Configuring a Load-Balancing Predictor
This chapter describes how to configure a load-balancing predictor on the Cisco 4700 Series Application Control Engine (ACE) appliance. This chapter contains the following sections:
•Configuring a Hash Header Predictor Using the Device Manager GUI
•Configuring a Hash Header Predictor Using the CLI
After reading this chapter, 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:
Step 1 Choose a server farm.
Step 2 Choose a predictor type and its parameters.
Step 3 Deploy the configuration.
This chapter describes how to configure a hash header predictor for the server farm that was created in Chapter 6, "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:
Step 1 Choose Config > Virtual Contexts. Choose context VC_web.
Step 2 Choose Load Balancing > Server Farms. The Server Farms pane appears (Figure 7-1).
Figure 7-1 Configuring a Predictor
Step 3 Choose SF_web.
Step 4 Choose the Predictor tab.
Step 5 Choose Hash_Header for the predictor Type.
Step 6 Choose Accept for the Header Name.
Step 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:
Step 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
Step 2 Enter configuration mode for SF_web.
host1/VC_web(config)# serverfarm SF_web
Step 3 Configure a hash header predictor.
host1/VC_web(config-sfarm-host)# predictor hash header Accept
Step 4 Display the predictor configuration information.
host1/VC_web# show running-config serverfarm
In this chapter, you have configured a hash header predictor for your server load balancing. Next, you will configure server persistence by using the stickiness feature.