Easy High Availability


Today, increasingly more companies realize the importance of high availability for their Web serving business, so that they can provide reliable services to their customers. Highly available HTTP servers take advantage of IBM i clustering technology and make it possible to build a highly available Web site.

Three Web-server cluster models are currently supported for highly available HTTP servers:

»Primary or backup with takeover Internet Protocol (IP) model
»Primary or backup with a network dispatcher model
»Peer model

This article will describe how to make your Web environment high available with the primary or backup with takeover IP model by using PowerHA on IBM i. From the technical perspective, the takeover IP model is the fastest and easiest way to help you make your Web serving highly available, and it doesn't require any extra technology or software to implement. The other two models require additional software, such as the IBM WebSphere Edge Server, to set up your highly available Web environment.

Defining the Model

In a primary or backup with takeover IP model, the Web server runs on the primary and all backup nodes. The backup node or nodes are in an idle state, ready to become the primary Web server should the primary Web server fail (failover) or a switchover takes place. Client requests are always served by the primary node. Currently, this model can only support IPv4 and is not supported prior to V5R1 systems. Figure 1 illustrates a primary or backup with takeover IP model.

Let's look at the detailed steps of how to configure high availability for Web server on IBM i. 

Preparation: Software Requirements

5770HAS PowerHA SystemMirror for i
5770DG1 *BASE IBM HTTP Server for i

5761HAS PowerHA for i
5761DG1 *BASE IBM HTTP Server for i

Step 1. Set Up and Precheck the System

To set up your system, use the following parameters:

System Name I/P Address Use
Machine1 Primary System - Node A
Machine2 Backup System - Node B
Machine1 & Machine2 IP takeover address


Xu Le is a member of the IBM CSTL Web integration team in China.

Zhao Ming Ming is a member of the IBM CSTL Web integration team in China.

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