MACROMEDIA COLDFUSION MX-CLUSTERCATS Use Manual page 47

Using ClusterCATS with round-robin DNS
For high-volume sites, you should use round robin DNS to initially distribute requests to
the web servers in your cluster. The load management component of ClusterCATS
enhances round-robin DNS by eliminating its two major limitations:
Server failure — round-robin DNS cannot detect server failure. Should a server in a
cluster fail, another server on the subnet immediately and transparently assumes the
IP address of the failed server.
Server overload — round-robin DNS cannot detect server overloads. ClusterCATS
lets you configure load thresholds for each server. Should actual server load exceed the
load threshold, ClusterCATS transparently redirects users to another web server,
using an HTTP redirect. When redirected, user requests and responses flow to and
from that server directly, minimizing response time throughout the user session.
You must ensure that round-robin DNS entries are configured correctly on your primary
DNS server so ClusterCATS operates effectively with round-robin DNS. For example,
for a single-location server cluster consisting of four servers, you must configure
round-robin DNS across all four servers for the domain name, and individual IP
addresses for each explicit server name.
For example, the DNS table forward entries on your primary DNS server would be
similar to these:
Host Name
www.company.com
www.company.com
www.company.com
www.company.com
www1.company.com
www2.company.com
www3.company.com
www4.company.com
The DNS table reverse entries on your primary DNS server would be similar to these:
IP Address
193.168.0.1
193.168.0.2
193.168.0.3
193.168.0.4
Note: When using round-robin DNS, do not define a reverse mapping (PTR record) for the
site name (www.company.com); the cluster will not operate properly if you do. Define only
forward mappings (A records) for www.company.com. Define A records and PTR records
for all explicit servers (www1, www2,...) in the cluster. This configuration ensures that
requests cycle through the servers sequentially, or "round-robin."
IP Address
193.168.0.1
193.168.0.2
193.168.0.3
193.168.0.4
193.168.0.1
193.168.0.2
193.168.0.3
193.168.0.4
Host Name
www1.company.com
www2.company.com
www3.company.com
www4.company.com
Before you install 37