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Semi-intelligent
Routers can load balance in a round-robin fashion, and some can detect
failures and automatically redirect traffic and remove failed servers from a
cluster.
Note
Not all routers have the same features or offer the same capabilities.
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 router itself and it fails, your load balancing and
failover strategies are no longer working. Although some routers come with
secondary systems for just this reason, this additional hardware 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 (ColdFusion vs.
ASP vs. CGI vs. Java 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
A software-based solution is another approach to clustering. There are several good
software clustering packages on the market as well as different platform
implementations of the Domain Name System (DNS).
Just like hardware-based clustering solutions, there are strengths and weaknesses
associated with software clustering solutions. For example, while round-robin DNS is a
very popular choice because of its relative simplicity and low implementation cost, it
does not contain any intelligence in balancing load or reacting to server failures. It,
therefore, will not be able to help you prevent server overloads and eventual failures for
highly trafficked sites.
Similarly, Microsoft’s Cluster Server provides failover capabilities for an application’s
messaging related services. It has also proven its reliability with numerous
implementations, and it operates seamlessly with Microsoft’s NT operating system and
IIS Web server. The type of clustering that Cluster Server provides is known as Primary/
Summary of Contents for COLDFUSION 4.5-ADMINISTRING COLDFUSION...
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