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 Computing, click Auto 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
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
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.
The number of expected instances cannot be smaller than the minimum number of instances or greater than the maximum number of instances.
0
Min. Instances
Specifies the minimum number of ECS instances in an AS group.
0
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 three 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.
, 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
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 10 seconds, 1 minute, 5 minutes, 15 minutes, 1 hour, or 3 hours, based on the service requirements.
5 minutes
Advanced Settings
Configure notifications and tags.
You can select Do not configure or Configure now.
N/A
Notification Mode
This parameter is optional. If this parameter is selected, the system will notify you of scaling action results by email after a scaling action is complete.
The notifications will be sent to the email address you specified when you registered yourself on the cloud.
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 can include digits, letters, underscores (_), and hyphens (-).
Value
The value is optional.
A key can have only one value.
The value can include up to 43 characters. It can include digits, letters, underscores (_), and hyphens (-).
N/A
Click Next.
On the displayed page, you can use an existing AS configuration or create an AS configuration. For details, see Creating an AS Configuration from an Existing ECS Instance and Creating an AS Configuration from a New Specifications Template.
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. For details, see Dynamic Scaling and Scheduled Scaling.
Note
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.
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.