Common Failures; A Web Site Availability Scenario - MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Manual

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support as a competitive service differentiator will typically specify in written service-
level agreements (SLA) a percentage of time that they guarantee a Web site will be
available. If the ISP has a sound scalability and failover strategy in place, this figure is
usually in the range of 99% or better.

Common failures

Following are typical types of failures that can negatively impact your Web
application's availability and reliability:
Hardware failures — While less common than software failures, hardware
failures do occur and may include crashed hard drives, blown processors, and
corrupted network cards. Diagnosing and fixing these kinds of issues can be a
lengthy endeavor because of time spent procuring the parts and performing
the labor. If your Web application is mission-critical, you should ensure a sound
hardware redundancy strategy to avoid costly downtime. A sound strategy
includes a minimum of two Web servers but preferably three.
Software failures — The types of software failures that will most likely affect a
Web application involve the Web server's operating system, the Web server
software itself, or the Web application software. If the operating system crashes
or becomes corrupt, the Web server cannot function properly (or perhaps at
all), causing your Web application's availability, reliability, and performance to
be compromised. Similarly, if the Web server software crashes or acts erratically,
it will likely cause the Web server to stop running when you didn't intend it to.
It's hard to prepare for software failures, but if you have mirrored secondary
hardware systems in place to account for failures, you'll minimize your Web
application's downtime.
Server failures — In addition to the Web server, other servers on which your
Web application depends can also fail, causing either downtime or diminished
capabilities on your site. For example, for distributed applications, a proxy
server may go down, causing requests for your Web application's services to go
unanswered. Or, the database server can crash, making it impossible for users
to submit or retrieve information from your database. Or, a mail server can go
down, making it impossible for your users to successfully send mail to you.
Ensure that your organization's IT architecture includes network monitoring
and notification software that can quickly report on the general health of your
network and alert you about any failed servers.

A Web site availability scenario

Imagine that you've just built a robust, interactive e-commerce Web site on which you
plan to sell the most sought-after books and music in the world. You've used
ColdFusion to build the application, so of course you've taken advantage of it's many
built-in features, including:
back-end relational database support to manage inventory control and order
submissions
Administering ColdFusion Server