A target group is a logical grouping used by Application Load Balancer (ALB) to manage a group of backend services. ALB forwarding rules distribute client requests to the backend services within a target group by routing them to that target group. A single target group can be associated with and referenced by multiple listeners or forwarding rules. Consequently, the same group of backend services can be reused across different listening scenarios.
This document describes how to create a target group, configure backend services for a target group, and edit or delete a target group in the ALB console.
Prerequisites
Backend services such as Cloud Virtual Machine (CVM) and Elastic Network Interface (ENI) for hosting your business have been created in the same virtual private cloud (VPC) as the target group, and the business applications have been deployed.
Attention:
Key attributes of a target group, such as its backend protocol and VPC, cannot be modified after creation. Confirm your configuration in advance based on your business plan.
Backend services added to a target group must reside in the same VPC as the target group.
Creating a Target Group
1. Log in to the ALB console. In the left sidebar, choose ALB > Target Group Management. 2. Select the region where the target group resides at the top of the page and click Create. The Create Target Group dialog box is displayed.
3. Configure parameters in the Basic Information section and click Next: Configure Health Check.
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Target Group Type | Select the type of the backend service that the target group carries. Currently, only instances are supported. |
Target Group Name | Enter a target group name, which is used for identification and management in a convenient manner. It can contain up to 60 characters. |
VPC | Select the VPC to which the target group belongs. The backend services added to a target group must belong to the same VPC as the target group. If the existing network is not suitable, click Create VPC to create one. |
Backend Protocol | Select the communication protocol between ALB and backend services. HTTP, HTTPS, gRPC, and gRPCs are supported. |
Balancing Method | Select a traffic distribution algorithm for multiple backend services within a target group. The following two methods are supported: weighted round robin (WRR) and weighted least connections (WLC). For details, see Balancing Methods. |
Session Persistence | After it is enabled, ALB distributes requests from the same client to the same real server. For details, see Session Persistence. |
Persistent Connection | After it is enabled, the number of connections between ALB and backend services fluctuates within the range of [QPS, QPS x 60]. The specific value depends on the connection reuse rate. If a limit is imposed on the number of connections to backend services, proceed with caution. |
Tag | You can select a tag key and a tag value or add a tag. For details, see Creating a Tag. |
4. Configure parameters in the Health Check section and click Complete.
A health check is used to probe the availability of backend services within a target group. After it is enabled, abnormal backend services are automatically checked and removed to ensure business high availability. For health check configurations, see Configuring a Health Check. Configuring Backend Services for a Target Group
Adding Backend Services
After a target group is created, you need to add backend services to it. Only then can business traffic be forwarded to the backend.
1. In the target group management list, click the target group name to go to the target group details page.
2. Select the Instances in Target Group tab and click Add.
3. In the Add Backend Service panel, select backend services and click Next: Configure Port and Weight.
4. Set the ports and weights for the selected backend services and click OK.
The configurable port range is 1–65535.
A higher weight results in more requests being forwarded. The default weight is 10, and the configurable range is 0–100. When the weight is set to 0, the server no longer accepts new requests.
Managing Backend Services
Go to the Instances in Target Group tab on the target group details page and perform the following management operations on backend services:
Add: Click Add and add backend services to the target group by following the instructions in Adding Backend Services. Modify Weight: In the Weight column of the target list, click the edit icon to adjust the weight of a single backend service. Alternatively, select the backend services whose weights you want to adjust and click Modify Weight to make the adjustment.
Remove: In the Operation column of the target record, click Remove to remove the target backend service from the target group.
Note:
Before a backend service is removed, we recommend that you first adjust its weight to 0. Remove the service only after the existing connections on it are processed to avoid service interruption. The removal operation does not affect the backend service itself (it does not terminate the instance).
Editing or Deleting a Target Group
Editing a target group: In the target group management list, locate the corresponding target group and click Edit in the Operation column. Alternatively, click the target group name to go to its details page. On the Basic Information tab, click the edit icon next to the corresponding attribute to complete the modification.
Deleting a target group: In the target group management list, locate the corresponding target group and click Delete in the Operation column. Then, click Confirm in the Confirmation dialog box to complete the deletion.
Attention:
A target group associated with an ALB instance cannot be deleted. Before you can delete it, remove its references in the corresponding listener and forwarding rule.
Deleting a target group does not affect the backend services within it. It only removes the logical grouping of backend services from the target group.