WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

The Web server plug-in distributes requests to the cluster members on each
server performing load balancing and offers an initial failover just as it does in the
vertical clustering topology. If any component (hardware or software) on System
B fails, the application server on System C can continue to serve requests, and
vice versa.
Note: The illustration in Figure 5-4 is intended to show a horizontal scaling
topology of application servers but still contains single points of failure
(namely, the Web server). To avoid these single points of failures you have to
enhance the topology as shown in “Horizontal scaling topology with an IP
sprayer” on page 150.
Advantages
Horizontal scaling using clusters provides the following advantages:
► Improved throughput
As multiple systems are servicing your client requests simultaneously without
competing for resources, you can expect improved throughput from your
installation.
► Improved response times
Hosting cluster members on multiple machines enables each cluster member
to make use of its machine's processing resources, avoiding bottlenecks and
resource contention. Therefore, response times will improve in most
scenarios.
► Benefits from WebSphere Application Server workload management
capabilities
As horizontal scaling is implemented through clusters, it benefits from
WebSphere Application Server workload management.
► Provides enhanced failover support
As the cluster members are spread over multiple systems, this topology
provides hardware failover capabilities. Client requests can be redirected to
cluster members on other machines if a machine goes offline. The outage of a
system or an operating system failure does not stop your service from
working.
148 WebSphere Application Server V7.0: Concepts, Planning, and Design