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Manual Chapter: Introducing the Policy Tree
Manual Chapter
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Acceleration policies are organized in the Policy Tree, which you access from the Policy Editor screen. The Policy Tree is made up of three types of nodes:
Root node
Root nodes exist only for the purpose of inheritance. The WebAccelerator system does not perform matching against root nodes. The Policy Tree typically has only one root node, from which all other nodes are created. You create rules at the root node level to easily propagate the same rule parameters to one or more branch nodes. Root nodes can have multiple branch nodes. What distinguishes a root node from a branch node is that a root node has no parent node.
Branch node
Branch nodes exist only for the purpose of inheritance. The WebAccelerator system does not perform matching against branch nodes. You create rules at the branch node level to easily propagate the same rule parameters to one or more leaf nodes. Branch nodes can have multiple leaf (child) nodes, as well as child branch nodes.
Leaf node
The WebAccelerator system performs application matching for responses and requests only to leaf (child) nodes. A leaf node inherits rule parameters from its parent branch node.
To view specific matching and acceleration rules, you click a leaf node on the Policy Tree. Once you select a leaf node, you can click the matching and acceleration rules on the menu bar to view specific rule parameters for each node.
Each leaf node in the Policy Tree contains specific matching rules to which the WebAccelerator system matches incoming requests, (as described in Reviewing matching rules). In the event that a request matches two leaf nodes equally, the WebAccelerator system matches to the leaf node with the highest priority in the Policy Tree. Once the WebAccelerator system has matched an incoming request to a nodes matching rule, it applies that nodes corresponding acceleration rules.
1.
On the Main tab of the navigation pane, expand WebAccelerator and click Applications.
The Applications screen opens in a new window.
2.
On the Main tab of the navigation pane in the new window, click Policies.
The Policies screen opens, displaying a table of user-defined and pre-defined acceleration policies.
3.
Click the name of the acceleration policy that you want to view.
The Policy Editor screen opens, with the Policy Tree to the left of the screen. The nodes are displayed in the Policy Tree in order of priority.
Since a leaf node in a Policy Tree inherits the rules from its root node and branch node, you can quickly create multiple leaf nodes that contain the same rule parameters. If you override or create new rules at the branch node level, the WebAccelerator system propagates those changes to the associated leaf nodes. After you create the root node and branch node, and then propagate the rule parameters to one or more leaf nodes, you can change rule parameters at the leaf node level, by overriding the inherited rules.
Figure 4.1 shows an example of a Policy Tree. For this Policy Tree, the acceleration policys rules are defined at the Home root node and the Application branch node and the Default and Search leaf nodes inherit these rules. This is illustrated by the fact that the Default and Search leaf nodes and the Application branch node are a subset of the Home root node.
This example Policy Tree also contains a second root node named Images that contains the branch nodes Documents, Components, and Other with associated child nodes. The Images root node contains different rule parameters than the Home root node.
If you create a user-defined acceleration policy by copying an existing acceleration policy, you must determine from which Policy Tree node the acceleration policy is inheriting specific rules, and decide whether you want to change the rules at the leaf node or change the rules at the parent branch node. To determine inheritance for a rule parameter, view the rule parameters inheritance icon.
For example, Figure 4.2 illustrates configured Path and Header rule parameters for a particular leaf node.
The arrow icon in the Inheritance column next to Path indicates that the Path parameter is inherited from the branch node. The inheritance icon next to the Header parameter does not have an arrow, indicating that it is not inherited, and was created locally, at the leaf node.
Since the Header parameter is not inherited, you can delete it at the leaf node level. However, you cannot delete the Path parameter because it was inherited from the branch node. To delete the Path parameter, you must delete it at the ancestor branch node level.
For inherited rule parameters, you can determine the ancestor branch node at which the rule was originally set by placing the cursor over the inheritance icon. For this example, to view the branch node from which the Path parameter was inherited, place your cursor on the inheritance icon next to Path. The defining branch node name displays next to the rule parameter, as illustrated in Figure 4.3.
When editing an inherited rule at the leaf node level, you can change a parameter value and any associated options. The changes you make override the inherited settings for the specified parameter at the leaf node.
When you override rules at the leaf node, the rule at that level is displayed with an override icon. For example, for the content assembly rule in Figure 4.4, all of the options are inherited from the branch node, except for the Enable Content Compression feature, which is overridden at the leaf node. This override is indicated by the inheritance icon with a red X next to Enable Content Compression.
That means that when you created this leaf node, you used all of the content assembly rule parameters from the parent branch node, except for Enable Content Compression. The override icon displays only for the parameters at the current leaf node. To see the point at which the parameter was overridden, place the cursor over the override icon.
To see if the current leaf node inherited an overridden option, click the parent node and view its rules. For example, the parent leaf node may appear as shown in Figure 4.5.
In this instance, no rules are overridden, which means the rules were inherited at the grandparent leaf node. To confirm this, view the grandparents leaf node, which appears as in Figure 4.6.
By following the inheritance, we see that all the rule options are actually set at the grandparents leaf node. The rule parameters are not inherited from any other node, and they are all enabled. Therefore, if you want to enable the content compression feature at the original leaf node, you can use one of the following options:
Cancel the override setting at the parent, so that the parent inherits the Enable Content Compression setting of the grandparent, and in turn, passes that setting to the leaf node.
It is important to keep in mind that if you cancel the override setting at the grandparent leaf node, you change the settings for all the child leaf nodes, not just the leaf node you want to change. Although you have the option to override rules at the leaf node level, you should set up the Policy Tree in a logical way so that you only specify rules for branch nodes that you want most of its child leaf nodes to inherit. In other words, do not set a rule for a branch node if you know that most its leaf nodes will not use that rule.
You create a user-defined acceleration policy by copying an existing acceleration policy, and editing it on the Policy Editor screen. You can customize the copy of the acceleration policy that you created by modifying the branch and leaf nodes in the Policy Tree, as required.
Add
Use this option to add a new branch or leaf node.
Rename
Use this option to edit a branch of leaf nodes name and description.
Delete
Use this option to delete a branch or leaf node.
Copy
Use this option to copy a branch or leaf node.
 
Up button, Down button
Use these options to move the priority of a leaf node up or down within the branch.
Note: You can change the priority of a leaf node only within a branch of the tree. For example, in Figure 4.1, you can give the Default leaf node priority over the Search leaf node, but not over the Images node.
1.
On the Policy Tree function bar, click Add.
The screen refreshes to display the Add Node to Policy Tree form.
2.
In the Name box, type a name for the new branch.
3.
In the Description box, type an optional description.
4.
Check the Create a new Policy Tree branch box.
5.
Click the Create button.
The screen refreshes and the Policy Tree displays with the new branch. You must then create the matching and acceleration rules for the new branch.
2.
On the Policy Tree function bar, click Add.
The screen refreshes to display the Add Node to Policy Tree form.
3.
In the Name box, type a name for the new leaf node.
4.
In the Description box, type an optional description.
5.
Click the Create button.
The screen refreshes and the Policy Tree displays with the new node. The new leaf node inherits all of the matching and acceleration rules from its parent branch node.
2.
On the Policy Tree function bar, click Rename.
The screen refreshes to display the Rename Node form.
3.
In the Name box, type a new name for the node as required.
4.
Click the Rename Node button.
The screen refreshes and the Policy Tree displays the node with the new name.
2.
On the Policy Tree function bar, click Delete.
The screen refreshes to display a confirmation.
3.
Click the Delete button.
The screen refreshes and the Policy Tree displays, without the node you removed.
2.
On the Policy Tree function bar, click Copy.
The screen refreshes to display the Copy Node form.
3.
In the Name box, type a name for the new node.
4.
In the Description box, type an optional description.
5.
Click the Create button.
The screen refreshes and the Policy Tree displays with the node you copied.
2.
On the Policy Tree function bar, click the Up or Down button.
The node changes positions in the Policy Tree, as directed.
This section of the chapter provides information about how to configure an example Policy Tree for a user-defined acceleration policy. For this example, your site receives four basic types of requests. The request types and the associated URLs are as follows.
 
Requests for the home page. For example:
http://www.siterequest.com/
http://www.siterequest.com/index.jsp
 
Requests for non-graphic content. For example:
http://www.siterequest.com/apps/doSomething.jsp
http://www.siterequest.com/apps/doSomethingElse.jsp
http://www.siterequest.com/apps/doAnotherThing.jsp
 
Requests for search applications. For example:
http://www.siterequest.com/srch/doSearch.jsp
http://www.siterequest.com/srch/doSimpleSearch.jsp
 
Requests for graphics images. For example:
http://www.siterequest.com/images/<someimage>.gif
For the site in this example, you create a Policy Tree with the following three top-level nodes. (The names of the nodes are arbitrary.)
Home
Specifies the rules related to the home page.
Applications
Specifies the rules related to the applications for the site with the following leaf nodes:
Default
Specifies the rules related to non-search related applications.
Search
Specifies the rules related to your sites search application.
Images
Specifies the rules related to graphics images.
1.
On the Main tab of the navigation pane, expand WebAccelerator and click Applications.
The Applications screen opens in a new window.
2.
On the Main tab of the navigation pane in the new window, click Policies.
The Policies screen opens, displaying a table of user-defined and pre-defined acceleration policies.
3.
Click the Create button above the User-defined Acceleration Policies table.
The New Policy screen opens.
4.
In the Name box, type a name for the new acceleration policy.
5.
In the Description box, type an optional description.
6.
Click the Create button.
The Policies screen refreshes with the new acceleration policy that you created in the User-defined Acceleration Policies table.
1.
On the Policy Tree function bar, click Add.
The screen refreshes to display the Add Node to Policy Tree form.
2.
In the Name box, type a name for the new node.
For this example, type Home.
3.
In the Description box, type an optional description.
4.
Check the box next to Create a new Policy Tree branch.
5.
Click the Create button.
The Policy Tree refreshes, displaying the new Home branch node.
6.
Repeat steps 1 through 5 to create the Application and Images nodes.
1.
2.
On the Policy Tree function bar, click Add.
The screen refreshes to display the Add Node to Policy Tree form.
3.
In the Name box, type a name for the new node.
For this example, Default.
4.
In the Description box, type an optional description.
5.
Click the Create button.
The Policy Tree refreshes, displaying the new leaf node.
6.
Repeat steps 1 through 5 to create the Search leaf node.
The Policy Tree refreshes, displaying the new leaf node.
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