MACROMEDIA COLDFUSION 5-ADVANCED ADMINISTRATION, Manual

Page: 260 / 372

242 Chapter 11 Scalability and Availability Overview
Considerations
Carefully evaluate the following issues against a router’s attributes:
•
Expense
Hardware devices can be expensive relative to some software solutions, even
without yearly licensing fees.
•
Single point of failure
If a problem develops on the load-balancing device itself and it fails, your load
balancing and failover strategies are no longer working. Although some
load-balancing devices come with secondary systems for just this reason, this
additional equipment is often what inflates the overall price of a hardware
solution.
•
Not application-aware
The device cannot be tuned for particular types of Web applications (static vs.
dynamic sites) or for the development tools used to build them (scriptlets vs. JSP
vs. CGI vs. ASP and so on). Consequently, a router cannot measure the
performance of a Web application server.
•
Limited intelligence
The device does not allow you to configure individual load and redirection
thresholds for each server in a cluster, and therefore, it is unable to effectively
manage load to prevent failures.
Software-based clustering solutions
There are several flavors of software-based clustering solutions on the market. Just
like hardware-based clustering solutions, there are strengths and weaknesses
associated with each. These software solutions include:
•
Round-robin DNS
A very popular choice because of its relative simplicity and low implementation
cost, but it does not contain any intelligence for load-balancing or failover.
•
Primary/backup clustering
Two cloned systems provide redundancy for one another. This type of clustering
does not provide any parallel server load balancing.
•
Smart clustering
Combines the advantages of round-robin DNS and backup clustering to provide
simplicity with intelligence and redundancy.
ClusterCATS, Allaire’s software clustering solution for load balancing and high
availability, allows you to easily create, optimize, and maintain “smart” clusters to
support your 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:
•
Configuring load and redirection thresholds per server