Novell Documentation: Volera Excelerator 2.3 - Understanding URL Overrides

Understanding URL Overrides

The key mechanism that Excelerator uses to prepare internal content for exposure on the Internet is called the URL override.

URL overrides can be

Automatically created by Web Server Accelerator services and/or Secure Excelerator.
Manually specified by administrators using the URL Override Dialog Box.

For more information regarding automatically and manually created URL overrides, see Automatic Vs. Manual URL Overrides.

Secure Excelerator: The All-in-One Solution

Secure Excelerator solves each of the issues identified in Identifying the Issues using SSL version 3 technology to protect your sensitive data and transform embedded object links. It does not require any additional software or special configuration of either your Web servers or the browsers accessing your Web site.

The product was specifically designed for e-businesses, enterprises, and other organizations that want to conduct business using the Web.

For more information on obtaining and installing Secure Excelerator, see the Volera Secure Excelerator 1.1 Administration Guide.

URL Overrides Transform Object Reference URLs in Cached HTML

The base Excelerator product and Secure Excelerator both use URL overrides to address security and object embedding issues by transforming content before it is cached. Specifically, URL overrides affect one or more of the following fields in object reference URLs in the HTML:

DNS Name Overrides: These change each instance of the origin Web server's DNS hostname when it appears in an object reference URL within the HTML. The override changes the origin Web server's DNS name to the DNS name of the accelerator service to which the override belongs (if the two DNS names are different).
Port Overrides: When the object reference URL includes a port number with the origin server's DNS name, port overrides change the port number of the origin Web server to the port numbers of the accelerator service (assuming the two ports are different).
Pathrule: Excelerator's path-based multihoming option uses pathrule overrides to let parent accelerator services know which child accelerator service has file in the object reference URL.
Protocol Scheme: Secure Excelerator uses scheme overrides to change the HTML protocol scheme from HTTP to HTTPS when vending the objects on the Internet.

Automatic Vs. Manual URL Overrides

Understanding when to create manual URL overrides requires that you clearly understand when the system creates automatic overrides.

Understanding When Automatic URL Overrides Are Created

URL overrides are automatically created by Web Server Accelerators and Secure Excelerator as indicated in the following table:

Table 19.

Object Reference URL Component	Trigger for Automatic Override Creation	How the Override Works
DNS Name	If the accelerator service's DNS Name is different from the origin Web server's DNS name listed in the Web Server Addresses list, the system automatically creates a DNS name override for the service that covers references to objects cached on the service. Usually the origin Web server's DNS name is used in internal browser requests, and the accelerator service's DNS name is used in requests coming from the Internet. IMPORTANT: If the origin Web server's name entry is the server's IP address, an automatic DNS Name override is not created.	Prior to caching an HTML object for the service, the DNS name override changes all object references that contain the origin Web server's DNS name, replacing it with the DNS Name specified for the accelerator service. Since DNS servers on the Internet have no knowledge of internal DNS names, this action ensures that a DNS server on the Internet can properly resolve browser requests for objects whose URLs have been changed to contain the correct, Internet DNS name.
Port	If the Web Server Port and the Accelerator Proxy Port fields are different in the accelerator service definition, the system automatically creates a port override for the service that covers references to objects on the origin Web server. Sometimes, internal networks use non-standard port numbers. For example, the internal HTTP port number might be 81 instead of 80. IMPORTANT: If you are using Secure Excelerator, the port override is specified in the Secure Excelerator Options dialog box.	Prior to caching an HTML object for the service, the port override changes all references in the HTML that point to the accelerated Web server and contain the Web Server Port value specified, replacing the Web Server Port value with the Accelerator Proxy port value specified. This action ensures that the request is routed using the correct port. NOTE: In the case of port overrides, if the accelerator proxy port value is the industry standard port number, the URL override simply removes the port number from the URL.
Pathrule	If path-based multihoming is enabled for a child accelerator service and a starts-with rule is specified for the Sub-Path Match String, the system automatically creates a pathrule override for the service.	Prior to caching an HTML object, the pathrule override changes all object reference URLs that point to the accelerated Web server by inserting the Sub-Path Match String at the root of the URL path. When the parent accelerator service gets a browser request from the Internet with the Sub-Path Match String embedded, the parent accelerator service knows the request must be routed to the child accelerator service.
Protocol Scheme	If Secure Excelerator is installed and enabled for the service, the system automatically creates a scheme override for the service.	Prior to caching an HTML object, the scheme override changes all object reference URLs in the HTML that point to the accelerated Web server by changing the protocol scheme from HTTP to HTTPS.

Understanding When to Create Manual URL Overrides

The key point to remember when deciding whether a manual override is required is that automatic overrides apply only to objects that originate on the origin Web server from which the accelerator service fills content. Object reference URLs that point to other origin Web servers are not changed.

The following table can help you decide whether you need to create any manual overrides:

Table 20.

Object Reference Component	A Manual Override is Required If
DNS Name	The origin Web server for an accelerator service contains object reference URLs that point to objects on another origin Web server that is being accelerated by another accelerator service. and The DNS names in the other object reference URLs must be changed for the references to resolve correctly on the Internet. IMPORTANT: You will also need to create a manual DNS Name override if an override is required and the origin Web server's DNS name is an IP address because the system will not create an automatic override in that case.
Port	The origin Web server for an accelerator service contains object reference URLs that point to objects on another origin Web server that is being accelerated by another accelerator service. and The port number in the other object reference URLs must be changed for the references to resolve correctly on the Internet.
Pathrule	References to objects on a child service occur on either the parent service or on one of the other child services. (References to objects on a given child service are automatically changed only on that child service. References to the given child service from the parent service or other children are not changed unless you create a manual URL override.)
Protocol Scheme	The origin Web server for a Secure-Excelerator-enabled accelerator service contains object reference URLs that point to objects on other accelerated origin Web servers (whether or not they have Secure Excelerator enabled.