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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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Generic techniques to enhance scalability include clustering, virtualization, <strong>and</strong><br />

the monitoring of devices to ensure that if certain resource thresholds are met,<br />

the resources are upgraded. We discuss clustering <strong>and</strong> virtualization in more<br />

detail later.<br />

24.3 Load balancing<br />

24.4 Clustering<br />

Assigning applications with user connections to a specific system can overload<br />

this system's capacity, while other systems with fewer connection requests to<br />

other applications might waste free capacity.<br />

To reach the goal for an equal level of load of all systems, these systems must<br />

be organized in a clustered system group. All systems in this cluster can provide<br />

information about their workload to the load balancing device. This device will<br />

now be responsible for distributing connection requests from users to the<br />

systems of the application servers, based on workload information.<br />

Users are not aware of such clusters. They try to connect to a service, assuming<br />

it is running in the machine of the load balancer. The load balancer forwards the<br />

connection request to the real service provider based on the current workload of<br />

all systems in the cluster. The information about the state of the workload can be<br />

provided by a function, such as a workload manager residing in every target<br />

system.<br />

If there is no workload information from target systems, the load balancer can<br />

use distribution rules, such as:<br />

► A simple round-robin distribution<br />

► Number of distributed connections<br />

We discuss techniques used to assist with or provide load balancing, scalability,<br />

<strong>and</strong> availability next.<br />

In order to provide the referenced availability requirement, another system<br />

organization has to be applied. This leads to running multiple application<br />

instances on multiple machines, including <strong>TCP</strong>/<strong>IP</strong> stacks with parallel<br />

connections to the <strong>TCP</strong>/<strong>IP</strong> network. This solution, called the clustering technique<br />

in general terms, is used for load balancing purposes but is also valid for solving<br />

high availability requirements.<br />

910 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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