Installation guide

CHAPTER 4 Installing and Configuring a Web Server Redirector Plug-In
Installation Guide 39
Figure 4-1: HTTP request flow through the redirector
Load balancing
Load balancing is transparent to the client. The redirector detects and directs
requests from existing sessions to EAServer using either the J2EE cookie or the
J2EE session identifier that is part of the HTTP request.
If the cookie or identifier is missing, the client is treated as a new client,
otherwise, the redirector sends the request to the EAServer that originally
established the session.
New requests are directed to different application servers that share and
balance the load. Load balancing is based on a round-robin scheme. If a
redirector is configured to service n number of application servers, and a new
request arrives at the redirector, it is directed to the next application server in
its list (as defined by the redirector configuration file) that has not previously
serviced a request. The next new request is sent to the next available server, and
so on.
Apache Web server
Apache Web servers handle load balancing differently than iPlanet. Apache
Web servers spawn multiple processes to handle the client load, whereas the
other Web servers use only a single process. Since Apache spawns multiple
processes, client request loads are balanced for each Apache Web server
process, not for all Apache processes. Therefore, while monitoring connection
requests from an Apache Web server to multiple EAServer installations, you
might initially see many new client requests from multiple Apache processes
being directed to a single EAServer. In time, and as the number of client
requests to the Apache Web server increases, the load is evenly distributed
across all EAServer installations.