# DescribeBackendHealth

## 1. API Description <a href="#id-1-api-description" id="id-1-api-description"></a>

This API is used to query the bound backend server list of a load balancer.

## 2. Input Parameters <a href="#id-2-input-parameters" id="id-2-input-parameters"></a>

The following request parameter list only provides API request parameters.

<table><thead><tr><th width="168.15765380859375">Parameter Name</th><th width="115.5390625">Required</th><th width="97.6854248046875">Type</th><th>Description</th></tr></thead><tbody><tr><td>loadBalancerId</td><td>Yes</td><td>String</td><td>Load balance instance ID.</td></tr><tr><td>listenerId</td><td>No</td><td>String</td><td><p>Load balance listener ID.</p><p>If not specified, all backend servers will be queried.</p></td></tr></tbody></table>

## 3. Output Parameters <a href="#id-3-output-parameters" id="id-3-output-parameters"></a>

<table><thead><tr><th width="160.38848876953125">Parameter Name</th><th width="215.7947998046875">Type</th><th>Description</th></tr></thead><tbody><tr><td>requestId</td><td>String</td><td>The unique request ID, which is returned for each request. RequestId is required for locating a problem.</td></tr><tr><td>backends</td><td>Array of <a href="../../data-types#listenerbackendhealth">ListenerBackendHealth</a></td><td>Health state of backend servers.</td></tr></tbody></table>

## 4. Code Example <a href="#id-4-code-example" id="id-4-code-example"></a>

{% tabs %}
{% tab title="Example" %}
**Query the health state of all bound backend servers of a load balancer.**

```json
POST /api/v2/zlb HTTP/1.1
Host: console.zenlayer.com
Content-Type: application/json
X-ZC-Action: DescribeBackendHealth
<Common Request Params>

Request：
{
  "loadBalancerId": "<loadBalancerId>"
}

Response：
{
  "requestId": "T23120DD8-C59C-4919-8F73-E3F3892D3CDC",
  "response": {
    "requestId": "T23120DD8-C59C-4919-8F73-E3F3892D3CDC",
    "backends": [
      {
        "listenerId": "<listenerId>",
        "protocol": "TCP",
        "instanceId": "<instanceId>",
        "backendPort": 1,
        "listenerName": "Listener-TCP-01",
        "weight": 100,
        "listenerPort": "8080",
        "privateIpAddress": "10.0.0.1"
        "healthStatus": "Alive"
      }
    ]
  }
}
```

{% endtab %}
{% endtabs %}

## 5. Developer Resources

Zenlayer Cloud API 2.0 [SDKs](https://docs.console.zenlayer.com/test/ci-develop-en/api-introduction/software-toolkit/sdk/introduction) to make it easier for you to call APIs. More programming languages will be supported.

## 6. Error Codes

No error codes related to the API business logic. For other error codes, see [Common Error Codes](https://docs.console.zenlayer.com/test/ci-develop-en/api-introduction/instruction/commonerrorcode).​
