Overview

Introduction

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 an ECS, BMS, or IP address.

The following process describes how a backend server group forwards traffic:

  1. A client sends a request to your application. The listeners added to your load balancer use the protocols and ports you have configured forward the request to the associated backend server group.

  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.

  3. In this way, massive concurrent requests can be processed at the same time, improving the availability of your applications.

Table 1 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.

Adding Backend Servers

IP as backend servers

You can add cloud servers in other VPCs or on-premises servers if IP as a backend is enabled for the load balancer.

Adding IP Addresses 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 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.

Key Functions

You can configure the key functions listed in Table 2 for each backend server group to ensure service stability.

Table 2 Key functions

Key Function

Description

Detail

Removal Protection

Specifies whether to enable the removal protection option to prevent a backend server group from being removed by accident.

Enabling Removal Protection for a Backend Server Group

Health Check

Specifies whether to enable the health check option. Health checks determine whether backend servers are healthy.

If a backend server is detected unhealthy, it will not receive requests from the associated load balancer, improving your service reliability.

Health Check

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

Slow Start

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

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

Note

Slow start is only available for HTTP and HTTPS backend server groups of dedicated load balancers.

Slow Start (Dedicated Load Balancers)

Precautions for Creating a Backend Server Group

The backend protocol of the new backend server group must match the frontend protocol of the listener as described in Table 3.

You can create a backend server group by referring to Table 4.

Table 3 The frontend and backend protocol

Frontend Protocol

Backend Protocol

TCP

TCP

UDP

  • UDP

  • QUIC

HTTP

HTTP

HTTPS

  • HTTP

  • HTTPS

Table 4 Creating a backend server group

Load Balancer Type

Reference

Dedicated

Creating a Backend Server Group (Dedicated Load Balancers)