WORKING WITH IIS

Working with IIS:

• IIS (Internet Information Server) is a group of Internet servers (including a Web or Hypertext Transfer Protocol server and a File Transfer Protocol server) with additional capabilities for Microsoft's Windows NT and Windows 2000 Server operating systems.
• With IIS, Microsoft includes a set of programs for building and administering Web sites, a search engine, and support for writing Web-based applications that access databases.
  A typical company that buys IIS can create pages for Web sites using Microsoft's Front Page product (with its WYSIWYG user interface).
• Web developers can use Microsoft's Active Server Page (ASP)technology, which means that applications - including ActiveX controls - can be embedded in Web pages that modify the content sent back to users.
• Developers can also write programs that filter requests and get the correct Web pages for different users by using Microsoft's Internet Server Application Program Interface (ISAPI) interface.
• ASPs and ISAPI programs run more efficiently than common gateway interface (CGI) and server-side include (SSI) programs, two current technologies.
  Microsoft includes special capabilities for server administrators designed to appeal to Internet service providers (ISPs). 
• It includes a single window (or "console") from which all services and users can be administered.
• It's designed to be easy to add components as snap-ins that you didn't initially install.
• The administrative windows can be customized for access by individual customers.
  Worker process isolation mode Provides an easy way to insulate Web applications from each other, so that problems with one Web application don't impact the other Web applications on Microsoft Internet Information Services (IIS).
• IIS 6.0 allows you to organize applications into application pools. Each application pool is a completely independent entity, served by one or more worker processes.
• Windows administrator will create a separate application pool for each Web application that the server hosts but a single application pool can host multiple application

How application pools can isolate IIS Web applications from each other?

• True isolation is possible because Windows differentiates between code that is running in kernel mode vs. code that is running in user mode.
• Windows runs core IIS components, such as HTTP.SYS and the WWW service, in kernel mode. Each application pool contains its own kernel-mode queue. 
• This means that HTTP.SYS is able to route inbound requests directly to a queue that is dedicated to a specific application pool, all within kernel mode.
• Application pools are separated from each other by process boundaries.
  Worker processes are dedicated to a specific application pool to actually service requests.
• If a failure occurs, it usually happens within a worker process.
• Worker processes are bound to particular application pools, a worker process failure will only affect the application in which it resides, but no others.
• IIS provides mechanisms for monitoring the health of a worker process. If a worker process fails, the process can be restarted without the end user even being aware of the failure.