This topic introduces the terms used in Classic Load Balancer (CLB).
|CLB||CLB is a network load balancing service of Alibaba Cloud that provides Layer 4 and Layer 7 load balancing capabilities. CLB can distribute traffic across multiple Elastic Compute Service (ECS) instances in one or more zones.|
|CLB instance||A CLB instance is a load balancing instance in Alibaba Cloud. To get started with CLB, you must create a CLB instance.|
|Endpoint||An endpoint is an IP address assigned to a CLB instance. CLB instances can have public and private IP addresses based on the type of instance created. You can resolve a domain name to the public IP address of a CLB instance to provide services over the Internet.|
|Listener||A listener determines how CLB routes requests to backend servers. At least one listener must be added to a CLB instance.|
|Backend server||A backend server is an ECS instance that receives client requests distributed by a CLB instance.|
|Default server group||
The default server group is a group of ECS instances that process the requests routed by listeners that are not configured with a vServer group or primary/secondary server group.
A vServer group is a group of ECS instances that process requests routed from listeners.
You can create multiple vServer groups for different listeners of a CLB instance. This way, the listeners can forward traffic to the ECS instances in different vServer groups.
|Primary/Secondary server group||A primary/secondary server group is a server group that contains two ECS instances. One instance functions as the primary server and the other instance functions as the secondary server. If the primary server is detected unhealthy, new requests are automatically routed to the secondary server.|