Implementation Guide › Performance Tuning › Web Tier Performance › Web Server Performance › Web Servers, Web Agents, and Web Server Processes › Web Agent and Policy Server Interaction using Apache-based Web Server Pre-Fork Mode

Web Agent and Policy Server Interaction using Apache-based Web Server Pre-Fork Mode

When an Apache-based web server in pre-fork mode receives a request, the web server spawns a child process to communicate with the SiteMinder Policy Server. When more requests are received, more child-processes are spawned to handle them. Each child process spawned by the Apache-based web server has its own independent connections to the SiteMinder Policy Server.

The following illustration describes this process:

For Apache-based web servers, the value of the MaxClients parameter (in the httpd.conf file) determines the number of child processes spawned the web server. When a parent process from an Apache-based web server spawns a child process, the child process opens an initial connection to the SiteMinder Policy Server.

An important distinction exists between the number of Web Agents, and the number of Web Agent processes. Each Web Agent requires its own web server instance. IIS web servers, for example, only operate as a single instance, so the number of IIS Web Agents equals the number of IIS web servers. For other types of servers, it is possible to have multiple server instances listening on different ports within one physical web server.

The maximum number of sockets opened from an Apache-based web server to a SiteMinder Policy Server equals the value of the MaxClients parameter multiplied by the number of Web Agent processes. For example, if the value of the MaxClients parameter of your server is set to 150, and you have five Web Agent processes, then the maximum number of possible sockets opened is 750.

Using a multiprocess web server affects the ratio of Web Agent processes to Policy Servers in your SiteMinder environment. The limiting factor often becomes the number of connections between the Web Agent processes and the Policy Server, not the number of transactions per second.

Before deploying Web Agents, verify that the SiteMinder Policy Servers receiving the requests can handle the maximum number of connections that the related web servers could open.