MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Manual page 175

Chapter 6: Creating Scalable and Highly Available Web Sites
Backup clustering, in which two cloned systems provide redundancy for one another.
This type of clustering does not provide any parallel server load balancing.
Additionally, Cluster Server has some limitations. Its shortcomings include lengthy
durations in detecting server failures (up to 10 minutes) and not being able to provide
Exchange-specific failure detection.
ClusterCATS, Allaire's embedded software clustering solution for load balancing and
high availability, allows you to easily create, optimize, and maintain "smart" clusters to
support your ColdFusion Web applications. ClusterCATS runs on NT, Solaris, and
Linux platforms and works with leading mission-critical Web servers, including
Microsoft IIS, Netscape Enterprise Server, and Apache. It is easily administered from
remote locations and provides robust features, including the ability to:
configure load and redirection thresholds per server
optimize your load balancing scheme with application-aware and session-
aware load balancing
automatically detect failures
automatically redirect traffic to available servers
automatically notify administrators of problems
Advantages
The following benefits make a software-based clustering solution attractive:
Relatively low expense
Compared to the cost of hardware devices, such as routers or switches,
software-based clustering solutions are relatively inexpensive. In fact, you can
cheaply implement Internet DNS on UNIX and Windows platforms for initial
load balancing needs and augment it with third-party clustering software.
Flexibility
Some clustering software can augment existing hardware devices, thereby
providing a more robust load balancing and failover solution. Additionally, by
integrating hardware with software, you diminish, if not eliminate, losses on
capital expenditures that your organization has already made. See "Combining
hardware and software clustering solutions" on page 154 and "Integrating
ClusterCATS with load balancing devices" on page 211 for more information
about how hardware and software solutions can be integrated.
Intelligence
Some software solutions provide a level of intelligence that enables preventive
load balancing measures that actually minimize the chance of servers
becoming unavailable. In the event that a server does becomes overloaded or
actually fails, some software can automatically detect the problem and reroute
HTTP requests to available servers in the cluster.
2. Microsoft Corporation. "Microsoft Exchange 5.5: Windows NT Clusters White Paper." Redmond, WA:
Microsoft Corporation, 1997.
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