Like many great innovations throughout history, the Web caught most by surprise. Its developers let the genie out of the bottle almost accidentally, and its escape has brought untold opportunities to the world of information processing. However, like most genies, the Web also brought great hazards. In exchange for its potential, the Web has triggered a new wave of turmoil and forced evolution in the basic infrastructure that drives the modern enterprise into a new set of assumptions about high availability (HA). The transformation of the Web into an integral part of the enterprise infrastructure has resulted in changes in the characteristics of enterprise IT:
All applications are now 24x7 - With the near-universal worldwide access provided by the Web, almost any Web-based application, especially a public-facing one, is by definition 24x7, even those with low duty cycles. This has challenged the fundamental assumption that there is a maintenance window for business applications, and increased the demand for high-availability solutions, formerly the domain of a select few large applications.
All applications are now mission-critical - When the world can access your application, applications failures are exposed to a much wider community.
All previous assumptions about capacity planning are now obsolete - another consequence of ubiquitous access is unpredictability of loads, challenging established techniques for application capacity planning.
Security risks are magnified - With the entire world at the front door, better locks become mandatory.