MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION..., Manual

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130 Administering ColdFusion Server
What is Scalability?
As an administrator, it’s likely that you often hear about the importance of having Web
servers that scale well, but what exactly is scalability? Simply, scalability is a Web
server’s ability to maintain a site’s availability, reliability, and performance as the
amount of simultaneous Web traffic, or load, hitting the Web server increases.
The major issues that affect Web site scalability include:
•
Performance
•
Load management
Performance
Performance refers to how efficiently a site responds to browser requests according to
defined benchmarks. Application performance can be designed, tuned, and measured.
It can also be affected by many complex factors, including application design and
construction, database connectivity, network capacity and bandwidth, backoffice
services, (such as mail, proxy, and security services), and hardware server resources.
Web application architects and developers must design and code an application with
performance in mind. Once the application is built, various administrators can tune
performance by setting specific flags and options on the database, the operating
system, and often the application itself to achieve peak performance. Following the
construction and tuning efforts, quality assurance testers should test and measure an
application’s performance prior to deployment to establish acceptable quality
benchmarks. If all of these efforts are performed well, consequently you are able to
better diagnose whether the Web site is operating within established operating
parameters when reviewing the statistics generated by Web server monitoring and
logging programs.
Depending on the size and complexity of your Web application, you may be able to
handle anywhere from 10 to 10,000 concurrent users. The number of concurrent
connections to your Web server(s) will ultimately have a direct impact on your sites
performance. Therefore, your performance objectives must include two dimensions:
•
the speed of a single user’s transaction
•
the amount of performance degradation related to the increasing number of
concurrent connections to your Web servers
Thus, you must establish desired response benchmarks for your site and then achieve
the highest number of concurrent users connected to your site at the desired response
rates. By doing so, you will be able to determine a rough number of concurrent users
for each Web server and then scale your Web site by adding additional servers.
Once your site runs on multiple Web servers, you will need to monitor and manage the
traffic and load across the group of servers. See “Hardware planning” on page 148 and
“Techniques for Creating Scalable & Highly Available Sites” on page 149 to learn about
the ways you can do this.