Creating an AS Group

Scenarios

An AS group consists of a collection of instances and AS policies that have similar attributes and apply to the same application scenario. An AS group is the basis for enabling or disabling AS policies and performing scaling actions. The pre-configured AS policy automatically adds or deletes instances to or from an AS group, or maintains a fixed number of instances in an AS group.

When creating an AS group, specify an AS configuration for it. Additionally, add one or more AS policies for the AS group.

Creating an AS group involves the configuration of the maximum, minimum, and expected numbers of instances and the associated load balancer.

Notes

ECS types available in different AZs may vary. When creating an AS group, choose an AS configuration that uses an ECS type available in the AZs used by the AS group.

If the ECS type specified in the AS configuration is not available in any of the AZs used by the AS group, the following situations will occur:
- If the AS group is disabled, it cannot be enabled again later.
- If the AS group is enabled, its status will become abnormal when instances are added to it.
If the ECS type specified in the AS configuration is only available in certain AZs used by the AS group, the ECS instances added by a scaling action are only deployed in the AZs where that ECS type is available. As a result, the instances in the AS group may not be evenly distributed.

Procedure

Log in to the management console.
Under Compute, click Auto Scaling. In the navigation pane on the left, choose Instance Scaling.
Click Create AS Group.

Set parameters, such as Name, Max. Instances, Min. Instances, and Expected Instances. Table 1 describes the key parameters to be configured.

**Table 1** AS group parameters
Parameter	Description	Example Value
Region	A region is where the AS group is deployed. Resources in different regions cannot communicate with each other over internal networks. For lower network latency and faster access to your resources, select the region nearest to your target users.	N/A
AZ	An AZ is a physical location where resources use independent power supply and networks. AZs are physically isolated but interconnected through an internal network. If you require high availability, buy servers in different AZs. If you require low network latency, buy servers in the same AZ.	N/A
Multi-AZ Scaling Policy	This parameter can be set to Balanced or Sequenced. Balanced: When scaling out an AS group, the system preferentially distributes ECS instances evenly across AZs used by the AS group. If it fails in the target AZ, it automatically selects another AZ based on the sequenced policy. Sequenced: When scaling out an AS group, the system distributes ECS instances to the AZ selected according to the order in which AZs are specified. NOTE: This parameter needs to be configured when two or more AZs are selected.	Balanced
Name	Specifies the name of the AS group to be created. The name can contain up to 64 characters. It can include letters, digits, underscores (_), and hyphens (-).	N/A
Max. Instances	Specifies the maximum number of ECS instances in an AS group.	1
Expected Instances	Specifies the expected number of ECS instances in an AS group. After an AS group is created, you can change this value, which will trigger a scaling action.	0
Min. Instances	Specifies the minimum number of ECS instances in an AS group.	0
AS configuration	Specifies the required AS configuration for the AS group. An AS configuration defines the specifications of the ECS instances to be added to an AS group. The specifications include the ECS image and system disk size. You need to create the required AS configuration before creating an AS group.	N/A
VPC	Provides a network for your ECS instances. All ECS instances in the AS group are deployed in this VPC.	N/A
Subnet	You can select up to five subnets. The AS group automatically binds all NICs to the created ECS instances. The first subnet is used by the primary NIC of an ECS instance by default, and other subnets are used by extension NICs of the instance.	N/A
Load Balancing	This parameter is optional. A load balancer automatically distributes traffic across all instances in an AS group to balance their service load. It improves the fault tolerance of your applications and expands application service capabilities. NOTE: Up to six load balancers can be added to an AS group. After multiple load balancers are added to an AS group, multiple services can be concurrently listened to, thereby improving service scalability. If ELB health check is selected for Health Check Method, when any one of the listeners detects that an instance becomes unhealthy, AS will replace it with a new one. If you select Elastic load balancer, configure the following parameters: Load Balancer Backend ECS Group Backend Port: specifies the port on which a backend ECS listens for traffic. Weight: determines the portion of requests a backend ECS processes compared to other backend ECSs added to the same listener. For more information about load balancing, see Elastic Load Balance User Guide.	N/A
Instance Removal Policy	Controls which instances are first to be removed during scale in. If specified conditions are met, scaling actions are triggered to remove instances. You can choose from any of the following instance removal policies: Oldest instance created from oldest AS configuration: The oldest instance created from the oldest configuration is removed from the AS group first. Newest instance created from oldest AS configuration: The newest instance created from the oldest configuration is removed from the AS group first. Oldest instance: The oldest instance is removed from the AS group first. Newest instance: The latest instance is removed from the AS group first. NOTE: AS always balances instances across AZs first, regardless of which removal policy is used. Manually added ECS instances are the last to be removed. If AS does remove a manually added instance, it only removes the instance from the AS group. It does not delete instance. If multiple manually added instances must be removed, AS preferentially removes the earliest-added instance first.	Oldest instance created from oldest AS configuration
EIP	If EIP has been selected in an AS configuration for an AS group, an EIP is automatically bound to the ECS instance added by a scaling action to the AS group. If you select Release, the EIP bound to an instance is released when the instance is removed from the AS group. Otherwise, the system unbinds the EIP from the instance, but does not release it when the instance is removed from the AS group.	N/A
Data Disk	If Data Disk is configured in the AS configuration used by the AS group, a data disk will be automatically created and attached to the ECS instances added during a scaling action to the AS group. If you select Release, the data disks attached to an instance will be deleted when the instance is removed from the AS group. Otherwise, the system detaches the data disks from the instance, but does not release them when the instance is removed from the AS group.	N/A
Health Check Method	When a health check detects an unhealthy ECS instance, AS replaces it with a new one. You can choose from either of the following health check methods: ECS health check: checks ECS instance health status. If an instance is stopped or deleted, it is considered to be unhealthy. This method is selected by default. Using this method, the AS group periodically evaluates the running status of each instance based on the health check results. If the health check results show that an instance is unhealthy, AS removes the instance from the AS group. ELB health check: determines ECS running status using a load balancing listener. When a load balancing listener detects that an instance is unhealthy, AS removes the instance from the AS group.	N/A
Health Check Interval	Specifies the length of time between health checks. You can set a health check interval, such as 5 minutes, 15 minutes, 1 hour, or 3 hours, based on the service requirements.	5 minutes
Enterprise Project	Specifies the enterprise project to which the AS group belongs. If an enterprise project is configured for an AS group, ECSs created in this AS group also belong to this enterprise project. If you do not specify an enterprise project, the default enterprise project will be used. NOTE: Value default indicates the default enterprise project. Resources that are not allocated to any enterprise projects under your account are displayed in the default enterprise project. Enterprise project is an upgraded version of IAM. It allocates and manages resources of different projects.	N/A
Tag	If you have many resources of the same type, you can use tags to manage your resources. You can identify specified resources quickly using the tags allocated to them. Each tag contains a key and a value. You can specify the key and value for each tag. Key The key must be specified. The key must be unique to the AS group. The key can include up to 36 characters. It cannot contain non-printable ASCII characters (0–31) or the following characters: =<>\,\|/ Value The value is optional. A key can have only one value. The value can include up to 43 characters. It cannot contain non-printable ASCII characters (0–31) or the following characters: =<>\,\|/	N/A

Click Next.
On the displayed page, you can use an existing AS configuration or create an AS configuration.
Click Next.
(Optional) Add an AS policy to an AS group.
On the displayed page, click Add AS Policy.
Configure the required parameters, such as the Policy Type, Scaling Action, and Cooldown Period.
- If a scaling action is triggered by an AS policy, the cooldown period is whatever configured for that AS policy.
- If a scaling action is triggered by manually changing the expected number of instances or by other actions, the cooldown period is whatever configured for the AS group. The default cooldown period is 300 seconds.
Click Create Now.
Check the AS group, AS configuration, and AS policy information. Click Submit.
Confirm the creation result and go back to the AS Groups page as prompted.
After the AS group is created, its status changes to Enabled.