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.
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. |
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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
Backend Server Group Type | Backend Server Type | Example |
|---|---|---|
Hybrid |
| As shown in Figure 1:
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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.
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.
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Load Balancing Algorithm | A load balancer distributes incoming traffic across backend servers based on the load balancing algorithm configured for the backend server group. For details about the comparison between different load balancing algorithms, see Table 4. | ||
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. For details about the comparison between different sticky session types, see Table 5. | ||
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. | ||
Load Balancing Algorithm | Description |
|---|---|
Weighted round robin | Requests are routed to backend servers in sequence based on their weights. Backend servers with higher weights receive proportionately more requests, whereas equal-weighted servers receive the same number of requests. |
Weighted least connections | In addition to the number of active connections established with each backend server, each server is assigned a weight based on its processing capability. Requests are routed to the server with the lowest connections-to-weight ratio. |
Consistent hashing
| Calculates the request fields using the consistent hashing algorithm to obtain a hash value and routes requests with the same hash value to the same backend server, even if the number of backend servers in the backend server group changes.
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Sticky Session Type | Description | Stickiness Duration (Minutes) | Scenarios Where Sticky Session Become Invalid |
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Source IP address | The source IP address of each request is calculated using the consistent hashing algorithm to obtain a unique hashing key, and all backend servers are numbered. The system allocates the requests from a client to a particular server based on the generated key. This allows requests from the same IP address to be forwarded to the same backend server. |
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Load balancer cookie | The load balancer generates a cookie after it receives a request from a client. All the subsequent requests with the same cookie are distributed to the same backend server. |
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Application cookie | The application deployed on the backend server generates a cookie after receiving the first request from the client. All subsequent requests with the cookie are routed to the same backend server. |
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 6.
Load Balancer Specification | Frontend Protocol | Backend Protocol |
|---|---|---|
Network load balancing | TCP | TCP |
Network load balancing | UDP |
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Network load balancing | TLS |
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Application load balancing | HTTP | HTTP |
Application load balancing | HTTPS |
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Application load balancing | QUIC |
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Helpful Links
- Creating a Backend Server Group
- Configuring Load Balancing Algorithms to Distribute Traffic
- Enabling Sticky Session to Accelerate Access
- Configuring Slow Start for a Backend Server Group
- Adding Backend Servers in the Same VPC as a Load Balancer
- Adding Backend Servers in a Different VPC from a Load Balancer