MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION..., Manual

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Chapter 6: Creating Scalable and Highly Available Web Sites 145
Availability & reliability
In the simplest of terms, availability and reliability means you can access your Web site
whenever you request it by entering the site’s URL in your browser and all of its
features work as intended. Thus, availability and reliability refers to the uptime of a
Web site, which is often directly related to the uptime of the Web server and other
dependent servers, such as a database server, an application server, or a file server. All
of the servers that provide your site’s functionality must work for a site to be
considered available.
For ColdFusion applications, it’s particularly important that the ColdFusion Server
(CFS) remain as highly available and responsive as the Web server and other
dependent servers. The CFS processes application-specific logic that is sent to it from
the Web server by interpreting embedded CFML tags. Upon successfully processing
the application logic, the CFS returns the results back to the Web server, which in turn
returns an HTML response back to the browser. For all of this to occur correctly and
within acceptable time frames, the CFS itself must remain available and not become
overloaded. To that end, the scalability and high availability technology embedded in
ColdFusion ensures that your CFS is load balanced as well as your Web server.
Availability and reliability is concerned with keeping the relevant servers that provide
services to your Web application available at all times. However, if a server on which
your site depends becomes unavailable, it’s critical that a sound redundancy scheme
makes certain that your site remains available. As your organization moves into an e-
business paradigm, you must plan, design, and implement load balancing and failover
strategies that guarantee that your servers will remain operational and serving your
customers.
If servers employ a good strategy for load balancing and failover, there’s no reason why
they should not provide high availability and reliability to their users. In fact, Internet
Service Providers (ISPs) that host commercial Web sites and offer 24x7 technical