MACROMEDIA COLDFUSION 5-ADVANCED ADMINISTRATION Manual page 261

Techniques for Creating Scalable and Highly Available Sites
Advantages
The following benefits make a software-based clustering solution attractive:
Considerations
Consider the following issues when evaluating software-based solutions for your
environment:
Optimizing load balancing scheme with application-aware and session-aware
load balancing
Automatically detecting failures
Automatically redirecting traffic to available servers
Automatically notifying administrators of problems
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
hardware and software clustering solutions" on page 244
Devices" on page 290
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.
No single point of failure
By distributing the load balancing and failover capabilities among multiple
servers in a cluster or multiple clusters, as opposed to relying on only a single
device, no individual server failure can disable your application.
Differences among feature sets
Not all software-based clustering solutions are the same in terms of capabilities
and features. For instance, some have no automatic failure detection,
notification, or IP address assumption, and others have significantly delayed
detection. Some let you configure load thresholds to enable preventive measures,
some don't. Determine your scalability and failover needs in advance and pick
your solution accordingly.
for more information about how hardware and software
243
"Combining
and "Load-Balancing