Classic CLB is easy to configure and supports simple load balancing scenarios:
CLB offers two types of instances: CLB (formerly "application CLB") and classic CLB.
CLB has all features of classic CLB. Given their product features and performance, we recommend that you use CLB. For a detailed comparison, see Instance Types.
This document gives an overview of classic CLB instances. After creating an instance, you need to configure a listener to it. The listener listens to requests on the instance and routes traffic to the real server based on the balancing policy.
You need to configure the following for a CLB listener:
If you configure multiple listeners to a classic CLB instance and bind multiple real servers, each listener will route requests to all real servers according to its own configuration.
A CLB listener can listen to layer-4 and layer-7 requests on a CLB instance and route them to the real server for processing. The main difference between layer-4 CLB and layer-7 CLB lies in that the former routes traffic for load balancing of user requests based on the layer-4 protocols, while the latter on the layer-7 protocols.
- A classic CLB instance mainly receives requests and routes traffic to the real server via VIP and port, as layer-7 protocols do not support traffic routing based on domain name and URL.
- A private network classic CLB instance supports only layer-4 protocols but not layer-7 protocols.
- If you need the above advanced functions, we recommend choosing CLB over classic CLB. For more information, see Instance Types.
|Listening port (frontend port)||Service port (backend port)||Description|
|Via the listening port, a CLB instance receives and routes requests to the real server for load balancing.
You can configure CLB instances for port 1 to 65535, such as 21 (FTP), 25 (SMTP), 80 (HTTP), and 443 (HTTPS).
|A service port receives the traffic from the CLB instance.
On a CLB instance, one listening port can route traffic to multiple ports of multiple CVM instances.
For example, `TCP:80` and `HTTP:80` listeners cannot co-exist.
For example, you can create `TCP:80` and `UDP:80` listeners at the same time.
There can be multiple service ports on a CLB instance.
For example, both `HTTP:80` and `HTTPS:443` listeners can be bound to the same port of a CVM instance.