Cisco Explorer 4700 Installation Guide download pdf (Page 236)

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Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance

OL-26645-02

Chapter 6 Configuring Real Servers and Server Farms

Configuring Server Farms

Least Loaded The ACE selects the server with the lowest load based on information from SNMP probes.

1. In the SNMP Probe Name field, select the name of the SNMP probe to use.

2. In the Auto Adjust field, configure the autoadjust feature to instruct the ACE to apply the

maximum load of 16000 to a real server whose load reaches zero or override the default

behavior. By default, the ACE applies the average load of the server farm to a real server

whose load is zero. The ACE periodically adjusts this load value based on feedback from the

server SNMP probe and other configured options.

Options are as follows:

–

Average—Applies the average load of the server farm to a real server whose load is zero.

This setting allows the server to participate in load balancing, while preventing it from

being flooded by new connections. This is the default setting.

–

Maxload—Instruct the ACE to apply the maximum load of 16000 to a real server whose

load reaches zero.

–

Off—Instruct the ACE to send all new connections to the server that has a load of zero

until the next load update arrives from the SNMP probe for this server. If two servers have

the same lowest load (either zero or nonzero), the ACE load balances the connections

between the two servers in a round-robin manner.

3. In the Weight Connection field, check the check box to instruct the ACE to use the current

connection count in the final load calculation for a real server. When you configure this

option, the ACE includes the current connection count in the total load calculation for each

real server in a server farm. Clear the check box to reset the behavior of the ACE to the default

of excluding the current connection count from the load calculation.

To instruct the ACE to select the server with the lowest load, use the predictor least-loaded

command in server farm host or redirect configuration mode. With this predictor, the ACE uses

SNMP probes to query the real servers for load parameter values (for example, CPU utilization or

memory utilization). This predictor is considered adaptive because the ACE continuously provides

feedback to the load-balancing algorithm based on the behavior of the real server.

To use this predictor, you must associate an SNMP probe with it. The ACE queries user-specified

OIDs periodically based on a configurable time interval. The ACE uses the retrieved SNMP load

value to determine the server with the lowest load.

The syntax of this predictor command is as follows:

predictor least-loaded probe name

The name argument specifies the identifier of the existing SNMP probe that you want the ACE to

use to query the server. Enter an unquoted text string with no spaces and a maximum of

64 alphanumeric characters.

For example, to configure the ACE to select the real server with the lowest load based on feedback

from an SNMP probe called PROBE_SNMP, enter:

host1/Admin(config)# serverfarm SF1

host1/Admin(config-sfarm-host)#

predictor least-loaded probe PROBE_SNMP

host1/Admin(config-sfarm-host-predictor)#

To reset the predictor method to the default of Round Robin, enter:

host1/Admin(config-sfarm-host)# no predictor

Table 6-7 Predictor Method Attributes (continued)

Predictor Method Description / Action

1 ... 235 236 237 ... 648

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