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

You need to configure a CLB listener with the following items:

1. Listening protocol and port. The listening port, or frontend port, is used to receive and forward requests to real servers.
2. Listening policies, such as load balancing policy and session persistence.
3. Health check policies.
4. Real server. Bind a real server by selecting its IP and port. A service port, or backend port, is used by the real server to receive requests.

Supported Protocol Types

A CLB listener can listen to layer-4 and layer-7 requests on a CLB instance and route them to real servers for processing. The main difference between layer-4 CLB and layer-7 CLB is whether layer-4 or layer-7 protocol is used to forward traffic for load balancing of user requests.

• Layer-4 protocols: transport layer protocols that receive requests and forward traffic to the real server mainly via VIP and port.
• Layer-7 protocols: application layer protocols that distribute traffic based on application layer information such as URL and HTTP header.

If you use a layer-4 listener (i.e., layer-4 protocol forwarding), the CLB instance will establish a TCP connection with the real server on the listening port, and directly forward requests to the real server. This process does not modify any data packets (in pass-through mode) and has high forwarding efficiency.

Tencent Cloud CLB supports request forwarding over the following protocols:

• TCP (transport layer)
• UDP (transport layer)
• TCP SSL (transport layer)
• HTTP (application layer)
• HTTPS (application layer)

Note：

TCP SSL listeners currently support public network CLB instances but not private network or classic CLB instances.

Port Configuration