SAS/IntrNet 9.2: Application Dispatcher

An Overview of the Application Dispatcher

Using the Application Dispatcher, you can send information from a Web browser to a SAS session for processing and receive the results on your Web browser. The results can appear as text, HTML, GIF, JPEG, or any other format that is supported by your Web browser.

By submitting an HTML form or clicking a hypertext link, you can cause SAS to run a program. The program can be written by you or someone else at your site, or it can be a sample program that is provided by SAS. You can even use the sample forms and code as the foundation for your own applications. You can easily modify almost any SAS batch program to run on the Web and thus add new life to legacy applications and legacy data. Some commercial SAS applications that run by using the Application Dispatcher are included with SAS/IntrNet software.

To get started with Application Dispatcher terminology and concepts, read the following:

What Is the Application Dispatcher?

The Application Dispatcher exchanges and processes information by using the following components:

The input component runs on the Web server or the client. It normally consists of static or dynamically generated HTML pages containing URL references or HTML forms. The input component is responsible for selecting what program component to run and what input data to pass to that program component.

The Application Broker is a CGI program that resides on your Web server (for example, in the cgi-bin or scripts directory). The Application Broker interprets the information received from the input component and passes it to the Application Server.

The Application Server is a SAS session that receives input from the Application Broker. The Application Server accepts information from the Application Broker CGI program and invokes the program component.

The program component is a SAS program invoked within the Application Server. The program

receives the request from the server
processes it
returns the results to the Application Broker for delivery to the Web browser and the waiting user.

What Are Application Dispatcher Services?

Each request from the Web browser contains the name of a service that will fulfill the request. The Application Broker identifies the service by looking into its configuration file and then determines where and how the request should be forwarded. The configuration file defines the three services (socket, launch, and pool) that are available for Application Dispatcher applications to use.

A socket service runs the Application Server continuously, waiting for new requests, and refers to the protocol that is used (TCP/IP sockets) to communicate between the server and the Application Broker. Using this type of service, many servers can run at the same time, letting the Application Broker balance the load. As multiple users invoke Application Dispatcher programs, multiple servers can be used to improve application performance. An optional component called the Application Load Manager can be added to assist the Application Broker in balancing the load.

Instead of using the socket service method of running the Application Server, you can use the launch service, which starts a new server for each request. Although this method can require more time than the socket service because of the Application Server start-up time, it is easier to administer and provides some security advantages.

Using the Application Load Manager, the pool service starts servers from the pool as needed to handle queued jobs. When a job completes, the server becomes available for new requests until an optional idle time-out is reached, at which time the server shuts down.

What Are Application Dispatcher Applications?

The Application Broker and the Application Server provide the communication and processing mechanisms for Application Dispatcher applications. An Application Dispatcher application consists of one or more associated input components and program components. The program components for an Application Dispatcher application can be any of the following:

a SAS program (an external file that has a .sas extension)
a source entry (a catalog entry that has a .source extension)
an SCL entry (a catalog entry that has a .scl extension)
a compiled macro (a catalog entry that has a .macro extension).

The program component that you create must be designed to accept the information that is received from the Web browser. In many cases, this means that you not only create the source program but also the HTML page that passes information to the Application Broker.

What Is the Application Load Manager?

The Application Load Manager (LOADMGR) is a separate, optional process that can be used to enhance the distribution of Application Dispatcher resources on a network. If installed, it records the state of all Application Servers and maintains a separate dynamic pool of available servers. These capabilities enable the Load Manager to distribute Application Dispatcher requests most efficiently.

The Load Manager is of greatest use to the person who creates and maintains the configuration file for the Application Broker.

Who Uses the Application Dispatcher?

You should use the Application Dispatcher if you

want to analyze and display information dynamically on the Web and let your Web users immediately retrieve the information they need.
have SAS programming experience but have little or no CGI programming experience. Application Dispatcher enables you to create the Web user interface and retrieve the SAS data for display on the Web without writing a CGI script.
want to create applications that provide Web output without investing a lot of programming time.
want to create applications that run on a variety of Web browsers.

The Application Dispatcher has several types of users:

End users enter information in a form, select a link, or view an inline image that displays in a Web browser.
Web-page authors create the HTML forms or pages, which include unique Application Dispatcher fields. These individuals could be SAS application developers.
Application Dispatcher program developers create the Application Dispatcher programs that receive information entered on the Web page.
System administrators, also known as Webmasters, maintain programs on the Web server or maintain the Application Server(s).

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