Backend Server Group Overview

What Is a Backend Server Group?

A backend server group is a logical collection of one or more backend servers to receive massive concurrent requests at the same time. Only cloud servers can be added as backend servers.

The following table describes how a backend server group forwards traffic.

**Table 1** Traffic distribution process
Step 1	A client sends a request to your application. The listeners added to your load balancer use the protocols and ports you have configured to forward the request to the associated backend server group.
Step 2	Healthy backend servers in the backend server group receive the request based on the load balancing algorithm, handle the request, and return a result to the client.
Step 3	In this way, massive concurrent requests can be processed at the same time, improving the availability of your applications.

Shared load balancers have only one type of backend server group, where you can only add cloud servers.

**Table 2** Adding backend servers
Backend Server Type	Description	Reference
Cloud servers	You can add ECSs or BMSs that are in the same VPC as the load balancer.	Cloud Servers

Advantages

Backend server groups can bring the following benefits:

Reduced costs and easier management: You can add or remove backend servers as traffic changes over the time. This can help avoid low resource utilization and makes it easy to manage backend servers.
Higher reliability: Traffic is routed only to healthy backend servers in the backend server group.

Controlling Traffic Distribution

You can configure the key functions listed in Table 3 for each backend server group to ensure service stability.

**Table 3** Key functions
Key Function	Description		Detail
Load Balancing Algorithm	The load balancer distributes traffic based on the load balancing algorithm you have configured for the backend server group.		Load Balancing Algorithms
Sticky Session	Specifies whether to enable the sticky session option. If you enable this option, all requests from a client during one session are sent to the same backend server.		Sticky Session