### Understand the alert

The `haproxy_backend_server_status` alert is triggered when one or more backend servers that are managed by HAProxy are inaccessible or offline. HAProxy is a reverse-proxy that provides high availability, load balancing, and proxying for TCP and HTTP-based applications. If you receive this alert, it means that there may be a problem with your backend server(s), and incoming requests could face delays or not be processed correctly.

### Troubleshoot the alert

1. **Check the HAProxy backend server status**

   You can check the status of each individual backend server by accessing the HAProxy Statistics Report. By default, this report can be accessed on the HAProxy server using the URL:

   ```
   http://<Your-HAProxy-Server-IP>:9000/haproxy_stats
   ```

   Replace `<Your-HAProxy-Server-IP>` with the IP address of your HAProxy server. If you have configured a different port for the statistics report, use that instead of `9000`.

   In the report, look for any backend server(s) with a `DOWN` status.

2. **Investigate the problematic backend server(s)**

   For each of the backend servers that are in a `DOWN` status, check the availability and health of the server. Make sure that the server is running, and check its resources (CPU, memory, disk space, network) to identify any potential issues.

3. **Validate the HAProxy configuration**

   As mentioned in the provided guide, it is essential to validate the correctness of the HAProxy configuration file. If you haven't already, follow the steps in the guide to check for any configuration errors or warnings.

4. **Check for recent changes**

   If the backend servers were previously working correctly, inquire about any recent changes to the infrastructure, such as software updates or configuration changes.

5. **Restart the HAProxy service**

   If the backend server(s) seem to be healthy, but the alert still persists, try restarting the HAProxy service:

   ```
   sudo systemctl restart haproxy
   ```

6. **Monitor the alert and backend server status**

   After applying any changes or restarting the HAProxy service, monitor the alert and the backend server status in the HAProxy Statistics Report to see if the issue has been resolved.

### Useful resources

1. [HAProxy Configuration Manual](https://cbonte.github.io/haproxy-dconv/2.0/configuration.html)
2. [HAProxy Log Customization](https://www.haproxy.com/blog/introduction-to-haproxy-logging/)
