Teste

Capacity planning addresses the unpredictable workload of an e-business to produce a competitive and cost-effective architecture and system.
Virgílio A.F. Almeida and
Daniel A. Menascé

Capacity Planning:
An Essential Tool for
Managing Web Services

S

peed, around-the-clock availability, and security are the most common indicators of quality of service on the Internet.
Management faces a twofold challenge.
On the one hand, it must meet customer expectations in terms of quality of service. On the other hand, companies have to control IT costs to stay competitive.Therefore, capacity, reliability, availability, scalability, and security are key issues to
Web services managers. E-business sites are complex system architectures with multiple interconnected layers composed of many software and hardware components, such as networks, caching proxies, routers, load balancers, high-speed links, and large-database mainframes. The e-business workload—composed of transactions and requests submitted to e-business services—is also complex because of its bursty and highly skewed load characteristics. Security and authentication requirements, payment protocols, and the unpredictable characteristics of Internet service requests add to the complexity.
For example, it is common for Web sites to experience, without warning, a manifold increase in traffic volume. This type of load spike, also known as a flash crowd, creates terrible performance problems and slow download times. Such Web delays frustrate customers and cost online business over
$4 billion each year, according to a report from IntelliQuest, a market
Resources
research firm (http://www.intelliquest. com). Inside

1520-9202/02/$17.00 © 2002 IEEE

That’s why planning e-business service capacity requires more than just adding extra hardware based on intuition, ad hoc procedures, or rules of thumb. Many possible alternative architectures can implement a Web service; you must