MACROMEDIA COLDFUSION MX-CLUSTERCATS, Руководство пользователя

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Creating scalable and highly available sites 31
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 with third-party clustering software.
•
Flexibility — some clustering software can augment existing hardware devices,
providing a more robust load-balancing and failover solution. By integrating
hardware with software, you diminish, if not eliminate, losses on capital expenditures
that your organization has already made. For more information, see
“Combining
hardware and software clustering solutions” on page 32 and “Load-balancing devices”
on page 92 .
•
Intelligence — some software solutions provide a level of intelligence that enables
preventive load-balancing measures that actually minimize the chance of servers
becoming unavailable. If 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.
Considerations
Consider the following issues when evaluating software-based solutions for your
environment:
•
Differences among feature sets — software-based clustering solutions differ in their of
capabilities and features. For instance, some lack automatic failure detection,
notification, or IP address assumption, and others have significantly delayed
detection. Some let you configure load thresholds to enable preventive measures, and
some don’t. Determine your scalability and failover needs in advance and pick your
solution accordingly.
•
Platform constraints — determine whether the software solution is available on your
platform and operates with your preferred web server. When reviewing data sheets
and other marketing collateral from vendors, ensure that the robust features you want
are available on the platform you need.
•
Level of complexity — some software-based clustering solutions relatively simple.
Others introduce more complexity because of the features offered, the amount of
initial configuration and subsequent administration, or the amount of integration
that must occur between other systems and devices.