Indirect-mode server load balancing
Figure 45: Network diagram
As shown in Figure 45, indirect-mode server load balancing contains the following elements:
Cluster—A cluster contains an LB device, a general device, and multiple servers to provide services.
LB device—Distributes different service requests to multiple servers.
General device—Forwards data according to general forwarding rules.
Server—Responds to and processes different service requests.
VSIP—Virtual service IP address of the cluster, used for users to request services.
Server IP—IP address of a server, used by the LB device to distribute requests.
Indirect-mode server load balancing requires configuring the VSIP on both the LB device and the servers. Because the VSIP on a server cannot be contained in an ARP request and response, you can configure the VSIP on a loopback interface.
Figure 46: Indirect-mode server load balancing workflow
Table 12: Workflow description
Description | Source IP address | Destination IP address |
|---|---|---|
1. The host sends a request. | Host IP | VSIP |
2. When the general device receives the request, it forwards it to LB device. The VSIP cannot be contained in an ARP request and response, so the general device only forwards the request to the LB device. | Host IP | VSIP |
3. When the LB device receives the request, it uses a scheduling algorithm to calculate to which server it distributes the request. | N/A | N/A |
4. The LB device distributes the request. The source and destination IP addresses in the request packet are not changed. | Host IP | VSIP |
5. The server receives and processes the request and then sends a response. | VSIP | Host IP |
6. The general device receives the response, and forwards it to the requesting host. | VSIP | Host IP |
In indirect mode, the LB device does not forward packets returned by the server.