Understanding IIS


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Lets understand the Internet Information Services better by knowing the main components and peep into the different architecture

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Understanding IIS

  1. 1. “Understanding our IIS”
  2. 2. Contents  Web Server  Kernel & User mode  IIS and it's main components  Different Modes of Operations  Request Processing  Take Away
  3. 3. Web Server • The primary function of a web server is to deliver web pages on requests from clients using HTTP. • It can be referred as hardware(computer) or the software (computer application) • Hosts websites/web application to serve www. • Found embedded in devices like printers, routers, web-cams to serve local network • Able to map URL to a local file system resource (static requests) as well as internal or external program name (dynamic requests)
  4. 4. Kernel & User Mode • The executing code has complete and unrestricted access to the underlying hardware. • Kernel mode is generally reserved for the lowest-level, most trusted functions of the operating system. • The executing code has no ability to directly access hardware or reference memory. • Code running in user mode must delegate to system APIs to access hardware or memory.
  5. 5. Kernel & User Mode • Crashes in kernel mode are catastrophic; they will halt the entire PC. • Usually work faster, because, as part of the system, it can directly use all the hardware resources it needs. • Crashes in user mode are always recoverable. • Comparatively slow as they have to ask the system the permission to use more memory or more CPU resources.
  6. 6. IIS main components • Designed to provide secure, scalable solutions for creating and managing www sites and servers • We can publish information on intranets, extranets and the internet • Provides FTP, SMTP, Indexing and other services • Components: – HTTP.sys – Worker processes (W3wp.exe) – ISAPI – InetInfo.exe – Application pools
  7. 7. HTTP.sys • Also known as “HTTP Protocol Stack” or “Http Listener Process” • Implemented as a kernel-mode device driver • core component to receive and serve HTTP requests and passing them off to the worker processes • When you create a Web site, IIS registers the site with HTTP.sys • Other than retrieving a stored response from its internal cache, HTTP.sys does not process the requests that it receives.
  8. 8. W3wp.exe • A worker process is user-mode code whose role is to process requests, such as processing requests to return a static page • The worker process is controlled by the WWW service • A worker process runs as an executable file named W3wp.exe • Worker processes also run application code, such as ASP.NET applications and XML Web services.
  9. 9. ISAPI • Internet Server Application Programming Interface, is an API developed to provide the application developers with a powerful way to extend the functionality of IIS • Extensions and Filters are the two types of applications that can be developed using ISAPI • ISAPI extensions are true applications that run on IIS and have access to all of the functionality provided by IIS
  10. 10. ISAPI Extensions • ISAPI extensions are implemented as DLLs that are loaded into a process that is controlled by IIS • Like ASP and HTML pages, IIS uses the virtual location of the DLL file in the file system to map the ISAPI extension • ASP.Net functionality is contained in an ISAPI extension called aspnet_isapi.dll • Any file that is requested from the IIS server that ends in “.aspx” is mapped to aspnet_isapi.dll which is assigned to process the file before displaying its output in the client’s window
  11. 11. ISAPI Filters • ISAPI filters are DLL files that can be used to modify and enhance the functionality provided by IIS • ISAPI filters always run on an IIS server, filtering every request until they find one they need to process • Mostly used for Authentication and Encryption of the i/p or o/p data for a site locally or all the apps globally
  12. 12. InetInfo.exe • A user-mode component that hosts the IIS metabase and that also hosts the non-Web services like the FTP, SMTP etc • Used to manage ISAPI applications that run within the IIS process context • The services that run in Inetinfo.exe run as dynamic-link libraries (DLLs) under the Local System account • In IIS5.0 or IIS6.0 runs in IIS5.0 isolation mode >Inetinfo.exe hosts the worker process
  13. 13. Application Pools • Group of Web Applications and Web Sites are called Application Pools • Every application within an application pool shares the same worker process • The worker process(w3wp.exe) that services one application pool is separated from the worker process that services another • Each separate worker process provides a process boundary so each application pool is separated by these process boundaries
  14. 14. IIS Different Modes of Operations • IIS 5.0 isolation mode (InetInfo.exe takes the ownership for request processing) • IIS 6.0 worker process isolation mode (worker process W3wp.exe takes the ownership for request processing)
  15. 15. Request Processing • A request arrives. If the requested application is running in- process, then Inetinfo.exe takes the request. If not, then DLLHost.exe takes the request. • Inetinfo.exe or DLLHost.exe determines if the request is valid. If the request is not valid, it sends a code for an invalid request back to the client. • If the request is valid, Inetinfo.exe or DLLHost.exe checks to see if the response is located in the IIS cache. • If the response is in the cache, it is returned immediately. • If the response is not cached, Inetinfo.exe or DLLHost.exe processes the request, by evaluating the URL to determine if the request is for static (HTML), or dynamic content (ASP) • The response is sent back to the client and the request is logged, if IIS is configured to do so.
  16. 16. IIS 6.0 Isolation Mode
  17. 17. Request Processing • A request arrives at HTTP.sys. • HTTP.sys determines if the request is valid. If the request is not valid, it sends a code for an invalid request back to the client. • If the request is valid, HTTP.sys checks to see if the request is for static content (HTML) because static content can be served immediately. • If the request is for dynamic content, HTTP.sys checks to see if the response is located in its “kernel-mode cache”. • If the response is in the cache, HTTP.sys returns the response immediately. • If the response is not cached, HTTP.sys determines the correct “request queue”, and places the request in that queue.
  18. 18. Request Processing • If the queue has no worker processes assigned to it, HTTP.sys signals the WWW service to start one. • The worker process pulls the request from the queue and processes the request, evaluating the URL to determine the type of request (ASP, ISAPI, or CGI). • The worker process sends the response back to HTTP.sys. • HTTP.sys sends the response back to the client and logs the request, if configured to do so.
  19. 19. Take Away