MACROMEDIA COLDFUSION 5-ADVANCED ADMINISTRATION Manual page 256

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Systems monitoring
In addition to redundant hardware, you should ensure that your network and the
mission-critical sites that reside on its servers are supported by systems monitoring
software. This type of software actively and continuously monitors an application's
availability and its service levels. These monitoring programs must not only be able
to detect problems, but they must also be able to route alerts to the correct
administrators for immediate notification of problems.
Corrective actions
The third major failover consideration is the corrective actions that need to occur if a
failure causes a server to become unavailable. Generally speaking, if a server goes
down and causes your site to become unavailable, some level of human interaction is
usually required to effectively diagnose and correct the problem.
However, before the analysis and repair can happen, the administrator needs to be
notified. Whatever failover system you put in place, it should include an automated
notification system that can route alerts via your telecommunications infrastructure
(e-mail, pagers, real time web-based alerts, etc.) to the appropriate administrator for
prompt attention.
Besides notifying the administrator that a problem has occurred, you also want your
failover solution to automatically redirect traffic intended for the unavailable server
to other available servers until the unavailable server is fixed. This crucial corrective
action is what keeps your Web site up and available to your users even if one of the
servers supporting it is experiencing problems.
If you plan to use a parallel model, Allaire recommends that you use many middle
range servers rather than fewer high-end ones or lots of inexpensive ones. Servers
that provide adequate capacity and are moderately priced can generally
accommodate all your needs just as well as expensive ones at a fraction of the
cost.
Chapter 11 Scalability and Availability Overview