Help Center/ Elastic Load Balance/ User Guide/ User Guide for Dedicated Load Balancers/ Backend Server Group/ Backend Server Group Overview
Updated on 2026-07-09 GMT+08:00
View PDF

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. A backend server can be a cloud server, supplementary network interface, or IP address.

The following table describes how a backend server group works in the traffic forwarding process.

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.

For dedicated load balancers, the backend server group type can be Hybrid or IP as a backend server. You can add cloud servers, supplementary network interfaces, or IP addresses to a hybrid backend server group. If you set the type to IP as a backend server, you can only add IP addresses as backend servers.

Figure 1 shows the architecture of different types of backend server groups. For details, see Table 2.

Figure 1 Backend server group architecture
Table 2 Backend server group types

Backend Server Group Type

Backend Server Type

Example

Hybrid
  • Cloud servers and supplementary network interfaces that are in the same VPC as the load balancer
  • Cloud servers in other VPCs or on-premises servers if IP as a backend is enabled for the load balancer

As shown in Figure 1:

  • In backend server group A, you can add ECSs or supplementary network interfaces in VPC1.
  • In backend server group B, you can add IP addresses in VPC2 as backend servers.

IP as a backend server

IP addresses of cloud or on-premises servers if IP as a backend is enabled for the load balancer

As shown in Figure 1, IP addresses can be added to backend server group C as backend 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 time. This can help avoid low resource utilization and make it easier to manage backend servers.
  • Higher reliability: The health check function ensures 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

Forwarding Mode

Specifies the forwarding mode used by the load balancer to distribute traffic.

There are two options: Load balancing and Active/Standby.

  • Load balancing: Multiple backend servers can be added to this type of backend server group. The load balancer distributes requests across these backend servers based on the load balancing algorithm configured for this backend server group.
  • Active/Standby: After the active and standby nodes are configured, the load balancer distributes traffic based on the health check results of the active and standby nodes. The roles of the active and standby nodes are not switched. The following shows how this works:
    • If the active node is healthy, the load balancer forwards traffic to the active node.
    • If the active node is unhealthy but the standby node is healthy, new connections will be established with the standby node, and the existing connections with the active node are disconnected after the timeout interval expires.
    • When the active node becomes healthy, new connections will be established with the active node again, and the existing connections with the standby node are disconnected after the timeout interval expires.

Creating a Backend Server Group

Load Balancing Algorithm

Specifies the algorithm used by the load balancer to distribute traffic.

Configuring Load Balancing Algorithms to Distribute Traffic

Sticky Session

Specifies whether to enable the sticky session option. If you enable this option, all requests from the same client during one session are sent to the same backend server.

Enabling Sticky Session to Accelerate Access

Slow Start

Specifies whether to enable slow start. After you enable it, the load balancer linearly increases the proportion of requests to new backend servers in the backend server group.

When the slow start duration elapses, the load balancer sends full share of requests to these backend servers and exits the slow start mode.

Configuring Slow Start for a Backend Server Group

Forward to Same Port

Specifies whether to enable the forward to same port option. After you enable it, you do not need to specify a backend port when you add a backend server. The listener routes the requests to the backend server over the same port as the frontend port.

Creating a Backend Server Group

Backend Server Group and Listener Protocols

You can associate a backend server group with different dedicated load balancers under the same enterprise project or different listeners.

The backend protocol of the new backend server group must match the frontend protocol of the listener, as described in Table 4.

Table 4 The frontend and backend protocols

Load Balancer Specification

Frontend Protocol

Backend Protocol

Network load balancing

TCP

TCP

Network load balancing

UDP
  • UDP
  • QUIC

Application load balancing

HTTP

HTTP

Application load balancing

HTTPS
  • HTTP
  • HTTPS
  • gRPC

Helpful Links

Parent Topic: Backend Server Group