iTP Secure WebServer System Administrator's Guide (iTPWebSvr 6.0+)

iTP Secure WebServer System Administrator’s Guide—523346-002
10-1
10
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 an 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 D43 or later version of NonStop SQL/MP.
The topics discussed in this section include”
•
Resource Locator Service (RLS) Architecture on page 10-1
•
Configuring the Resource Locator Service (RLS) on page 10-2
•
Building and Installing the Resource Locator Service (RLS) on page 10-6
Resource Locator Service (RLS) Architecture
RLS is implemented as a Pathway CGI server class. The interaction between RLS and
other iTP Secure WebServer components is as follows:
1. The Distributor process receives a request from the network.
2. The Distributor process sends the request to an httpd process.
3. The httpd process determines whether it can service the request.
4. If the httpd process can service the request, it does so without invoking RLS (in
which case, the other steps in this list don’t apply). If the httpd process cannot
service the request, it invokes RLS, using the NonStop TS/MP Pathsend facility.
5. RLS uses its SQL database to identify the set of web servers that can handle the
request.
6. 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.