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ENS:AddBackendServers

Last Updated:Mar 27, 2026

Adds backend servers.

Operation description

  • Rate limit: 100 requests per second.

  • up to 10 times per second per account.

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RAM authorization

The table below describes the authorization required to call this API. You can define it in a Resource Access Management (RAM) policy. The table's columns are detailed below:

  • Action: The actions can be used in the Action element of RAM permission policy statements to grant permissions to perform the operation.

  • API: The API that you can call to perform the action.

  • Access level: The predefined level of access granted for each API. Valid values: create, list, get, update, and delete.

  • Resource type: The type of the resource that supports authorization to perform the action. It indicates if the action supports resource-level permission. The specified resource must be compatible with the action. Otherwise, the policy will be ineffective.

    • For APIs with resource-level permissions, required resource types are marked with an asterisk (*). Specify the corresponding Alibaba Cloud Resource Name (ARN) in the Resource element of the policy.

    • For APIs without resource-level permissions, it is shown as All Resources. Use an asterisk (*) in the Resource element of the policy.

  • Condition key: The condition keys defined by the service. The key allows for granular control, applying to either actions alone or actions associated with specific resources. In addition to service-specific condition keys, Alibaba Cloud provides a set of common condition keys applicable across all RAM-supported services.

  • Dependent action: The dependent actions required to run the action. To complete the action, the RAM user or the RAM role must have the permissions to perform all dependent actions.

Action

Access level

Resource type

Condition key

Dependent action

ens:AddBackendServers

create

*All Resource

*

None None

Request parameters

Parameter

Type

Required

Description

Example

LoadBalancerId

string

Yes

The frontend port that is used by the Edge Load Balance (ELB) instance. Valid values: 1 to 65535.

lb-5qzdmxefgrpxd7oz2mefonvtx

BackendServers

array<object>

Yes

The list of backend servers that you want to add to the Edge Load Balancer (ELB) instance. You can add up to 20 backend servers at a time.

Note

Only Edge Node Service (ENS) instances that are in the running state can be added to the ELB instance as backend servers.

object

Yes

The list of backend servers that you want to add to the ELB instance. You can add up to 20 backend servers at a time.

Note

Only ENS instances that are in the running state can be added to the ELB instance as backend servers.

ServerId

string

Yes

The ID of the ENS instance.

i-5uf6dwyzch3wly790****

Weight

integer

No

The weight of the backend server. Default value: 100. Valid values: 0 to 100.

Note

The value 0 indicates that requests are not forwarded to the backend server.

100

Type

string

No

The type of the backend server. Valid values:

  • ens: ENS instance

  • eni: elastic network interface (ENI)

ens

Ip

string

No

The IP address of the backend server.

192.168.XXX

Port

integer

No

The backend port that is used by the ELB instance.

3309

Response elements

Element

Type

Description

Example

object

Schema of Response

RequestId

string

The request ID.

473469C7-AA6F-4DC5-B3DB-A3DC0DE3C83E

BackendServers

object

BackendServer

array<object>

The list of backend servers that you want to add. You can add at most 20 backend servers.

Note

Only ENS instances that are in the running state can be attached to the ELB instance as backend servers.

object

ServerId

string

The ID of the instance that is used as the backend server.

i-5uf6hj58zvml4ali8****

Weight

integer

The weight of the backend server. Default value: 100. Valid values: 0 to 100.

Note

The value 0 indicates that requests are not forwarded to the backend server.

100

Type

string

The type of the backend server. Valid values:

  • ens: ENS instance.

  • eni: ENI.

ens

Ip

string

The IP address of the backend server.

192.168.0.1

Port

integer

The backend port that is used by the ELB instance.

0

Examples

Success response

JSON format

{
  "RequestId": "473469C7-AA6F-4DC5-B3DB-A3DC0DE3C83E",
  "BackendServers": {
    "BackendServer": [
      {
        "ServerId": "i-5uf6hj58zvml4ali8****",
        "Weight": 100,
        "Type": "ens",
        "Ip": "192.168.0.1",
        "Port": 0
      }
    ]
  }
}

Error codes

HTTP status code

Error code

Error message

Description

400 ens.interface.error An error occurred while call the API.
400 LoadBalancerNotFound The input parameter loadBalancerId that is not found.
400 IncorrectInstanceStatus The current status of the resource does not support this operation. The current operation is not supported. The disk is being reset.
400 InstanceNotFound The input parameter instanceId that is not found.
400 InvalidParameter.Mismatch Specified loadbalancer and backendServer are not in the same network.
400 QuotaExceed.BackendServer Backend servers quota exceeded in this loadbalancer.
400 Missing%s You must specify the parameter %s.
400 Invalid%s The specified parameter %s is invalid.
400 InvalidParameter.EniType The type of eni is invalid
400 InvalidParameter.EniStatus The status of eni is invalid
400 InvalidParameter.EniServiceManaged The eni is managed by service
400 NoPermission Permission denied.
400 InvalidParameter.%s The specified field %s invalid. Please check it again.

See Error Codes for a complete list.

Release notes

See Release Notes for a complete list.