This topic describes how to use Cloud Assistant to execute a health check script on Elastic Compute Service (ECS) instances and view the health check results. Heath check scripts are generated based on the health check configurations of listeners. You can manually execute a health check script after you attach backend servers to a Classic Load Balancer (CLB) instance.


To execute a health check script on backend servers, make sure that the following requirements are met:
  • Your CLB service is granted the required permissions to perform health checks on ECS instances. To grant the permissions, go to RAM Roles.
  • The backend servers that you want to check must be ECS instances that run Linux, the default Linux shell must be Bash, and Cloud Assistant must have been installed on the ECS instances. In addition, the ECS instances must be deployed in a virtual private cloud (VPC) and they must be in the Running state.
  • Health checks are enabled for the listener of the CLB instance, and the ECS instances are added to the backend server group.

Background information

Before you execute a health check script, take note of the following items:
  • You cannot execute a health check script on backend servers that are associated with forwarding rules.
  • The heath check results returned after you execute a script may differ from those after the system automatically performs a health check. This is because different connections are used to perform these health checks. The health check results returned upon a script execution only provide you with suggestions on health check configurations. For backend server troubleshooting, the health check results returned upon scheduled health checks shall prevail.


  1. Log on to the CLB console.
  2. Find the CLB instance for which you want to check backend servers and click its ID.
  3. On the Listener tab, find the listener that you want to manage and click Modify Listener in the Actions column.
  4. On the Configure Listener page, click Next until the Health Check step appears.
  5. Click Health Precheck in the Advanced section.
  6. On the Health Precheck page, find the backend server on which you want to execute a health check script and click Start Precheck in the Actions column.
    You can select up to five ECS instances at a time. If you want to execute the health check script on more than five ECS instances, divide these ECS instances into batches.
  7. Click OK to execute the health check script. After the health check script is executed, the result is displayed in the console.
    The following table describes the check items that are supported by listeners.
    Listener type Status of health check ports iptables configuration rpfilter configuration Response upon HTTP probing UDP probing
    TCP -
    UDP -
    HTTP -
    HTTPS -

    To view the script execution result in details, log on to the Cloud Assistant console, select the region where the ECS instance is deployed, and then click the Tasks tab.