Plan Concepts

A plan, also called an execution plan, is a sequence of instructions that is used to manage one or more components on the specified hosts. For example, an execution plan might install three components and initiate the “startup” control of another component.

A plan can also include a sequence of other plans, which enables common instruction sequences to be written as plans and then shared among plans. For example, a plan might instruct the provisioning system to install three components and initiate the startup control for another.

The provisioning system provides an in-memory representation of the objects expressed by the XML schema. This representation also defines a process for the validation, persistence, and version control for those objects.

When the provisioning system executes a plan, substitution variables that are declared by a component are replaced by actual values. The provisioning system also supports a notification feature that can send email in response to events that are related to plan execution.

Plan Types

The provisioning system supports two types of plans:

• Simple plans. A simple plan contains a collection of simple steps, but cannot call other plans.

• Composite plans. A composite plan contains only other plans, called subplans.

The XML schema enforces the distinction between the two types of plans. Thus, you can use a top-level plan that contains calls to other subplans, or a simple plan that contains simple steps but no calls to subplans.

This distinction is important because the steps in a simple plan can only execute on the same set of target hosts, whereas the steps of a composite plan can execute on different sets of target hosts. A composite plan can use one set of target hosts for each simple plan that it contains.

Step Overview

Steps are simple instructions that can be part of both plans and components. The provisioning system supports the following kinds of steps:

• Steps that can only be called from within a component. Such steps can only be called from install blocks or from uninstall blocks. See Install-Only Steps for Components in N1 Grid Service Provisioning System 5.0 XML Schema Reference Guide and Uninstall-Only Steps for Components in N1 Grid Service Provisioning System 5.0 XML Schema Reference Guide.

• Steps that can only be called from a plan. Such steps can only be called from composite plans or from simple plans. See Plan-Only Steps for Composite Plans in N1 Grid Service Provisioning System 5.0 XML Schema Reference Guide and Plan-Only Steps for Simple Plans in N1 Grid Service Provisioning System 5.0 XML Schema Reference Guide.

• Steps that can be called from either a plan or from a component. See Chapter 2, Shared Schema Used by Components and Simple Plans, in N1 Grid Service Provisioning System 5.0 XML Schema Reference Guide.

Component References

A number of steps can reference components in the following situations:

• Components that have yet to be installed can use the <install> step.

  Steps that refer to components that have yet to be installed only need to specify the name of the component and an optional version.

• Components that have already been installed can use the following steps:

  • <uninstall>

  • <call>

  • <checkDependency>

  • <createDependency>

  • <addSnapshot>

  Steps that refer to an installed component must specify the installPath attribute because the same component can be installed more than once on the same server.

Example 1–1 Using Component References

Assume that the “Apache” component is installed on a host with the following attribute settings.

The following shows which installed component is referenced when values for various combinations of the installPath and version attributes are supplied.