Nortel Networks WEB OS 212777 - Manual (Page 122)

Web OS 10.0 Application Guide
122 n Chapter 6: Server Load Balancing
212777-A, February 2002
All of the above issues can be addressed by adding an Alteon Web switch with SLB software.
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Reliability is increased by providing multiple paths from the clients to the Web switch and
by accessing a pool of servers with identical content. If one server fails, the others can take
up the additional load.
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Performance is improved by balancing the Web request load across multiple servers. More
servers can be added at any time to increase processing power.
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For ease of maintenance, servers can be added or removed dynamically, without interrupt-
ing shared services.
Network Topology Requirements
When deploying SLB, there are a few key aspects to consider:
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In standard SLB, all client requests to a virtual server IP address and all responses from the
real servers must pass through the switch, as shown in
Figure 6-4 . If there is a path between
the client and the real servers that does not pass through the switch, the Web switch can be
configured to proxy requests in order to guarantee that responses use the correct path (see
“Proxy IP Addresses” on page 136 ).
Figure 6-4 SLB Client/Server Traffic Routing
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Identical content must be available to each server in the same pool. Either of these meth-
ods can be used:
o Static applications and data are duplicated on each real server in the pool.
o Each real server in the pool has access to the same data through use of a shared file
system or back-end database server.
Clients
Switch
Internet NFS Server
Server Pool #1
Server Pool #2
Switch
Alternate path is not valid with
Layer 4 services. IP proxy
addresses must be used on the
Alteon Web switch
Web
Switch
Router
Router