1.5. Overview of the Programming Steps

To make an application highly available, follow these steps:

1. Understand the application and determine:

   • The configuration required for the application, such as user names, permissions, data location (volumes), and so on. For more information about configuration, see the Linux FailSafe Administrator's Guide.

   • The other resources on which the application depends. All interdependent resources must be part of the same resource group.

   • The resource type that best suits this application.

   • The number of instances of the resource type that will constitute the application. (Each instance of a given application, or resource type, is a separate resource.) For example, a web server may depend upon two filesystem resources.

   • The commands and arguments required to start, stop, and monitor this application (that is, the resources in the resource group).

   • The order in which all resources in the resource group must be started and stopped.

2. Determine whether existing action scripts can be reused. If they cannot, write a new set of action scripts, using existing scripts and the templates in /usr/lib/failsafe/resource_types/template as a guide. See Chapter 2.

3. Determine whether the existing ordered or round-robin failover scripts can be reused for the resource group. If they cannot, write a new failover script. See Chapter 4.

4. Determine whether an existing resource type can be reused. If none applies, create a new resource type or modify an existing resource type. See Chapter 4.

5. Configure the following in the cluster configuration database (for more information, see the Linux FailSafe Administrator's Guide):

   • Resource group

   • Resource type

   • Failover policy

6. Test the action scripts and failover script. See Chapter 5, and Section 5.2.

   Note: Do not modify the scripts included with the Linux FailSafe product. New or customized scripts must have different names from the files included with the release.