Migrating a Web Server to IIS 5.0

IIS 5.0 Application Technologies

The following is a brief description of the application technologies supported by IIS 5.0.

CGI IIS 5.0 fully supports both scripts and executables written to the CGI specification. IIS 5.0 supports scripts written in a variety of languages when the appropriate Win32 script interpreter is installed and configured, for example, Perl, Python, TCL, REXX, and JScript. It also supports scripts written in VBScript that have been modified to support standard input and output variables. As a result, many CGI applications can be ported to IIS 5.0 with minimal changes.
ISAPI Extensions ISAPI extensions consist of multithreaded DLLs loaded into IIS 5.0. ISAPI extensions have a strong performance advantage over CGI applications for several reasons. First, ISAPI extensions can be configured so all of them run in a single process, or so they run in the same memory space as the Web service. Second, instead of loading an executable for each request, ISAPI uses thread-safe DLLs that are loaded only once. Finally, ISAPI uses Win32-based APIs to communicate with the Web service, which is much faster than CGI methods. ISAPI extensions developed for other Web servers are generally easy to port to IIS 5.0. In addition, it is sometimes advantageous to rewrite existing CGI applications as ISAPI extensions to improve their performance, as discussed later in this section.
ISAPI Filters ISAPI filters extend the capabilities of IIS 5.0. You can write an ISAPI DLL to intercept specific server events and perform appropriate actions. This functionality is especially useful in implementing server security. For more information, see http://www.bnt.com/inetsdk/httpfilt.htm#_in_Overview.
ASP ASP is an open, server-application environment in which you can combine HTML, server-side scripts, and reusable COM components to create dynamic and powerful Web-based business solutions. IIS 5.0 natively supports scripts in ASP pages written in both VBScript and JScript, but you can use any scripting language when the appropriate script interpreter conforming to the Active Scripting standard is installed. ASP provides a number of intrinsic objects that make application development quick and easy, including Application, Session, Request, Response, and Server objects. ASP also supports COM components, which allow you to reuse business logic in other applications. ASP is supported by a number of Web servers, and existing ASP applications can be easily ported to IIS 5.0. In addition, it is often a good idea to rewrite CGI applications as ASP, as discussed later in this section, particularly those with functionality that you can quickly and easily reproduce by using ASP built-in objects.
Note The terms “CGI script” and “script in an ASP page” can be confusing. Generally, when people use the term “CGI script,” they are referring to a Perl script and then become mystified when this “CGI script” causes an ISAPI error. To ease the confusion, keep in mind that a script is simply a file containing instructions that are processed by some other component. A script in an ASP page, for example, might be a VBScript or a JScript file that is handed off to Asp.dll for processing. As with scripts in an ASP page, Perl scripts are handed off to a Perl interpreter for processing. However, some Perl interpreters are CGI-based executables and some are ISAPI-based DLLs—and the latter can create an ISAPI error.