MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION..., Руководство пользователя

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150 Administering ColdFusion Server
Clustering for scalability works by distributing load among each server in the cluster
(load balancing) using either an unintelligent-but-regular distribution sequence
(round-robin DNS and routers) or a predefined threshold or algorithm that you specify
and can adjust for each server in the cluster (specialized clustering software).
Clustering for failover relies on redundant servers to ensure that business-critical
applications remain available if one of the servers in a cluster fails. Intelligent
software-based failover solutions can detect when a server has failed and
automatically redirect new incoming HTTP requests to the cluster members that are
available. Some hardware-based failover devices that have less built-in intelligence
require an administrator’s intervention once the failure is detected.
Clustering can be accomplished using software-based solutions, such as round-robin
DNS by itself or together with a third-party package, a hardware-based solution, such
as a packet router, or a combination of the two.
Hardware-based clustering solutions
The most common and reliable hardware-based clustering solution is a device known
as a packet router. One of the most popular routers on the market is Cisco System’s
LocalDirector. A router sits in front of a cluster of Web servers and directs incoming
HTTP requests to available Web servers that form the cluster. A router works by
assessing the speed and volume of IP packet flow to and from the Web servers and then