Table Of Contents

Configuring a Load-Balancing Predictor

Information About Load-Balancing Predictors

Configuring the Round-Robin Predictor

Configuration Example for the Hash Header Predictor

Where to Go Next

Configuring a Load-Balancing Predictor

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This chapter describes how to configure a load-balancing predictor (method) on the Cisco Application Control Engine (ACE) module.

This chapter contains the following sections:

•Information About Load-Balancing Predictors

•Configuring the Round-Robin Predictor

•Configuration Example for the Hash Header Predictor

•Where to Go Next

Information About Load-Balancing Predictors

After reading this chapter, you should have a basic understanding of how the ACE selects a real server for a client request using a predictor and how to configure the round-robin and the least-connections predictors.

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 the 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 type is the default predictor.

•Least connections— Selects the server with the fewest number of connections based on the server weight. This predictor is useful for processing light user requests (for example, browsing simple static web pages). Use the optional slow-start mechanism to avoid sending a high rate of new connections to servers that you have recently put into service. When a new real server enters slow-start mode, the ACE calculates and assigns an artificially high metric weight value to the new server and sends a small number of connections to the new server initially. The remaining connections go to the existing servers based on their weight and current connections. When the slow-start timer expires or the real server weight reaches zero, the ACE takes the server out of slow-start mode and assigns connections normally.

For a complete list of predictor types that the ACE supports and how to configure them, see the Cisco Application Control Engine Module Administration Guide.

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 shown in Figure 6-1.

Configuring the Round-Robin Predictor

Procedure

	Command	Purpose
Step 1	changeto context Example: host1/Admin# changeto VC_WEB host1/VC_WEB#	Changes to the correct context if necessary. Check the CLI prompt to verify that you are operating in the desired context.
Step 2	config Example: host1/VC_WEB# config host1/VC_WEB(config)#	Enters configuration mode.
Step 3	serverfarm name Example: host1/VC_WEB(config)# serverfarm SF_WEB host1/VC_WEB(config-sfarm-host)#	Enters server farm host configuration mode for SF_WEB.
Step 4	predictor roundrobin Example: host1/VC_WEB(config-sfarm-host)# predictor roundrobin	Configures the round-robin predictor. For weighted round-robin, assign a weight to the real server.
Step 5	exit Example: host1/VC_WEB(config-sfarm-host)# exit host1/VC_WEB(config)# exit host1/VC_WEB#	Exits server farm host configuration mode. Exits configuration mode.
Step 6	show running-config serverfarm Example: host1/VC_WEB# show running-config serverfarm	Display the predictor configuration information.
Step 7	copy running-config startup-config Example: host1/VC_WEB# copy running-config startup-config	(Optional) Copies the running configuration to the startup configuration.

Configuration Example for the Hash Header Predictor

The following example shows how to configure the hash header predictor. The commands that you have configured in this chapter appear in bold text.

switch/VC_WEB(config)# do show running config

Generating configuration....

access-list INBOUND line 8 extended permit ip any any

rserver host RS_WEB1

  description content server web-one

  ip address 10.10.50.10

  inservice

rserver host RS_WEB2

  description content server web-two

  ip address 10.10.50.11

  inservice

rserver host RS_WEB3

  description content server web-three

  ip address 10.10.50.12

  inservice

rserver host RS_WEB4

  description content server web-four

  ip address 10.10.50.13

  inservice

serverfarm host SF_WEB

  predictor roundrobin

  rserver RS_WEB1 80

    inservice

  rserver RS_WEB2 80

    inservice

  rserver RS_WEB3 80

    inservice

  rserver RS_WEB4 80

    inservice

class-map type management match-any REMOTE_ACCESS

  description Remote access traffic match

  2 match protocol ssh any

  3 match protocol telnet any

  4 match protocol icmp any

class-map match-all VS_WEB

  2 match virtual-address 10.10.40.10 tcp eq www

policy-map type management first-match REMOTE_MGMT_ALLOW_POLICY

  class REMOTE_ACCESS

    permit

policy-map type loadbalance first-match PM_LB

  class class-default

    serverfarm SF_WEB

policy-map multi-match PM_MULTI_MATCH

  class VS_WEB

    loadbalance vip inservice

    loadbalance policy PM_LB

service-policy input REMOTE_MGMT_ALLOW_POLICY

interface vlan 400

  description Client connectivity on VLAN 400

  ip address 10.10.40.1 255.255.255.0

  access-group input INBOUND

  service-policy input PM_MULTI_MATCH

  no shutdown

interface vlan 500

  description Server connectivity on VLAN 500

  ip address 10.10.50.2 255.255.255.0

  no shutdown

domain DOMAIN1

add-object all

ip route 0.0.0.0 0.0.0.0 172.25.91.1

username USER1 password 5 $1$vAN9gQDI$MmbmjQgJPj45lxbtzXPpB1  role SLB-Admin domain 
DOMAIN1

Where to Go Next

In this chapter, you have configured a hash header predictor for your server load balancing. In the next chapter, you will configure server persistence by using the stickiness feature.