This topic describes how to configure a Classic Load Balancer (CLB)instance. Before you can use a CLB instance to forward traffic, you must add at least one listener and one group of backend servers to the CLB instance. The following example describes how to add a TCP listener and two Elastic Compute Service (ECS) instances to a CLB instance. The ECS instances are named ECS 01 and ECS 02. The ECS instances function as backend servers and host static web pages.


  1. Log on to the CLB console.
  2. On the Instances page, find the CLB instance and click Configure Listener in the Actions column.
  3. In the Protocol and Listener wizard, set the following parameters and click Next.
    Parameter Description
    Select Listener Protocol Select the protocol of the listener.

    In this example, TCP is selected.

    Listening Port Specify the port that the CLB instance uses to receive requests and forward the requests to backend servers. In this example, the port number is set to 80.
    Note The ports on which a CLB instance listens must be unique.
    Listener Name Enter a name for the listener.
    Advanced Click Modify to configure advanced settings. In this topic, the default values are used. For more information, see Add a TCP listener.
  4. In the Backend Servers wizard, select a backend server type.
    In this topic, Default Server Group is selected. Click Add More.
    1. In the My Servers panel, select ECS 01 and ECS 02 that you created, and click Next.
    2. Set weights for the servers and click Add.
      A backend server that has a higher weight receives more requests. In this topic, the default values are used.
    3. On the Default Server Group tab, specify backend ports that are available to receive requests, and click Next.
      You can specify the same port for multiple backend servers of a CLB instance. In this example, the port number is set to 80.
  5. In the Health Check wizard, configure health checks and click Next. The default values are used in this topic.
    After you enable health checks for the CLB instance, the CLB instance periodically checks whether the backend ECS instances are healthy. When the CLB instance detects an unhealthy ECS instance, the CLB instance distributes the requests to other healthy ECS instances. When the unhealthy ECS instance recovers, the CLB instance starts to distribute requests to the ECS instance again.
  6. In the Configuration Review wizard, check the configuration and click Submit.
  7. Click OK to go back to the Instances page. Then, click the Refresh icon to refresh the page.
    If the health check status of a backend ECS instance is Active, the backend ECS instance is running as expected and is able to process requests forwarded by CLB.
  8. Enter the service address of the CLB instance into the address bar of the browser to check the connectivity. We recommend that you run the test multiple times.
    Figure 1. ECS01
    Figure 2. ECS02