Understandingiis 120715123909-phpapp01
- 2. Contents Web Server Kernel & User mode IIS and it's main components Different Modes of Operations Request Processing Take Away
- 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. Kernel & User Mode • The executing code • The executing code has complete and has no ability to unrestricted access directly access to the underlying hardware or hardware. reference memory. • Kernel mode is • Code running in user generally reserved mode must delegate for the lowest-level, to system APIs to most trusted access hardware or functions of the memory. operating system.
- 5. Kernel & User Mode • Crashes in kernel • Crashes in user mode mode are are always catastrophic; they recoverable. will halt the entire PC. • Comparatively slow • Usually work faster, as they have to ask because, as part of the system the the system, it can permission to use directly use all the more memory or hardware resources more CPU resources. it needs.
- 6. IIS & it's 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. 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. 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. 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. ISAPI Application Mapping are implemented as DLLs that • ISAPI extensions 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. 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
- 12. DLLHost.exe (IIS 5.0) • Manage out-of-process ISAPI applications • Any pooled ISAPI applications running on the server run within the context of a single instance of DLLHost.exe • The dllhost.exe process goes by the name COM Surrogate, which is an general purpose executable to host dlls out of process • In case of any unhandled error which may crash the COM Surrogate process, leaves the originating process intact.
- 13. Application Pools (IIS 6.0) • 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. IIS Different Modes of Operations • IIS 5.0 isolation mode (InetInfo.exe or DLLHost.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. IIS 5.0 Isolation Mode file:///C:/Documents and Settings/Admin/My Documents/My Pictures/iis5_isolation_mode.jpg
- 16. 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.
- 17. IIS 6.0 Isolation Mode file:///C:/Documents and Settings/Admin/My Documents/My Pictures/iis6_isolation_Mode.jpg
- 18. 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.
- 19. Request Processing(contd.) • 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.
- 20. Take Away