Add backend servers to the default server group

Each Classic Load Balancer (CLB) instance has a default server group. You can add backend servers to the default server group. On a CLB instance, all listeners share the default server group. This topic describes how to add and manage backend servers in the default server group.

Prerequisites

Before you add a backend server to the default server group, make sure that the following requirements are met:

A CLB instance is created. For more information, see Create and manage a CLB instance.
ECS instances are created and applications are deployed on the ECS instances to receive requests. For more information, see the following topics:
- Purchase an ECS instance
- Create an ENI
Important
Make sure that the ECS instances and the CLB instance are in the same region.

Log on to the CLB console.
In the top navigation bar, select the region where the CLB instance is deployed.
On the Instances page, click the ID of the CLB instance that you want to manage.
Click the Default Server Group tab and click Add.
In the Servers panel, select a backend server type and a backend server, and then click Next.
To select an elastic network interface (ENI) as a backend server, make sure that the ECS instance is associated with the ENI. For more information, see Add backend servers by specifying ENIs.

In the Ports/Weights step, specify a weight for the backend server and click Add.
A backend server that has a higher weight receives more requests. To modify the weights of multiple backend servers, click the icon.
- Replicate to Below: The weights of all backend servers below the current server are set to the weight of the current server.
- Replicate to Above: The weights of all backend servers above the current server are set to the weight of the current server.
- Replicate to All: The weights of all backend servers in the default server group are set to the weight of the current server.
- Reset: If you click Reset on the right side of Weight, the weights of all ECS instances in the server group are set to the default value.
Important
- Valid values: 0 to 100. If the weight of a backend server is set to 0, no requests are sent to the backend server.
- You can specify server ports the in the default server group only when you create the listener. On the same listener, the ports of servers in the default server group must be the same.
In the Servers to Add panel, confirm the configurations and click OK. In the message that appears, click OK.
To add more backend servers, click Add More in the Servers to Add panel.

Manage servers in the default server group

After you add backend servers to the default server group, you can modify the weights of the backend servers. If you do not want a backend server to forward network traffic, remove the backend server.

Log on to the CLB console.
In the top navigation bar, select the region where the CLB instance is deployed.
On the Instances page, click the ID of the CLB instance that you want to manage.
Click the Default Server Group tab. On this tab, you can manage the backend servers.
- Modify the weights of backend servers:
  1. Find the backend server that you want to manage, move the pointer over the weight specified for the backend sever, and then click the icon.
  2. In the dialog box that appears, modify the weight of the backend server and click OK.
    Important
    Valid values: 0 to 100. If the weight of a backend server is set to 0, no requests are sent to the backend server.
- Remove backend servers:
  1. Find the backend server that you want to remove and click Remove in the Operations column.
  2. In the OK message, click Remove.

References

AddBackendServers: adds backend servers to the default server group.
SetBackendServers: modifies the weights of backend servers in the default server group.
RemoveBackendServers: removes backend servers form the default server group.