Configuring HTTP Server Redirection  
 
 

You can configure ClusterCATS redirection to occur for a number of different reasons. However, in each case, what happens is the same: requests initially handled by one server are routed to another server in the cluster. For example, ClusterCATS enables load balancing in a cluster of servers. Load is distributed among a group or cluster of servers. This is achieved by setting limits to the amount of traffic a server can handle. When the level of incoming traffic reaches that predefined level, all subsequent traffic is redirected to the other servers in the cluster.

ClusterCATS supports four types of redirection:

  • Combined with DNS round robin to distribute requests among servers in your cluster
  • Through ClusterCATS transparent redirection of HTTP requests
  • By setting ClusterCATS load threshold, gradual redirect threshold, and Web server state maintenance levels
  • By setting preferred server selections
 
 
  Using ClusterCATS with DNS round robin  
 
 

ClusterCATS works in conjunction with the round robin DNS you may already have in place. More importantly, ClusterCATS eliminates the following two major problems associated with round robin DNS:

  1. Server failure -- Round robin DNS cannot detect server failure. If any server in a ClusterCATS cluster fails, another server on that subnet will immediately and transparently assume the IP address of the failed server.
  2. Server overload -- Round robin DNS cannot detect server overloading. In a ClusterCATS cluster, load thresholds are configured on each server. If actual server load exceeds the load threshold, ClusterCATS transparently redirects the user to another web server. Once redirected, user requests and responses will flow to and from that server directly, minimizing response times throughout the user session.
 
 
  Scheduling and DNS round robin  
 

ClusterCATS clusters support DNS scheduling. With scheduling, you can have client URL requests redirected using DNS round robin to cycle the request through the servers in your round robin cluster. To do this, you create a global name in the DNS hierarchy at the desired level where the round robin name will reside.

For example, if you have three servers named: server1.sales.us.company.com, server2.sales.us.company.com, and server3.sales.us.company.com, you need a DNS object -- for example, www.sales.us.company.com, (or ussales.company.com) -- created at the appropriate level in DNS. Note that your DNS name server must support round robin names.

So that ClusterCATS operates effectively with round robin DNS, you need to make sure it is configured properly. For example, for a single location Web server farm consisting of four servers, you need to configure round robin DNS across all four servers for the domain name and individual IP addresses for each server name. As an example, your DNS tables would look something like the table below.

Example DNS Tables with Round Robin Enabled
Host Name
IP Address
www.mycompany.com
193.168.0.1
193.168.0.2
193.168.0.3
193.168.0.4
www1.mycompany.com
193.168.0.1
www2.mycompany.com
193.168.0.2
www3.mycompany.com
193.168.0.3
www4.mycompany.com
193.168.0.4

round robin DNS distributes the initial domain level requests across all four servers. From there, ClusterCATS distributes load to avoid failed or overloaded servers.



 
 
BackUp LevelNext
 
 

allaire     AllaireDoc@allaire.com
    Copyright © 1998, Allaire Corporation. All rights reserved.