tencent cloud


Configuring Classic CLB

Last updated: 2021-07-07 10:11:48

    After creating a classic CLB instance, you need to configure a listener for it. The listener listens to requests on the instance and distributes traffic to real servers based on the load balancing policy.


    You need to create a CLB instance first and select "Classic CLB" for Instance type.


    Currently, there are two types of Tencent Cloud accounts: bill-by-EIP/CLB and bill-by-CVM. All Tencent Cloud accounts registered after June 17, 2020 00:00:00 are bill-by-EIP/CLB accounts. For Tencent Cloud accounts registered before June 17, 2020, check your account types in the console. Bill-by-EIP/CLB accounts no longer support classic CLB. You can now only purchase a CLB instance.

    Configuring the Listener

    Step 1. Open the Listener Management page

    1. Log in to the CLB Console.
    2. Select CLB Instance List on the left sidebar.
    3. On the Instance Management page, click the ID/Name of the instance to be configured to enter the instance details page.
    4. Select the Listener Management tab, or click Configure listener under the Operation column on the Instance Management page.
    5. The Listener Management page is as shown below.

    Step 2. Configure a listener

    Click Create under Listener Management and configure a TCP listener in the pop-up window.

    1. Basic configuration

    Configuration Item Description Example
    Name Listener name. test-tcp-80&dxnbsp;&dxnbsp;&dxnbsp;&dxnbsp;
    Listener Protocol Ports Listener protocol and listening port
  • Listener protocol: CLB supports protocols such as TCP, UDP, HTTP, and HTTPS. This example uses TCP.
  • Listening port: used to receive and forward requests to real servers. The port range is 1-65535.
  • The listening port must be unique in the same CLB instance.
  • TCP:80
    Backend Port The port through which the CVM instance provides services, receives and processes traffic from a CLB instance. 80

    To create a TCP listener, complete the basic configuration as shown below:

    2. Advanced configuration

    Configuration Item Description Example
    Balance Method For TCP listeners, CLB supports two scheduling algorithms: weighted round robin (WRR) and weighted least-connection (WLC).
  • WRR: requests are forwarded to different real servers sequentially according to their weights. Scheduling is based on the number of new connections, where servers with higher weights have more polls (i.e., a higher probability) and servers with the same weight process the same number of connections.
  • WLC: loads on servers are estimated according to their number of active connections. Scheduling is based on server loads and weights. If their weights are the same, real servers with fewer active connections will have more polls (i.e., a higher probability).
  • WRR
    Session Persistence Whether to enable or disable session persistence.
  • After session persistence is enabled, CLB listener will distribute access requests from the same client to the same real server.
  • TCP session persistence is implemented based on client IP address. The access requests from the same IP address are forwarded to the same real server.
  • Session persistence can be enabled for WRR scheduling but not WLC scheduling.
  • Enabled
    Hold Time Session persistence time.
  • If there is no new request in the connection within the session persistence time, session persistence will be automatically disconnected.
  • Value range: 30-3600 seconds.
  • 30s

    Complete the configuration as shown below:

    3. Health check

    Configuration Item Description Example
    Health Check Whether to enable or disable health check. In TCP listeners, CLB instances send SYN packets to specified server ports to perform health checks. Enabled
    Check Protocol To be added. To be added
    Check Port To be added. To be added
    Response Timeout
  • Maximum response timeout period for health check.
  • If a real server fails to respond within the timeout period, it is considered as unhealthy.
  • Value range: 2-60 seconds. Default value: 2s.
  • 2s
    Check Interval
  • Interval between two health checks.
  • Value range: 5-300 seconds. Default value: 5s.
  • 5s
    Unhealthy Threshold
  • If the health check returns failure for n consecutive times (n is user-defined), the real server is unhealthy and the unhealthy status is displayed in the console.
  • Value range: 2-10 times. Default value: 3 times
  • 3 times
    Healthy Threshold
  • If the health check returns success for n consecutive times (n is user-defined), the real server is healthy and the healthy status is displayed in the console.
  • Value range: 2-10 times. Default value: 3 times.
  • 3 times

    Complete the health check configuration as shown below:

    Step 3. Bind a real server

    Click Bind on the Listener Management page and select the real server to be bound in the pop-up window, as shown below:

    The configuration is as shown below:


    If you configure multiple listeners to a classic CLB instance and bind multiple real servers, each listener will forward requests to all real servers based on its configuration.

    Step 4. Security group (optional)

    You can configure a CLB security group to isolate public network traffic. For more information, see Configuring a CLB Security Group.

    Step 5. Modify or delete a listener (optional)

    If you need to modify or delete an existing listener, select the listener on the Listener Management page and click Modify or Delete.

    Contact Us

    Contact our sales team or business advisors to help your business.

    Technical Support

    Open a ticket if you're looking for further assistance. Our Ticket is 7x24 avaliable.

    7x24 Phone Support