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Manual Chapter: Understanding the Policy Tree
Manual Chapter
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Matching rules and acceleration rules for acceleration policies are associated with nodes that are organized on the Policy Tree, which you access from the Policy Editor screen. The Policy Tree consists of root nodes, leaf nodes, and branch nodes. Typically there is only one root note assigned to the Policy Tree. What distinguishes a root node from a branch node, is that a root node has no parent node, and the WebAccelerator system does not perform application matching on a root note. This structure supports a parent-child relationship, so that you can make changes to rule parameters at the root or branch (parent) node and propagate them to the associated leaf (child) nodes.
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, pre-defined, and signed 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 on the Policy Tree in order of priority.
Figure 4.1 shows an example of a Policy Tree.
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. For the example illustrated in Figure 4.1, the root node is Home. 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. For the example illustrated in Figure 4.1, the branch nodes are Applications, Images, Documents, Components, and Other. 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. For the example illustrated in Figure 4.1, the leaf nodes that are displaying are Default and Search.
To view specific matching rules and acceleration rules, you click a leaf node on the Policy Tree. Once you select a leaf node, you can click the matching rules and acceleration rules on the menu bar to view specific rule parameters for each node.
Each leaf node on the Policy Tree contains specific matching rules to which the WebAccelerator system matches incoming requests, (as described in Understanding 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 on the Policy Tree. Once the WebAccelerator system has matched an incoming request to a nodes matching rule, it applies that nodes corresponding acceleration rules.
The WebAccelerator system performs matching only against leaf nodes on the Policy Tree, and then applies the leaf nodes corresponding acceleration rules to the request. In contrast, the primary purpose of root and branch nodes is to help you easily configure and propagate the same acceleration rules to multiple leaf nodes. The WebAccelerator system cannot match requests and responses to a root node or a branch node on the Policy Tree.
The Policy Tree for this acceleration policy consists of the following two leaf nodes, configured with the specified matching rules.
A leaf node called Applications
The Application leaf node has two associated matching rules that identify a match for a CGI-based application as follows:
A leaf node called Images
The Images leaf node has an associated matching rule that identifies a match in a request, if the file extension is .gif.
For this acceleration policy, the WebAccelerator system matches requests to the Applications leaf node when the requests path is for a CGI-based application. Since the WebAccelerator system matches both requests and responses, if the response from the application on the origin web server is a GIF image, the WebAccelerator system matches the response to the Images leaf node and applies that leafs associated acceleration rules.
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. You can also change rule parameters at the leaf node level.
Figure 4.3 shows another example of a Policy Tree. For this Policy Tree, the acceleration policys rules are defined at the Home root node, and the Applications, Images, Documents, Components, and Other branch nodes inherit those rules, which is illustrated by the fact that nodes are a subset of the Home root node. Further, the Default, Search leaf nodes are a subset of the Application node, which means that these leaf nodes inherit the rules from Applications node.
In this case, the majority of the rules associated with the Home root node are applicable to the branch nodes, Applications, Images, Documents, Components, and Other with a few exceptions. The tree structure allows you to propagate the rules from the Home root to the Applications node, and then further refine the rules that are specific to the Default and Search leaf nodes.
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 branch node. To determine inheritance for a rule parameter, view the rule parameters inheritance icon.
For example, Figure 4.4 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 4.5.
You can refine inherited rules at the leaf node level by editing parameters and any associated options. Any changes that you make to override inherited settings for a rule parameter display with an override icon. The override icon displays only for the rule parameters at the current leaf node. To see the point at which the option was overridden, you can place the cursor over the override icon.
For the content assembly rule in Figure 4.6, all of the options are inherited from the branch node, except for the Enable MultiConnect option, which was disabled at the leaf node. This inheritance override is depicted by the inheritance icon with a red X, next to Enable MultiConnect and the message next to the Content Assembly Options menu that states that the there is an overridden inheritance on the (leaf) node.
To see if the current leaf node inherited an overridden option, click the parent node and view its rules. If no rule options were overridden at the parent node, the node appears as in Figure 4.7.
By following the rule all the way back to its grandparent, we see that all the rule options were 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 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 of 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 all or 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 on the Policy Tree, as required.
Important: You can edit only user-defined acceleration policies. You cannot edit pre-defined or signed acceleration policies.
Add
Use this option to add a new branch or leaf node.
For more information, see To add a new branch to the Policy Tree, and To add a new leaf node to the Policy Tree.
Rename
Use this option to edit a branch of leaf nodes name and description.
For more information, see To rename a node on the Policy Tree tree.
Delete
Use this option to delete a branch or leaf node.
For more information, see To delete a node on the Policy Tree.
Copy
Use this option to copy a branch or leaf node.
For more information, see To copy a node on the Policy Tree.
 
Up button, Down button
Use these options to move the priority of a leaf node up or down within the branch.
For more information, see To change the priority of a node on the Policy Tree.
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, where you can specify the matching rules and acceleration rules for the new branch as required.
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 rules 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.
You can change the priority of a leaf node only within a branch of the tree. For example, in Figure 4.3, you can give the Default leaf node priority over the Search leaf node, but not over the Images node.
2.
On the Policy Tree function bar, click the Up or Down button.
The node changes positions on 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, pre-defined, and signed 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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