Adds backend servers to a listener.

Note If the backend servers added to a request are identical, only the first backend server added is accepted. The backend servers you want to add cannot be the same as existing backend servers. Otherwise, an error is reported.

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Request parameters

Parameter Type Required? Example value Description
Action String Yes AddBackendServers

The name of this action.

Value: AddBackendServers

LoadBalancerId String Yes lb-2ze7o5h52g02kkzz******

The ID of the Server Load Balancer (SLB) instance.

RegionId String Yes cn-beijing

The ID of the region to which the SLB instance belongs.

To query the region ID, call DescribeRegions.

BackendServers String Yes [{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "192.168. **. **", "Port":"80","Description":"test-112" },{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "172.166. **. **", "Port":"80","Description":"test-113" }]

The list of backend servers to be added.

The list must contain the following parameters:

  • ServerId: the instance ID of the backend server. It can be the instance ID of an Elastic Compute Service (ECS) instance or an Elastic Network Interface (ENI). It is a required parameter of string type. If the value of ServerId is the instance ID of an ENI, the ServerIp parameter and the Type parameter are required.
  • Weight: the weight of the backend server. Value range: 0 to 100. Default value: 100

    If the weight value of a backend server is 0, no request is distributed to this server.

  • Description: the description of the backend server. This parameter is optional and of string type. The description must be 1 to 80 characters in length and can contain letters, numbers, hyphens (-), forward slashes (/), periods (.), and underscores (_).
  • Type: the type of the backend server. Valid values:
    • ecs: ECS instance (default)
    • eni: ENI
  • ServerIp: the IP address of the ECS instance or ENI.


  • Example of adding an ECS instance: [{ "ServerId": "i-xxxxxxxxx", "Weight": "100", "Type": "ecs", "Port":"80","Description":"test-112" }]
  • Example of adding an ENI: [{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "192.168. **. **", "Port":"80","Description":"test-112" }]
  • Example of adding multiple ENIs: [{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "192.168. **. **", "Port":"80","Description":"test-112" },{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "172.166. **. **", "Port":"80","Description":"test-113" }]
  • Only backend servers in the running state can be added. You can add up to 20 backend servers at a time.
  • ENI-type backend servers are supported only by guaranteed-performance instances.

Response parameters

Parameter Type Example value Description
RequestId String 34B82C81-F13B-4EEB-99F6-A048C67CC830

The ID of the request.

LoadBalancerId String lb-2ze7o5h52g02kkzz****

The ID of the SLB instance.

BackendServers Array

The list of added backend servers.

ServerId String i-2zej4lxhjoq1icu*****

The instance ID of the backend server.

Weight String 100

The weight of the backend server.

Value range: 0 to 100

Default value: 100. If the value is set to 0, no requests are forwarded to the backend server.

Type String ecs

The type of the backend server.

  • ecs: ECS instance (default)
  • eni: ENI
Description String Backend server

The description of the backend server.


Request example

http(s)://[Endpoint]/? Action=AddBackendServers
&BackendServers=[{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "192.168. **. **", "Port":"80","Description":"test-112" },{ "ServerId": "eni-xxxxxxxxx", "Weight": "100", "Type": "eni", "ServerIp": "172.166. **. **", "Port":"80","Description":"test-113" }]

Response example

XML format


JSON format

    "RequestId": "34B82C81-F13B-4EEB-99F6-A048C67CC830",
    "BackendServers": {
        "BackendServer": [
                "ServerId": "i-2zej4lxhjoq1icue****",
                "Weight": 100,
                "Type": "ecs"
                "ServerId": "i-2ze1u9ywulp5pbvv****",
                "Weight": 100,
                "Type": "ecs"
    "LoadBalancerId": "lb-2ze7o5h52g02kkzze****"


HTTP status code Error code Error message Description
400 InvalidParameter The specified load balancer does not support the network type of the ECS instance. The network type of the specified ECS instance is not supported by the specified SLB instance.

For a list of error codes, visit the API Error Center.