Distributed Systems - Guide to Cloud Computing for Business and Technology Managers - page 67

3
Distributed Systems
3.1 Distributed Applications
Distributed applications consist of a collection of heterogeneous but fully
autonomous components that can execute on different computers. While
each of these components has full control over its constituent subparts, there
is no master component that possesses control over all the components of a
distributed system. Thus, for the system to appear as a single and integrated
whole, the various components need to be able to interact with each other via
predefined interfaces through a computer network.
The characteristic global features of a successful distributed application
are as follows:
• Distributed systems are heterogeneous, arising from the need to, say,
integrate components on a legacy IBM mainframe with the compo-
nents newly created to operate on a UNIX workstation or Windows
NT machine.
• Distributed systems are scalable in that when a component becomes
overloaded with too many requests or users, another replica of the
same component can be instantiated and added to the distributed
system to share the load among them. Moreover, these instantiated
components can be located closer to the local users and other inter-
acting components to improve the performance of the overall dis-
tributed system.
• Distributed systems execute components concurrently in a multi-
threaded mode via multiply invoked components corresponding to
the number of simultaneously invoked processes.
• Distributed systems are fault tolerant in that they duplicate compo-
nents on different computers so that if one computer fails, another
can take over without affecting the availability of the overall system.
• Distributed systems are more resilient in that whereas distributed
systems have multiple points of failure, the unaffected components
are fully operational even though some of the components are not
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