Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 29)

Brocade Virtual ADX Server Load Balancing Guide 13
53-1003247-01
Overview
2
Dynamic weighted predictor
The Brocade Virtual ADX provides a dynamic weighted predictor that enables it to make load
balancing decisions using real time server resource usage information, such as CPU utilization and
memory consumption. The Brocade Virtual ADX retrieves this information (through the SNMP
protocol) from MIBs available on the application servers.
To achieve this capability, a software process in the Brocade Virtual ADX, named SNMP manager
(also called SNMP client) is used. This process is different from the SNMP agent process (a.k.a.
SNMP server process) on the Brocade Virtual ADX. A Brocade Virtual ADX can be configured as
both SNMP agent (that allows management of the Brocade Virtual ADX through Network
Management System), and SNMP manager (that facilitates the new SNMP based predictor
method). In addition, all the real servers must run the SNMP agent daemon and support MIBs that
can be queried by the SNMP manager of the Brocade Virtual ADX.
You can fine-tune how traffic is distributed across these real servers by enabling Dynamic Weighted
Predictor on the Brocade Virtual ADX.
The Dynamic Weighted predictors can be applied globally to apply for the entire Brocade Virtual
ADX or locally per virtual server as described in
“Changing the Load-Balancing Predictor Method”
on page 21 and “Configuring dynamic weighted predictor” on page 24.
NOTE
The global command snmp-server is enabled by default and this command must not be removed if
the dynamic weighted predictor is configured. If this command is removed, then the Brocade Virtual
ADX will stop listening on the UDP port 161 and drop SNMP responses from the real servers that are
used for this predictor.
Dynamic-weighted Direct
The SNMP response from each server is regarded as a performance weight. The displayed SNMP
Weight under “show server real” is the direct weight from the SNMP response. Weighted load
balancing is similar to least connections, except that servers with a higher weight value receive a
larger percentage of connections at a time. The dynamic weight is polled for the specified real
server, and that weight determines the percentage of the current connections that are given to the
server. The default weight is 0 if it does not receive any SNMP response.
For example, in a configuration with five servers of various weights, the percentage of connections
is calculated as follows:
• Weight server1 = 7
• Weight server2 = 8
• Weight server3 = 2
• Weight server4 = 2
• Weight server5 = 5
• Total weight of all servers = 24
The result is that Server1 gets 7/24 of the current number of connections, Server2 gets 8/24,
Server3 gets 2/24, and so on. If a new server, Server6, is added with a weight of 10, the new server
gets 10/34.