MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Manual page 173

Chapter 6: Creating Scalable and Highly Available Web Sites
selecting the best server to accommodate the traffic. This process is fast and efficient.
The router device in conjunction with the Web servers comprise what is known as a
virtual server.
Routers are considered semi-intelligent devices because they can detect a server
failure and redirect requests to other servers. If a Web server fails or stops responding,
the router stops sending packets to the unresponsive server. Routers are not
considered fully intelligent because while they can redirect requests upon discovering
a failure, they do not allow you to configure redirection thresholds for individual
servers. They also do not provide for application-aware load balancing.
The following figure shows a router distributing requests in round-robin fashion to the
available servers in a Web server cluster.
Advantages
A hardware-based clustering solution, such as a router, is an attractive solution for the
following reasons:
Proven technology
Relatively low complexity
No recurrent licensing fees
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