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servers, you can't anticipate problems nor determine why they occur. The
number of possibilities would be too large.
Minimize distributed environment load testing
Load testing in a distributed environment can be problematic if the network on
which you are performing your load tests becomes congested, resulting in poor
response times. Additionally, if everyone else in the organization is using that
network for their everyday activities, such as e-mail, source control, and file
management, an increased load going over the network will likely cause
significant network degradation for them. As they likely have nothing to do with
the testing effort, this situation can cause great frustration.
In such a scenario, it may be more effective to physically sit in front of the server
on which the application resides and perform the tests locally rather than bring
the entire LAN or WAN to a slow crawl. Also, by testing locally, you are better
able to rule out the network as the source of the scalability problems.
Alternatively, you may be able to configure a separate subnet on the LAN or
WAN that is distinct from the subnet on which everybody else in your
environment uses network services.
You should now have a good overview of what scalability implies, the core elements
that comprise it, some of the issues that affect successful implementations, and the
tasks that must be performed to verify that your Web applications are able to achieve
satisfactory scalability.
The next section describes Web site availability and reliability concepts and
considerations.
What is Web Site Availability?
As you've already learned from the previous section, it's critical to design, develop, test,
and deploy your Web applications so that they can scale well under heavy and ever-
increasing load. However, the reality is that in spite of the best-laid plans and
preparations, servers can fail for seemingly unknown reasons, causing your site to
become unavailable. If and when a server fails or becomes overloaded, regardless of
why it has, you want to ensure that it won't adversely affect your business by
preventing your customers from accessing and using your Web application. If it does,
you risk jeopardizing your bottom line with lost sales and disgruntled customers who
will look to your competitors' products for goods and services.
This section defines and describes Web site availability and failover. It contains the
following topics:
Availability & reliability
Common failures
A Web site availability scenario
Failover considerations
Administering ColdFusion Server
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