Cisco ACE 4700 Series Appliance Quick Start Guide, Release A3(1.0) -- Configuring a Load-Balancing Predictor
This section describes how to configure a load-balancing predictor on the Cisco 4700 Series Application Control Engine (ACE) appliance.
After reading this section, you should have a basic understanding of how the ACE appliance selects a real server for a client request using a predictor and how to configure a hash header predictor as an example.
When there is a client request for web services, the ACE selects a server that can successfully fulfill the client request in the shortest amount of time without overloading either the individual server or the server farm.
The ACE makes load-balancing choices using a predictor. When you configure a predictor, you define the series of checks and calculations that the ACE will perform to determine which real server can best service a client request.
For each server farm, you can configure one of several predictor types to allow the ACE to select an appropriate server. Two common predictor types include the following:
- Round-robin—Selects a server from the list of real servers based on weighted server capacity. A weight can be assigned to each real server based on its connection capacity in relation to the other servers in a server farm. Servers with higher weight values receive a proportionally higher number of connections than servers with lower weight values. For example, a server with a weight of 5 would receive five connections for every one connection received by a server with a weight of 1. Also known as weighted round-robin, this is the default predictor.
- Hash header—Selects a server using a hash value based on the HTTP header name.
For a complete list of predictor types that the ACE supports and how to configure them, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.
You can configure a server load-balancing predictor by following these steps:
1. Choose a server farm.
2. Choose a predictor type and its parameters.
3. Deploy the configuration.
This section describes how to configure a hash header predictor for the server farm that was created in Configuring Server Load Balancing (as illustrated in Figure 6-1). You can use either the ACE Device Manager GUI or the CLI.
Configuring a Hash Header Predictor Using the Device Manager GUI
You can configure a hash header predictor using the ACE Device Manager GUI by following these steps:
1. Choose Config > Virtual Contexts. Choose context VC_web.
2. Choose Load Balancing > Server Farms. The Server Farms pane appears (Figure 1).
- Figure 1 Configuring a Predictor
3. Choose SF_web.
4. Choose the Predictor tab.
5. Choose Hash_Header for the predictor Type.
6. Choose Accept for the Header Name.
7. Assign the hash header predictor to server farm SF_web by clicking Deploy Now.
Configuring a Hash Header Predictor Using the CLI
You can configure a hash header predictor using the CLI by following these steps:
1. Verify that you are operating in the desired context by checking the CLI prompt. If necessary, change to the correct context.
- host1/Admin# changeto VC_web
2. Enter configuration mode for SF_web.
- host1/VC_web# config
- host1/VC_web(config)# serverfarm SF_web
3. Configure a hash header predictor.
- host1/VC_web(config-sfarm-host)# predictor hash header Accept
4. Display the predictor configuration information.
- host1/VC_web(config-sfarm-host)# exit
- host1/VC_web(config)# exit
- host1/VC_web# show running-config serverfarm
In this section, you have configured a hash header predictor for your server load balancing. Next, you will configure server persistence by using the stickiness feature.