After you create a CLB instance, you need to configure a listener for the instance. The listener is responsible for monitoring requests on the CLB instance and distributing traffic to the backend servers based on the balancing policy.
The CLB listener needs to be configured:
- Listening protocol and listening port. The listening port of the CLB, also known as the frontend port, is the port used to receive requests and forward requests to the backend server.
- Monitoring policies, including balancing policies, session persistence, etc.
- Health Check policies.
- Bind the backend service and select the IP and port of the backend server. The service port is also called the backend port, which is the port used to receive requests.
Supported Protocol Types
The CLB listener can listen to the layer-4 and layer-7 requests on the CLB instance and distribute these requests to the backend servers, which then process the requests. The difference between layer-4 and layer-7 load balancing is mainly reflected in whether the traffic is forwarded based on the layer-4 protocol or the layer-7 protocol when the CLB user requests.
- Layer-4 Protocol: Transport layer protocol, which mainly accepts requests through VIP + Port and distributes traffic to the backend server.
- Layer-7 Protocol: Application layer protocol, which distributes traffic based on application layer information such as URL and HTTP header.
Converge Cloud CLB supports request forwarding of the following protocols: - TCP (transport layer)
- UDP (transport layer)
- HTTP (application layer)
- HTTPS (application layer)
Layer-4 listener
| Protocols | Note | Use Cases |
|---|---|---|
| TCP | Connection-Oriented, Reliable Transport Layer Protocol - The source and terminal of the transmission need to be handshake three times to establish a connection before data transmission. - Support session persistence based on client IP (source IP). - You can see the client IP at the network layer. - The server can directly obtain the client IP. |
It is suitable for cases with high requirements on reliability and data accuracy but low requirements on transmission speed, such as file transfer, email sending and receiving, remote log-in, etc. For details, see Configuring TCP Listener. |
| UDP | Connectionless Transport Layer Protocol - The transmission source and terminal do not establish a connection, and there is no need to maintain the connection status. - Each UDP connection can only be point-to-point. - Supports one-to-one, one-to-many, many-to-one and many-to-many interactive communications. - Support session persistence based on client IP (source IP). - The server can directly obtain the client IP. |
It is suitable for cases with high requirements on transmission efficiency and relatively low requirements on accuracy, such as instant messaging and online videos. For details, see Configuring UDP Listener. |
If you use a layer-4 listener (that is, use layer-4 protocol forwarding), the CLB instance establishes a TCP connection with the backend instance on the listening port and directly forwards the request to the backend server. No data packets are modified during this process (transparent transmission mode), and the forwarding efficiency is extremely high.
Layer-7 Listener
| Protocols | Note | Use Cases |
|---|---|---|
| HTTP | Application Layer Protocol - Supports forwarding based on request domain name and URL. - Supports cookie-based session persistence. |
Applications that need to identify the content of requests, such as Web applications, App services. For details, see Configuring HTTP Listener. |
| HTTPS | Encrypted Application Layer Protocol - Supports forwarding based on request domain name and URL. - Supports cookie-based session persistence. - Unified certificate management service. CLB completes decryption operations. - Supports single authentication and two-way authentication. |
HTTP applications that require encrypted transmission. For details, see Configuring HTTPS Listener. |
Port Configuration
| Listening port (frontend port) | Service port (backend port) | Note |
|---|---|---|
| The port on which the CLB is provided receives requests and forwards them to the backend server. Users can configure load balancing for ports 1 - 65,535, including 21 (FTP), 25 (SMTP), 80 (HTTP), 443 (HTTPS), etc. |
The service port is the port that provides services for the CVM and receives and processes traffic from the CLB. In a CLB instance, the same CLB listening port can forward traffic to multiple ports of multiple CVMs. |
In the same CLB instance: The listening port cannot be repeated. For example, you cannot create a listener TCP:80 and a listener HTTP:80 at the same time. Only ports for TCP and UDP protocols can be repeated. For example, you can create a listener for TCP:80 and a listener for UDP:80 at the same time. Service ports can be repeated within the same CLB instance. For example, the listener HTTP:80 and the listener HTTPS:443 can be bound to the same port of the same CVM at the same time. |