Issues Affecting Successful Scalability Implementations; Designing And Coding Scalable Applications - MACROMEDIA COLDFUSION 5-ADVANCED ADMINISTRATION Manual

Issues Affecting Successful Scalability Implementations

Issues Affecting Successful Scalability
Implementations
Achieving scalable Web servers is not a trivial task. There are various solutions to pick
from, setup and configuration tasks to understand and perform, and many delicate
dependencies between related but heterogeneous technologies. This section
describes some of the major issues affecting successful scalability implementations.
This section discusses the following topics:

Designing and coding scalable applications

Application architects must create designs that are inherently flexible by relying
upon open standards that don't restrict the application's construction and
implementation to vendor-specific interfaces and tools. Similarly, the Web
developers that construct the designed application must be aware that they can
significantly impact the application's scalability in the way in which they write their
code, build their SQL queries, invoke thread management, access databases, and
partition the application.
This section discusses the following topics to consider when designing and building
a Web application:
Application session and state management
As you create Web applications, you will likely create specific variables that you
intend to carry across multiple interactions between a user's browser and a site's Web
server(s). Using client variables that get stored in a shared state repository or session
variables that get stored in memory of a specific server are popular approaches for
accomplishing this. The latter approach, however, introduces a significant challenge
for a Web site that is supported by multiple servers. Once a user has begun a session
and variables are stored on a specific server, the user must return to that server for
the life of the session to maintain correct state information.
A good example that illustrates this concept is an e-commerce application that uses
shopping carts. With this type of application, as a customer accumulates items in his
or her cart, there must be a mechanism that ensures that the user can see the items
as they are added. One approach is to store these items in session variables on a
specific Web server. However, if you use this approach, there must also be a way to
ensure that the user always returns to the same server for the life of the session.
ClusterCATS for ColdFusion automatically handles this for you.
"Designing and coding scalable applications" on page 225
"Avoiding common bottlenecks" on page 227
"DNS effects on Web site performance and availability" on page 228
"Load testing your Web applications" on page 231
"Application session and state management" on page 225
"Database locking and concurrency issues" on page 226
225