User Guide

228 Chapter 11 Scalability and Availability Overview
• Databases Database access, while vitally important to your application’s
capabilities and feature set, can be costly in terms of performance and scalability
if it is not engineered efficiently. When creating data sources for accessing your
database, use a native database driver rather than an ODBC driver if possible
because it will provide faster access. Similarly, try to reduce the number of
individual SQL queries that must be repetitiously constructed and submitted by
placing common database queries in stored procedures that reside on the
database server. In short, tune your databases and queries for maximum
efficiency.
DNS effects on Web site performance and availability
Improper Domain Name System (DNS) setup and configuration on Web servers is
one of the most common problems administrators encounter. This section addresses
the following topics:
• “What is DNS?” on page 228
• “DNS effects on site performance and availability” on page 228
• “DNS core elements” on page 229
What is DNS?
DNS is a set of protocols and services on a TCP/IP network that allows network users
to use hierarchical natural language names rather than computer IP addresses when
searching for other computer hosts (servers) on the network. DNS is used extensively
on the Internet as well as on private enterprise networks, including LANs and WANs.
The primary capability contained within DNS is its ability to map host names to IP
addresses, and vice-versa. For example, suppose the Web server at Allaire has an IP
address of 157.55.100.1. Most people would connect to this server by entering the
domain name (
www.allaire.com) and not the less friendly IP address. Besides being
easier to remember, the name is more reliable because the numeric address could
change for a variety of reasons, but the name can always be reserved.
DNS effects on site performance and availability
Internet DNS is a powerful and successful mechanism that has enabled huge
numbers of individuals and organizations to create easily locatable Web sites on the
Internet. However, DNS by itself may not allow your Web site to perform and scale as
it needs to, thus causing it to become unavailable and unreliable. Whether or not you
use DNS by itself to load balance inbound traffic depends largely on the site’s
purpose and the amount of concurrent activity you expect on it. For instance, a low
volume, static site that only provides textual HTML information can likely be
accommodated just fine by round-robin DNS. However, a high volume, dynamic,
e-commerce site that you anticipate doing lots of volume likely won’t perform or
scale well ultimately if it is only supported by round-robin DNS.
To understand why, let’s look further at the e-commerce example. Even if you have
planned ahead and set up multiple servers to support this high volume site, if you
rely only on DNS, it can only do two things: