Introduction
Web servers are computers that serve up Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://www.Example.com/index.html in your browser, this sends a request to the Web server whose domain name is Example.com. The server then fetches the page named index.html and sends it to your browser.
Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others
IIS (Internet Information Services) is a web server application created by Microsoft for use with Microsoft Windows. It is used to host your ASP.NET Web application. IIS has its own ASP.NET Process Engine to handle the ASP.NET request. So, when a request comes from client to server, IIS takes that request and process it and send response back to clients.
When we run our ASP.NET Web Application from visual studio IDE, VS Integrated ASP.NET Engine is responsible to execute all kind of asp.net requests and responses. The process name is “WebDev.WebServer.Exe” which actually take care of all request and response of an web application which is running from Visual Studio IDE.
When client request for some information from a web server, request first reaches to HTTP.SYS of IIS. HTTP.SYS then send the request to respective Application Pool. Application Pool then forward the request to worker process to load the ISAPI Extension which will create an HTTPRuntime Object to Process the request via HTTPModule and HTTPHanlder. After that the ASP.NET Page LifeCycle events starts.
Useful Things to know
There are two terms which are really useful while understanding how IIS server process ASP .NET requests
1. Worker Process
2. Application Pools
1. Worker Process
The "Process" which is responsible for processing Asp.net application request and sending back response to the client , is known as "Worker Process". All ASP.NET functionalities runs within the scope of this process.
All the ASP.Net functionality runs under the scope of worker process. When a request comes to the server from a client worker process is responsible to generate the request and response. In a single word we can say worker process is the heart of ASP.NET Web Application which runs on IIS.
Useful Things to know
There are two terms which are really useful while understanding how IIS server process ASP .NET requests
1. Worker Process
2. Application Pools
1. Worker Process
The "Process" which is responsible for processing Asp.net application request and sending back response to the client , is known as "Worker Process". All ASP.NET functionalities runs within the scope of this process.
All the ASP.Net functionality runs under the scope of worker process. When a request comes to the server from a client worker process is responsible to generate the request and response. In a single word we can say worker process is the heart of ASP.NET Web Application which runs on IIS.
2. Application Pool
Application pool is the container of worker process. Application pools is used to separate sets of IIS worker processes that share the same configuration. Application pools enables a better security, reliability, and availability for any web application. The worker process serves as the process boundary that separates each application pool so that when one worker process or application is having an issue or recycles, other applications or worker processes are not affected. This makes sure that a particular web application doesn’t not impact other web application as they are configured into different application pools.
An Application Pool can contain one or more applications and allows us to configure a level of isolation between different Web applications. For example, if you want to isolate all the Web applications running in the same computer, you can do this by creating a separate application pool for every Web application and placing them in their corresponding application pool. Because each application pool runs in its own worker process, errors in one application pool will not affect the applications running in other application pools. Deploying applications in application pools is a primary advantage of running IIS 6.0 in worker process isolation mode because you can customize the application pools to achieve the degree of application isolation that you need.
Application pool is the container of worker process. Application pools is used to separate sets of IIS worker processes that share the same configuration. Application pools enables a better security, reliability, and availability for any web application. The worker process serves as the process boundary that separates each application pool so that when one worker process or application is having an issue or recycles, other applications or worker processes are not affected. This makes sure that a particular web application doesn’t not impact other web application as they are configured into different application pools.
An Application Pool can contain one or more applications and allows us to configure a level of isolation between different Web applications. For example, if you want to isolate all the Web applications running in the same computer, you can do this by creating a separate application pool for every Web application and placing them in their corresponding application pool. Because each application pool runs in its own worker process, errors in one application pool will not affect the applications running in other application pools. Deploying applications in application pools is a primary advantage of running IIS 6.0 in worker process isolation mode because you can customize the application pools to achieve the degree of application isolation that you need.
Note: Application Pool with multiple worker process is called “Web Garden”.
How IIS Process ASP .NET Requests
IIS process the request when a new request comes up from client. If we look into the IIS 6.0 Architecture, we can divided them into Two Layer
1. Kernel Mode
2. User Mode
Now, Kernel mode is introduced with IIS 6.0, which contains the HTTP.SYS. So whenever a request comes from Client to Server, it will hit HTTP.SYS First.
IIS process the request when a new request comes up from client. If we look into the IIS 6.0 Architecture, we can divided them into Two Layer
1. Kernel Mode
2. User Mode
Now, Kernel mode is introduced with IIS 6.0, which contains the HTTP.SYS. So whenever a request comes from Client to Server, it will hit HTTP.SYS First.
Now, HTTP.SYS is Responsible for pass the request to particular Application pool. Now here is one question, How HTTP.SYS comes to know where to send the request? This is not a random pickup. Whenever we create a new Application Pool, the ID of the Application Pool is being generated and it’s registered with the HTTP.SYS. So whenever HTTP.SYS Received the request from any web application, it checks for the Application Pool and based on the application pool it send the request.
So, this was the first steps of IIS Request Processing.
Till now, Client Requested for some information and request came to the Kernel level of IIS means at HTTP.SYS. HTTP.SYS has been identified the name of the application pool where to send. Now, let’s see how this request moves from HTTP.SYS to Application Pool.
In User Level of IIS, we have Web Admin Services (WAS) which takes the request from HTTP.SYS and pass it to the respective application pool.
Till now, Client Requested for some information and request came to the Kernel level of IIS means at HTTP.SYS. HTTP.SYS has been identified the name of the application pool where to send. Now, let’s see how this request moves from HTTP.SYS to Application Pool.
In User Level of IIS, we have Web Admin Services (WAS) which takes the request from HTTP.SYS and pass it to the respective application pool.
When Application pool receive the request, it simply
pass the request to worker process (w3wp.exe) . The worker process “w3wp.exe”
looks up the URL of the request in order to load the correct ISAPI extension.
ISAPI extensions are the IIS way to handle requests for different resources.
Once ASP.NET is installed, it installs its own ISAPI extension
(aspnet_isapi.dll) and adds the mapping into IIS.
When Worker process loads the aspnet_isapi.dll, it start an HTTPRuntime, which is the entry point of an application. HTTPRuntime is a class which calls the ProcessRequest method to start Processing.
When this methods called, a new instance of HTTPContext is been created. Which is accessible using HTTPContext.Current Properties. This object still remains alive during life time of object request. Using HttpContext.Current we can access some other objects like Request, Response, Session etc
After that HttpRuntime load an HttpApplication object with the help of HttpApplicationFactory class.. Each and every request should pass through the corresponding HTTPModule to reach to HTTPHandler, this list of module are configured by the HTTPApplication.
Now, the concept comes called “HTTPPipeline”. It is called a pipeline because it contains a set of HttpModules ( For Both Web.config and Machine.config level) that intercept the request on its way to the HttpHandler. HTTPModules are classes that have access to the incoming request. We can also create our own HTTPModule if we need to handle anything during upcoming request and response.
HTTP Handlers are the endpoints in the HTTP pipeline. All request that are passing through the HTTPModule should reached to HTTPHandler. Then HTTP Handler generates the output for the requested resource. So, when we requesting for any aspx web pages, it returns the corresponding HTML output.
All the request now passes from httpModule to respective HTTPHandler then method and the ASP.NET Page life cycle starts. This ends the IIS Request processing and the ASP.NET Page Lifecycle.
When this methods called, a new instance of HTTPContext is been created. Which is accessible using HTTPContext.Current Properties. This object still remains alive during life time of object request. Using HttpContext.Current we can access some other objects like Request, Response, Session etc
After that HttpRuntime load an HttpApplication object with the help of HttpApplicationFactory class.. Each and every request should pass through the corresponding HTTPModule to reach to HTTPHandler, this list of module are configured by the HTTPApplication.
Now, the concept comes called “HTTPPipeline”. It is called a pipeline because it contains a set of HttpModules ( For Both Web.config and Machine.config level) that intercept the request on its way to the HttpHandler. HTTPModules are classes that have access to the incoming request. We can also create our own HTTPModule if we need to handle anything during upcoming request and response.
HTTP Handlers are the endpoints in the HTTP pipeline. All request that are passing through the HTTPModule should reached to HTTPHandler. Then HTTP Handler generates the output for the requested resource. So, when we requesting for any aspx web pages, it returns the corresponding HTML output.
All the request now passes from httpModule to respective HTTPHandler then method and the ASP.NET Page life cycle starts. This ends the IIS Request processing and the ASP.NET Page Lifecycle.
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