Advanced ColdFusion Administration
Optimizing ClusterCATS

Using Server Failover

The ability to fail over servers that have become unavailable to redundant servers is a cornerstone of any mission-critical application, one that ensures an application's continuous and reliable operation. Server failover was an option to select during the installation process. If you did not select it during installation, you must reinstall ClusterCATS and select that option.

Static versus ClusterCATS dynamic IP addressing

There are two schemes with which you implement server failover:

• Static IP addressing. Under static IP addressing, when a machine fails, the IP address(es) that is bound to its Web server is reassigned to the most available cluster member's Web server. When the failed over server comes back online, it must claim the IP address and then reboot again.
• Dynamic IP addressing. ClusterCATS can be configured to dynamically assign IP addresses so that when a server fails, it's IP address(es) can be assigned to other servers. When the failed over server comes back online, ClusterCATS returns the IP addresses to it without conflict.

On Windows clusters, Allaire recommends that you use server failover with the ClusterCATS dynamic IP address scheme. In order to configure ClusterCATS dynamic IP addresses, the IP address associated with the computer name must be different from the IP addresses associated with the Web sites. ClusterCATS refers to the IP address associated with the computer name as the maintenance address. For more information on setting up your Web site with the ClusterCATS dynamic IP addressing scheme, refer to "ClusterCATS Dynamic IP Addressing (Windows only)".

Windows domain controllers

If you are using Windows NT Domain server authentication, then each web server in a cluster must participate as a member NT Server in a domain. Do not make any server in your cluster the Primary Domain Controller (PDC). Server Fail-Over will interfere with the function of the PDC. One of the NT servers can be a Backup Domain Controller but it is not the recommended configuration.

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