling group, Auto Scaling reclaims the instance based on the value of this parameter. Valid values: Note This parameter is available only if you set the Type parameter to ECS and the Network Type parameter to VPC. By default, elastic container instances are released after they are removed from scaling groups. Release: releases instances that are removed from the scaling group. In this case, no resources are retained. If a scale-out request is triggered, Auto Scaling creates new instances and adds the instances to the scaling group. Economical Mode: stops instances that are removed from the scaling group in Economical Mode. In this case, you are still charged for resources that are retained. If a scale-out request is triggered, Auto Scaling preferentially adds the instances that are stopped in Economical Mode to the scaling group. If the number of instances that are in Economical Mode does not meet the scale-out requirement, Auto Scaling creates and adds new instances. The Economical Mode setting helps improve the efficiency of scaling. For more information, see Use the Economical Mode feature to scale instances faster. Valid values: Important Data that is stored on instances may be lost when the instances are reclaimed. To prevent data loss, do not store application data or logs on instances. In the following scenarios, instances that are stopped in Economical Mode may be released: If you manually change the value of the Maximum Number of Instances parameter for the scaling group and the number of instances in all states in the scaling group is greater than the new value of the Maximum Number of Instances parameter, Auto Scaling preferentially releases instances that are stopped in Economical Mode. If your Alibaba Cloud account has overdue payments or insufficient resources, instances that are stopped in Economical Mode may fail to be added to the scaling group during a scale-out event. In this case, Auto Scaling may release the failed instances. For more information about Economical Mode, see Economical mode. Forcibly Release: In this mode, Auto Scaling forcibly releases instances that are in the `Running` state when scale-in events are triggered. Warning Forced release is equivalent to a power outage. Forced release may cause ephemeral data on instances to be irrecoverably lost. Exercise caution when you specify this setting. Forcibly Recycle: In this mode, Auto Scaling forcibly shuts down instances that are in the `Running` state when scale-in events are triggered. Warning Forced shutdown is equivalent to a power outage. Forced shutdown may cause ephemeral data on instances to be irrecoverably lost. Exercise caution when you specify this setting.

Parameters for configuring a network

Important

When you set the Instance Configuration Source parameter to Launch Templates or Select Existing Instance, the following parameters are automatically filled based on the selected launch template or existing instance: Network Type, VPC, and vSwitch. You can also reconfigure these parameters based on your business requirements.

Parameter	Description
Network Type	Specify the network type for the scaling group that you want to create. Valid values: VPC and Classic Network. Warning After you create the scaling group, you cannot change the value of the Network Type parameter. Important We recommend that you select VPC. Scaling groups that reside in virtual private clouds (VPCs) support more flexible scaling policies, instance reclaim modes, and load balancing mechanisms. For more information about VPCs, see What is a VPC?
VPC	This parameter is displayed only if you set the Network Type parameter to VPC. After you select a VPC from the VPC drop-down list, all ECS instances in this scaling group reside in the VPC. Warning After you create the scaling group, you cannot change the value of the VPC parameter.
vSwitch	After you select a VPC for the scaling group, you must select one or more vSwitches of the VPC for the scaling group. All ECS instances in the scaling group communicate with each other by using the selected vSwitches. Important We recommend that you select multiple vSwitches. If you select only one vSwitch, scale-out failures caused by insufficient resources in a single zone may often occur. If you select multiple vSwitches, you can set the Scaling Policy parameter to Balanced Distribution Policy to manage the distribution of ECS instances across multiple zones.

Parameters for associating a scaling group with other cloud services

Parameter	Description
Associate with ApsaraDB RDS, Redis, or MongoDB	If ECS instances in the scaling group need to access a database such as ApsaraDB RDS, Redis, or MongoDB, you can associate the scaling group with the database by configuring this parameter. You can select one of the following association modes based on the type of database that you want to use: IP Whitelist Mode and Security Group Mode. Note An upper limit is imposed on the number of cloud databases that you can associate with a scaling group. To view the quota or request a quota increase, go to Quota Center. For information about the cloud databases supported by scaling groups, see Associate instances in a scaling group with cloud databases.
Associate CLB Instance	After you associate a CLB instance with a scaling group, Auto Scaling adds the instances in the scaling group to the backend server groups of the CLB instance as backend servers. Then, the CLB instance forwards requests to the backend servers. The following types of server groups are supported: Default server group: the group of instances that are used to receive requests. If you do not specify a vServer group or a primary/secondary server group for a listener, requests are forwarded to the instances in the default server group. vServer group: If you want to forward requests to backend servers that are not in the default server group or configure domain name- or URL-based routing methods, you can use vServer groups. If you specify the default server group and multiple vServer groups at the same time, the instances are added to all the specified server groups. Note An upper limit is imposed on the number of CLB instances and server groups that you can associate with a scaling group. To view the quota or request a quota increase, go to Quota Center.
Associate ALB and NLB Server Groups	Important This parameter is available only if you set the Network Type parameter to VPC. After you associate an ALB or NLB server group with a scaling group, Auto Scaling adds instances in the scaling group to the ALB or NLB server group as backend servers. Then, the ALB or NLB instance forwards requests to the backend servers. You must specify the port number and weight for each backend server. By default, the weight of a backend server is 50. If you increase the weight of a server, the number of requests that are forwarded to the server increases. If you set the weight of a backend server to 0, no requests are forwarded to the server. If you associate multiple ALB or NLB server groups with the same scaling group, Auto Scaling adds instances in the scaling group to all the ALB or NLB server groups at the same time. Note An upper limit is imposed on the number of ALB or NLB server groups that you can associate with a scaling group. To view the quota or request a quota increase, go to Quota Center.

Other parameters

Parameter	Description
Tag	You can add tags to scaling groups for easy search and aggregation. For more information, see Tags. Note The tags apply only to the scaling group. If you want to add tags to an instance in the scaling group, configure the tags in the scaling configuration or the launch template based on which the instance is created.
Tags Propagated to Instances During Scale-out	After you add one or more tags to the scaling group, you can continue to specify whether to propagate the tags to instances in the scaling group during scale-out events.
Add Existing Instance	This parameter is available only if you set the Type parameter to ECS and set the Instance Configuration Source parameter to Launch Templates or Select Existing Instance. If you configure the Expected Number of Instances and Add Existing Instance parameters at the same time, the value of the Expected Number of Instances parameter automatically increases. For example, if you set the Expected Number of Instances parameter to 1 and select two existing ECS instances from the Add Existing Instance drop-down list when you create the scaling group, the value of the Expected Number of Instances parameter automatically increases from 1 to 3. If you want to use the scaling group to manage the instance lifecycles, you can select Enable the scaling group to manage the instance lifecycle. If you enable this feature, Auto Scaling may remove instances that are considered unhealthy from the scaling group. Auto Scaling may also release the instances that you manually remove from the scaling group. If you do not enable this feature, Auto Scaling does not release instances that are removed from the scaling group. Note You can add subscription instances to the scaling group, but you cannot enable the scaling group to manage the lifecycles of the subscription instances.
Create Regular Rule	When a scaling event succeeds, fails, or is rejected, Auto Scaling notifies you by text message, internal message, or email based on the rule you set. For more information, see Create a regular notification rule.
Resource Group	You can add scaling groups to resource groups. Then, you can manage scaling groups by resource group. This facilitates resource isolation and permission control. For more information, see Use resource groups to manage scaling groups in a fine-grained manner.
Synchronize Alert Rule to CloudMonitor	You can enable or disable this feature only when you create a scaling group. After you enable this feature, Alibaba Cloud creates and associates a CloudMonitor application group with the scaling group. The alert rules of the scaling group are synced and displayed in the CloudMonitor console.