iTP Secure WebServer System Administrators Guide (Version 7.5+)

9 Using the Resource Locator Service (RLS)
The Resource Locator Service (RLS) is an optional feature that causes multiple Web servers to
appear to users as a single server. For example, an iTP Secure WebServer on a NonStop system
and a different Web server on a Windows NT platform could be used interchangeably for access
to the same content. For a given request, RLS selects which Web server to use. The selection criteria
are:
• Which Web server has demonstrated the best response time recently.
• Whether that Web server is available and not busy. (If the best-performing Web server is
currently unavailable or busy, RLS chooses the next-best Web server.)
By using RLS, you can implement replicated servers. The person or application that makes the
request cannot tell which Web server returned the reply or whether a particular Web server was
available.
RLS requires NonStop SQL/MP to be installed and running on the same system as RLS. Use a H01
or later version of NonStop SQL/MP.
The topics discussed in this section include:
• “Resource Locator Service (RLS) Architecture” (page 166)
• “Configuring the Resource Locator Service (RLS)” (page 166)
• “Building and Installing the Resource Locator Service (RLS)” (page 169)
Resource Locator Service (RLS) Architecture
RLS is implemented as a Pathway CGI server class. The interaction between RLS and other iTP
Secure WebServer components:
• The Distributor process receives a request from the network.
• The Distributor process sends the request to an httpd process.
• The httpd process determines whether it can service the request.
• If the httpd process can service the request, it does so without invoking RLS (in which case,
the other steps in this list do not apply). If the httpd process cannot service the request, it
invokes RLS, using the NonStop TS/MP Pathsend facility.
• RLS uses its SQL database to identify the set of Web servers that can handle the request.
• RLS attempts to connect to the best-performing Web server in the set, using TCP/IP if that server
is on a remote system. If the best-performing server is not available, RLS connects with the
next-best server.
• RLS stores response-time information from the server for use in subsequent decision-making.
Configuring the Resource Locator Service (RLS)
This subsection describes configuring RLS, including these tasks:
• “Defining the Server Class” (page 167)
• “Creating the Database” (page 167)
• “Modifying the Database” (page 169)
CAUTION: RLS does not verify that the servers you define can actually provide access to the
same content and services. You (or your website administrator) must check that each replicated
server has the same or similar features and configuration.
166 Using the Resource Locator Service (RLS)