# Add backend instances for traditional load balancing - AllocateBackend

## Overview

Add CLB backend resource instance






## Definition

### Public Parameters

| Parameter Name | Type | Description Information | Required |
|:---|:---|:---|:---|
| **Action**     | string  | Corresponding API command name, the current API is `AllocateBackend`.                      | **Yes** |
| **PublicKey**  | string  | The user's public key can be obtained from [Console](https://console.scloudsg.com/uaccount/api_manage)                                             | **Yes** |
| **Signature**  | string  | User signature generated based on public key and API command, see [Signature Algorithm](/docs/api/summary/signature.md)  | **Yes** |

### Request Parameters

| Parameter Name | Type | Description Information | Required |
|:---|:---|:---|:---|
| **Region** | string | Region. See [List of Regions and Availability Zones](/docs/api/summary/regionlist) |**Yes**|
| **ProjectId** | string | Project ID. If not filled in, the default project is used, sub-accounts must be filled in. Please refer to the [GetProjectList interface](/docs/api/summary/get_project_list). |**Yes**|
| **ULBId** | string | ID of the traditional load balancing instance |**Yes**|
| **VServerId** | string | ID of the VServer instance |**Yes**|
| **ResourceType** | string | The type of the added backend resources, enumeration values: UHost -> Cloud host; UNI -> Virtual network card; UPM -> Physical cloud host; UHybrid->Hybrid cloud host; CUBE->Cube, IP->IP type; The default value is UHost. Packet forwarding mode does not support UHybrid, CUBE, IP. |**Yes**|
| **ResourceId** | string | The resource ID of the added backend resources; either this or ResourceIP must be filled in. |No|
| **ResourceIP** | string | The IP of the added backend server resource instance is valid when ResourceType is UHybrid or IP, and it is required; it is required to fill either this or ResourceId. |No|
| **VPCId** | string | The VPC where the added backend servers are located is effective when ResourceType is UHybrid or IP, and it is required. |No|
| **SubnetId** | string | The subnet where the added backend server is located is effective when ResourceType is UHybrid or IP, and it is mandatory. |No|
| **Port** | int | The backend resource service port you added, the value range is [1-65535], default is 80. |No|
| **Weight** | int | The weight of the added backend RS (effective under the weighted round-robin algorithm), the value range is [1-100], the default is 1. |No|
| **Enabled** | int | Backend instance status switch, enumeration values: 1: Enabled; 0: Disabled. The default is Enabled. |No|
| **IsBackup** | int | Whether rs is for backup, default is 0<br />0: ordinary rs<br />1: backup rs |No|

### Response Field

| Field Name | Type | Description Information | Required |
|:---|:---|:---|:---|
| **RetCode** | int | Return status code. If it is 0, it means successful return. If it is not 0, it means failure. |**Yes**|
| **Action** | string | Operation command name. |**Yes**|
| **Message** | string | Returns an error message, providing detailed description when `RetCode` is non-zero. |No|
| **BackendId** | string | The object ID of the added backend resource in CLB, (used in the CLB system, unrelated to the resource's own ID), can be used for UpdateBackendAttribute/UpdateBackendAttributeBatch/ReleaseBackend. |No|




## Example

### Request Example
    
```
https://api.scloudsg.com/?Action=AllocateBackend
&Region=cn-bj2
&ProjectId=project-XXXXX
&ULBId=ulb-XXXXX
&VServerId=vserver-XXXXX
&ResourceType=UHost
&ResourceId=uhost-XXXX 
&Port=80
&Enabled=1
&Weight=4
&IsBackup=4
&ResourceIP=ELVhVVux
&VPCId=qFbjvNJn
&SubnetId=DKBOyKER
```

### Response Example
    
```json
{
  "Action": "AllocateBackendResponse",
  "BackendId": "backend-XXXXX",
  "RetCode": 0
}
```