MACROMEDIA COLDFUSION 5 - INSTALING AND CONFIGURING SERVER, Manual

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138 Appendix Preparing Your Server for ClusterCATS
Configuring the primary DNS server
You must configure DNS so that the forward and reverse lookup translation entries
are entered and registered correctly with your primary DNS server. To accomplish
this, you must define required DNS records (A records and PTR records) for your
Web servers on your primary DNS server.
Besides standard name translations, your primary DNS server can also distribute
HTTP requests sequentially across clustered servers using a technique called
round-robin DNS . This service allows DNS to return a list of multiple servers back to
the browser that requests a name translation.
Round-robin DNS and ClusterCATS work well together. You do not want to rely on
just round-robin DNS for distributing load for your business-critical sites because
DNS functionality is limited. In short, DNS is a good load distribution technique, but
it cannot manage load because it is unable to react to increases in server traffic. It
also cannot detect server failures nor redirect requests among available servers.
ClusterCATS compensates for these limitations.
The ColdFusion team recommends that you use round-robin DNS or a hardware
load-balancing device to distribute requests initially to the Web servers in your
cluster. Following the initial distribution, the ClusterCATS load management and
failover features automatically take over and ensure that your Web applications
remain up and running.
Using ClusterCATS with round-robin DNS
For high volume sites, you should use round-robin DNS to distribute requests to the
Web servers in your cluster initially. 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. If a server in a
SmartCluster fails, another server on that subnet assumes the IP address of the
failed server.
•
Server Overload Round-robin DNS cannot detect server overloads.
ClusterCATS allows you to configure load thresholds for each server. If the actual
server load exceeds the load threshold, ClusterCATS transparently redirects the
user to another Web server using an HTTP redirect. Once 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 that ClusterCATS operates effectively with round-robin DNS.
For example, for a single-location cluster of servers 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.
The following tables show an example of forward and reverse entries in the DNS.
Host Name IP Address
www.company.com 193.168.0.1
www.company.com 193.168.0.2
install.book Page 138 Thursday, May 10, 2001 12:59 PM