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ENS:AddBackendServers

Last Updated:Jul 31, 2026

Adds backend servers.

Operation description

  • API call rate limit: 100 calls per second.

  • Per-user call rate limit: 10 calls per second.

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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 used by the load balancing instance. Valid values: 1 to 65535.

lb-5qzdmxefgrpxd7oz2mefonvtx

BackendServers

array<object>

Yes

The list of backend servers to add. You can add up to 20 backend servers per invoke.

Note

Backend servers (ENS instances) must be in the Running state before they can be added to a load balancing instance.

object

Yes

The list of backend servers to add. You can add up to 20 backend servers per invoke.

Note

Backend servers (ENS instances) must be in the Running state before they can be added to a load balancing instance.

ServerId

string

Yes

The ENS instance ID.

i-5uf6dwyzch3wly790****

Weight

integer

No

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

Note

A value of 0 indicates that no requests are forwarded to the backend server.

100

Type

string

No

The backend server type. Valid values:

  • ens: ENS instance.

  • eni: network interface controller (NIC) instance.

Valid values:

  • eni :

    Network interface controller (NIC)

  • ip :

    IP address.

  • ens :

    ENS instance.

ens

Ip

string

No

The IP address of the backend server.

192.168.XXX

Port

integer

No

The backend port used by the load balancing 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 to add. You can add up to 20 backend servers per invoke.

Note

Backend servers (ENS instances) must be in the Running state before they can be added to a load balancing instance.

object

The list of backend servers.

ServerId

string

The instance ID of the backend server.

i-5uf6hj58zvml4ali8****

Weight

integer

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

Note

A value of 0 indicates that no requests are forwarded to the backend server.

100

Type

string

The backend server type. Valid values:

  • ens: ENS instance.

  • eni: network interface controller (NIC) instance.

ens

Ip

string

The IP address of the backend server.

192.168.0.1

Port

integer

The backend port used by the load balancing 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.