Availability Guide for Application Design

What Is Application Availability?

Availability Guide for Application Design—525637-004

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Think Ahead About Changing the Application Online

Upgrading a departmental application from one revision to the next is often a major

reconfiguration effort. This effort can be even larger for an enterprise level application.

By taking the right steps when you first design the application, however, you can

minimize or even eliminate reduced availability or downtime for this task. HP calls this

“future-proofing” your application, and has identified the following requirements:

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Flexibility to accommodate change—Unlike departmental and personal computing

applications, enterprise applications must be designed with a long-term

perspective. Enterprise applications are typically large, complex, distributed

client/server applications, and reengineering them is a time-consuming and

expensive proposition. Therefore, enterprise applications should be designed to

accommodate change. Because business conditions and user requirements are

not predictable (especially over multiple years), enterprise applications must be

adaptable.

A key attribute of adaptability is portability. Each year, new deployment platforms

are introduced to the market, each with its own strengths and weaknesses.

Application developers must be able to take advantage of the most promising and

commercially viable of these opportunities, without sacrificing the uniqueness and

key features of their programs.

•

Continuous availability for continuous commerce environments—Global

organizations must be able to conduct business at all hours of the day or night;

therefore, enterprise applications must be continuously and reliably available. Even

the smallest amount of application downtime can be devastating to a company’s

sales, customer satisfaction levels, and reputation for service.

The continuous availability of enterprise applications is the result of a focus on

failure prevention and rapid recovery. Every facet of the entire system (including

hardware, software, networks, and even the environment and operations practices)

must be designed to maximize uptime. In addition, applications and databases

must be easy to manage on an enterprise scale. Moreover, mechanisms must be

in place to facilitate the recovery from failures that do occur.

•

High scalability to meet fast-changing business needs—The need for absolute

scalability is a key difference between enterprise applications and their more

localized cousins. Enterprise applications must ensure that no limitations exist in at

least two major areas of scalability: internal management of access to shared

resources used by the application, and external manageability of the executing

application itself.

Several design techniques can help, such as designing a requester to be able to talk to

an alternate class of server. Good software engineering practices, such as modular

design and data isolation, will make the upgrade much easier.

Refer to Section 10, Designing Applications for Change, for some guidelines.