# Introducing ClusterCATS for ColdFusion

ClusterCATS for ColdFusion is a Web server clustering technology that provides load balancing and failover services that assure high availability for your Web server and ColdFusion Server (CFS). ClusterCATS lets you cluster distributed servers into a single, high-performance, highly available environment of Web server resources.

A cluster consists of two or more Web servers located on a LAN or across a WAN. Web servers included in a cluster operate as a single entity to provide rapid and reliable access to resources on those Web servers. A cluster can help your Web site avoid the consequences of busy and failed servers -- slow networks. With ClusterCATS you can avoid bandwidth, latency, and congestion problems.

This section addresses the following topics:

- ClusterCATS for ColdFusion Features
- ClusterCATS for ColdFusion Components

## ClusterCATS for ColdFusion Features

The ClusterCATS technology embedded in ColdFusion Enterprise provides robust features for load balancing and failing over servers.

This section describes the following ClusterCATS' features:

- "New clustering features available with ColdFusion v4.5"
- "Important ease-of-use features"
- "Load balancing features"
- "Failover features"

### New clustering features available with ColdFusion v4.5

ColdFusion Enterprise v4.5 includes these new ClusterCATS features:

- Additional Platform Support

  ClusterCATS now supports server clusters on the Linux operating system as well as Windows NT and Sun Solaris.

- Additional Web Server Support

  ClusterCATS now supports the Apache Web Server for hosting UNIX-based server clusters in addition Netscape Enterprise Server.

- Automated System Configuration Check (NT/IIS Only)

  Performs various system checks to ensure that your Windows NT/IIS Web servers are configured properly for use with ClusterCATS. This capability checks for the existence of multiple NICs, whether the Streams Environment is installed and configured correctly, and whether the All Unassigned setting for IP address assumption on failover is configured.

- ColdFusion Probe

  Provides another level of ColdFusion-specific load balancing by actively monitoring the ColdFusion Server for failures via application probes that you create to periodically test a ColdFusion URL on your site. If the Probe's validation test fails, it restricts the Web server on which the site resides and redirects the restricted server's HTTP traffic to another server in the cluster. This new feature extends ClusterCATS' automatic monitoring and failover capability.

- Tighter Integration with Cisco LocalDirector

  ClusterCATS is now able to provide the availability and load balancing data it acquires directly to a Cisco LocalDirector so that the LocalDirector can route inbound HTTP traffic to the most appropriate Web server in your cluster.

### Important ease-of-use features

These ClusterCATS features make creating and managing your server clusters easy, fast, and secure:

- Graphical Administration Utilities

  The Windows-based Explorer allows you to centrally administer NT or UNIX clusters easily and quickly. If you run a UNIX-only environment and do not have a Windows machine (NT, 98, or 95) on which to install the Windows-based Explorer, you can use the Web-based ClusterCATS Explorer together with included server utilities to administer your cluster members.

  Note | The Web-based Explorer does not contain all of the configuration and administration features found in the Windows-based Explorer. See "Using the ClusterCATS Web Explorer" for details.

  The ClusterCATS Server Administrator lets you perform maintenance and troubleshooting tasks on each server in your cluster. These tasks include putting a server into maintenance mode so that you can update software or content, stopping and starting the ClusterCATS service, and adding and removing the ClusterCATS filter from the Web server service.

- Cluster Administration Security

  ClusterCATS provides three administrator security levels that you can configure for the appropriate level of security within your organization.

- Offline Maintenance Support (Windows NT only)

  ClusterCATS lets you configure an additional IP address for each Windows server in your cluster so that you can perform update and server maintenance tasks without removing the server from the cluster or disconnecting it from the network

### Load balancing features

ClusterCATS provides the following load balancing features:

- 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

  If a server within a cluster fails or becomes unavailable and is no longer transmitting an IP signal, another available server in the cluster will automatically assume the IP address of the failed server. Subsequent HTTP requests that are bound for the downed server will be redirected to the server that has taken over for its failed counterpart. When the failed server is fixed and comes back online, the server that has assumed the failed server's IP address relinquishes it to the fixed server. This process is known as IP aliasing.

- Automatic Administrator Notification

  ClusterCATS lets you configure automatic e-mail-based alarms for a wide range of failure types. This feature ensures that you can attend to failed servers quickly and minimize server downtime. During regular business hours, you can scan and read your e-mail as usual. For off-hour periods, you can configure your pager to receive e-mail notifications for 24x7 notification capability.