# Adding a Backend Server Group

#### Function

This API is used to add a backend server group. After multiple backend servers are added to a backend server group, requests are distributed among backend servers based on the load balancing algorithm configured for the backend server group and the weight set for each backend server.

#### Constraints

- Backend server groups using different protocols cannot be added to the same listener.
- If parameter session-persistence is configured, parameter cookie_name is available only when the value of type is APP_COOKIE.

#### URI

POST /v2.0/lbaas/pools

#### Request

Table 1 Parameter description
Parameter | Mandatory | Type | Description
--- | --- | --- | ---
pool | Yes | Object | Specifies the backend server group. For details, see Table 2.

Table 2 pool parameter description
Parameter | Mandatory | Type | Description
--- | --- | --- | ---
tenant_id | No | String | Specifies the ID of the project where the backend server group is used. The value must be the same as the value of project_id in the token. The value contains a maximum of 255 characters.
name | No | String | Specifies the name of the backend server group. The value contains a maximum of 255 characters.
description | No | String | Provides supplementary information about the backend server group. The value contains a maximum of 255 characters.

protocol

Yes

String

Specifies the protocol that the backend server group uses to receive requests.

TCP, UDP, and HTTP are supported.

When a backend server group is associated with a listener, the relationships between the protocol used by the listener and the protocol of the backend server group are as follows:

- When the protocol used by the listener is UDP, the protocol of the backend server group must be UDP.
- When the protocol used by the listener is TCP, the protocol of the backend server group must be TCP.
- When the protocol used by the listener is HTTP or TERMINATED_HTTPS, the protocol of the backend server group must be HTTP.

lb_algorithm

Yes

String

Specifies the load balancing algorithm of the backend server group.

The value can be one of the following:

- ROUND_ROBIN: indicates the weighted round robin algorithm.
- LEAST_CONNECTIONS: indicates the weighted least connections algorithm.
- SOURCE_IP: indicates the source IP hash algorithm.

When the value is SOURCE_IP, the weights of backend servers in the server group are invalid.

admin_state_up | No | Boolean | Specifies the administrative status of the backend server group. This parameter is reserved, and the default value is true.
listener_id | No | String | Specifies the ID of the listener associated with the backend server group. Specify either listener_id or loadbalancer_id, or both of them.
loadbalancer_id | No | String | Specifies the ID of the load balancer associated with the backend server group. Specify either listener_id or loadbalancer_id, or both of them.
session_persistence | No | Object | Specifies the sticky session timeout duration in minutes. For details, see Table 3. If the value is null, the sticky session feature is disabled.

Table 3 session_persistence parameter description
Parameter | Mandatory | Type | Description
--- | --- | --- | ---

type

Yes

String

Specifies the sticky session type.

The value can be one of the following:

- SOURCE_IP: Requests are distributed based on the client's IP address. Requests from the same IP address are sent to the same backend server.
- HTTP_COOKIE: When the client sends a request for the first time, the load balancer automatically generates a cookie and inserts the cookie into the response message. Subsequent requests are sent to the backend server that processes the first request.
- APP_COOKIE: When the client sends a request for the first time, the backend server that receives the request generates a cookie and inserts the cookie into the response message. Subsequent requests are sent to this backend server.

When the protocol of the backend server group is TCP, only SOURCE_IP takes effect. When the protocol of the backend server group is HTTP, only HTTP_COOKIE or APP_COOKIE takes effect.

cookie_name | No | String | Specifies the cookie name. This parameter is mandatory when the sticky session type is APP_COOKIE.

persistence_timeout

No

Integer

Specifies the sticky session timeout duration in minutes.

This parameter is invalid when type is set to APP_COOKIE.

The value range varies depending on the protocol of the backend server group:

- When the protocol of the backend server group is TCP or UDP, the value ranges from 1 to 60.
- When the protocol of the backend server group is HTTP or HTTPS, the value ranges from 1 to 1440.

#### Response

Table 4 Response parameters
Parameter | Type | Description
--- | --- | ---
pool | Object | Specifies the backend server group. For details, see Table 5.

Table 5 pools parameter description
Parameter | Type | Description
--- | --- | ---
id | String | Specifies the ID of the backend server group.
tenant_id | String | Specifies the ID of the project where the backend server group is used. The value contains a maximum of 255 characters.
name | String | Specifies the name of the backend server group. The value contains a maximum of 255 characters.
description | String | Provides supplementary information about the backend server group. The value contains a maximum of 255 characters.

protocol

String

Specifies the protocol that the backend server group uses to receive requests.

TCP, UDP, and HTTP are supported.

When a backend server group is associated with a listener, the relationships between the protocol used by the listener and the protocol of the backend server group are as follows:

- When the protocol used by the listener is UDP, the protocol of the backend server group must be UDP.
- When the protocol used by the listener is TCP, the protocol of the backend server group must be TCP.
- When the protocol used by the listener is HTTP or TERMINATED_HTTPS, the protocol of the backend server group must be HTTP.

lb_algorithm

String

Specifies the load balancing algorithm of the backend server group.

The value can be one of the following:

- ROUND_ROBIN: indicates the weighted round robin algorithm.
- LEAST_CONNECTIONS: indicates the weighted least connections algorithm.
- SOURCE_IP: indicates the source IP hash algorithm. When the value is SOURCE_IP, the weights of backend servers in the server group are invalid.

members | Array | Lists the IDs of backend servers in the backend server group.
healthmonitor_id | String | Specifies the ID of the health check configured for the backend server group.

admin_state_up

Boolean

Specifies the administrative status of the backend server group.

This parameter is reserved. The value can be true or false.

- true: Enabled
- false: Disabled

listeners | Array | Lists the IDs of listeners associated with the backend server group.
loadbalancers | Array | Lists the IDs of load balancers associated with the backend server group.
session_persistence | Object | Specifies whether to enable sticky sessions. For details, see Table 9. Once sticky session are enabled, requests from the same client are sent to the same backend server during the session. When sticky sessions are disabled, the value is null.

Table 6 members parameter description
Parameter | Type | Description
--- | --- | ---
id | String | Specifies the ID of the associated backend server.

Table 7 listeners parameter description
Parameter | Type | Description
--- | --- | ---
id | String | Specifies the ID of the associated backend server group.

Table 8 loadbalancers parameter description
Parameter | Type | Description
--- | --- | ---
id | String | Specifies the ID of the associated load balancer.

Table 9 session_persistence parameter description
Parameter | Type | Description
--- | --- | ---

type

String

Specifies the sticky session type.

The value can be one of the following:

- SOURCE_IP: Requests are distributed based on the client's IP address. Requests from the same IP address are sent to the same backend server.
- HTTP_COOKIE: When the client sends a request for the first time, the load balancer automatically generates a cookie and inserts the cookie into the response message. Subsequent requests are sent to the backend server that processes the first request.
- APP_COOKIE: When the client sends a request for the first time, the backend server that receives the request generates a cookie and inserts the cookie into the response message. Subsequent requests are sent to this backend server.

When the protocol of the backend server group is TCP, only SOURCE_IP takes effect. When the protocol of the backend server group is HTTP, only HTTP_COOKIE or APP_COOKIE takes effect.

cookie_name | String | Specifies the cookie name. This parameter is mandatory when the sticky session type is APP_COOKIE.

persistence_timeout

Integer

Specifies the sticky session timeout duration in minutes.

This parameter is invalid when type is set to APP_COOKIE.

- Optional value ranges are as follows:
  - When the protocol of the backend server group is TCP or UDP, the value ranges from 1 to 60.
  - When the protocol of the backend server group is HTTP or HTTPS, the value ranges from 1 to 1440.

#### Example Request

- Example request 1: Adding a backend server group with the sticky session feature disabled

      POST https://{Endpoint}/v2.0/lbaas/pools

      {
          "pool": {
              "lb_algorithm":"ROUND_ROBIN",
              "loadbalancer_id": "63ad9dfe-4750-479f-9630-ada43ccc8117",
              "protocol":"HTTP"
          }
      }

- Example request 2: Adding an HTTP backend server group with the value of type set to APP_COOKIE

      POST https://{Endpoint}/v2.0/lbaas/pools

      {
        "pool": {
          "lb_algorithm": "ROUND_ROBIN",
          "listener_id": "370fb112-e920-486a-b051-1d0d30704dd3",
          "protocol": "HTTP",
          "session_persistence": {
            "cookie_name": "my_cookie",
            "type": "APP_COOKIE",
            "persistence_timeout": 1
          },
          "admin_state_up": true
        }
      }

- Example request 3: Adding an HTTP backend server group with the value of type set to HTTP_COOKIE

      POST https://{Endpoint}/v2.0/lbaas/pools

      {
          "pool": {
              "lb_algorithm":"ROUND_ROBIN",
              "loadbalancer_id": "63ad9dfe-4750-479f-9630-ada43ccc8117",
              "protocol":"HTTP",
              "session_persistence":{
              	"type":"HTTP_COOKIE"
              }
          }
      }

#### Example Response

- Example response 1

      {
          "pool": {
              "lb_algorithm": "ROUND_ROBIN",
              "protocol": "HTTP",
              "description": "",
              "admin_state_up": true,
              "loadbalancers": [
                  {
                      "id": "63ad9dfe-4750-479f-9630-ada43ccc8117"
                  }
              ],
              "tenant_id": "601240b9c5c94059b63d484c92cfe308",
              "session_persistence": null,
              "healthmonitor_id": null,
              "listeners": [],
              "members": [],
              "id": "4e496951-befb-47bf-9573-c1cd11825c07",
              "name": ""
          }
      }

- Example response 2

      {
        "pool": {
          "lb_algorithm": "ROUND_ROBIN",
          "protocol": "HTTP",
          "description": "",
          "admin_state_up": true,
          "loadbalancers": [
            {
              "id": "6b041b9e-976b-40ba-b075-375be6110b53"
            }
          ],
          "tenant_id": "145483a5107745e9b3d80f956713e6a3",

          "session_persistence": {
            "cookie_name": "my_cookie",
            "type": "APP_COOKIE",
            "persistence_timeout": 1
          },
          "healthmonitor_id": null,
          "listeners": [
            {
              "id": "370fb112-e920-486a-b051-1d0d30704dd3"
            }
          ],
          "members": [

          ],
          "id": "307f8968-9474-4d0c-8434-66be09dabcc1",
          "name": ""
        }
      }

- Example response 3

      {
          "pool": {
              "lb_algorithm": "ROUND_ROBIN",
              "protocol": "HTTP",
              "description": "",
              "admin_state_up": true,
              "loadbalancers": [
                  {
                      "id": "63ad9dfe-4750-479f-9630-ada43ccc8117"
                  }
              ],
              "tenant_id": "601240b9c5c94059b63d484c92cfe308",
              "session_persistence": {
                  "persistence_timeout": 1440,
                  "cookie_name": null,
                  "type": "HTTP_COOKIE"
              },
              "healthmonitor_id": null,
              "listeners": [],
              "members": [],
              "id": "d46eab56-d76b-4cd3-8952-3c3c4cf113aa",
              "name": ""
          }
      }

#### Status Code

For details, see HTTP Status Codes of Shared Load Balancers.

Parent topic: Backend Server Group