“Understanding our IIS - Part1”

Remember This?

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)

IIS• IIS fulfills the role of Web Server, responding

to request for files and logging activity.• IIS maintain the info about

– The location of the content files– What security identities have access– How content files are separated in apps– Provides what URLs are mapped to

those apps• IIS Administrative Tools helps you to make

web content creation fast and easy

IIS Components• Kernel Mode

– HTTP.sys• User Mode

– WWW Service– Worker processes (W3wp.exe)– ISAPI– ISAPI Components (Extensions &

Filters)– Application Pools

Remember This Again?

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.

WWW Service• Also known as “W3Svc”or“Svchost.exe”• It manages the IIS metabase

(Metabase.bin) + monitors W3p.exe• Metabase is a config file for IIS (like a

registry) available for other apps• Manages application pools and starting,

stopping and recycling w3c process• WWW Service also collect the counters

for Web sites

W3wp.exe• A worker process is user-mode code whose role

is to process requests, such as processing requests to return a static page

• 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.

• Multiple W3wp.exe can run for a single website• Each worker process internally use ISAPI

Extensions and Filters

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 while filters are local to IIS used to put checkpoints for incoming/outgoing data

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

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

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

IIS 6.0 Isolation Mode

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.

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.

And thus we welcome