MACROMEDIA COLDFUSION 4.5-ADMINISTRING COLDFUSION SERVER Manual page 179

Chapter 6: Creating Scalable and Highly Available Web Sites
Load Threshold Configuration
ClusterCATS lets you configure maximum and gradual redirection thresholds
for each server in a cluster. The maximum threshold indicates the point at
which the server cannot handle any additional load. To prevent a server's load
from reaching this point and resulting in poor performance and unavailability,
you can also configure a gradual redirection threshold that will redirect
requests to a less loaded server when the load reaches the gradual redirection
setting.
Application-Aware Load Balancing
ClusterCATS ensures that your ColdFusion applications always remain up and
running because it understands the load algorithm produced by the
ColdFusion Server (CFS). Consequently, ClusterCATS can redirect HTTP
requests to other Web servers as necessary in response to increases in load
hitting the CFS. Additionally, the new configurable ColdFusion Probe provides
another level of ColdFusion-specific load balancing by detecting whether the
ColdFusion Server is operating properly. If it determines that the ColdFusion
Server has failed or is otherwise unavailable, it redirects traffic to another
available server and attempts to recover the failed ColdFusion Server.
Session-Aware Load Balancing
This feature ensures that your e-commerce applications maintain their state
when users are in the process of shopping, ordering, or paying for their
purchases. Sometimes referred to as a "sticky" session, session-aware load
balancing guarantees that users won't get bumped from the server on which
they started their transaction until the transaction is complete, regardless of the
load thresholds that have been defined for the affected server.
Hardware Load Balancing Device Integration
ClusterCATS for ColdFusion can augment an existing hardware-based load
balancing solution by easily integrating with established devices, such as
Cisco's LocalDirector. Consequently, you are able to take advantage of
ClusterCATS built-in intelligence, resulting in a more comprehensive load
balancing solution.
Failover features
ClusterCATS provides these important failover features:
Continuous IP Monitoring Within Clusters
The ClusterCATS IP monitoring service is a self-monitoring capability that
enables cluster members to listen for server failures within clusters. Each server
that is up and running transmits an IP signal, which indicates that the server is
available and functioning normally. However, if a server fails, it will no longer
transmit a signal, which indicates to the remaining servers that it is no longer
available to respond to HTTP requests.
Automatic IP Address Assumption and HTTP Redirection on Failure
157