Creating scalable and highly available sites
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Hardware-based clustering solutions
A common and reliable hardware-based clustering solution is a packet router. One of the
most popular routers is Cisco Systems’ LocalDirector. A router, in front of a cluster of
web servers, directs incoming HTTP requests to available web servers in the cluster. A
router works by assessing the rate and volume of IP packet flow to and from web servers,
and selecting the best server to accommodate the traffic. This process is fast and efficient.
The router and clustered web servers comprise 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 let you configure redirection thresholds for individual servers. They also do not
support 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 of hardware-based solutions
A hardware-based clustering solution, such as a router, is an attractive solution for the
following reasons:
•
It uses proven technology
•
It is has relatively low complexity
Summary of Contents for ClusterCATS
Page 1: ...macromedia Using ClusterCATS ...
Page 56: ...46 Chapter 3 Installing ClusterCATS ...
Page 118: ...108 Chapter 4 Configuring Clusters ...
Page 156: ...146 Index ...