For the past few years while interacting with developers in the .NET community I have seen that they are very much conversant with language (C#) and ASP.NET features.But very few of them has a clear idea about idea about how IIS works and the ASP.NET Request Pipeline.So in this blog and subsequent blogs I will covering some key aspects of II6.0 and ASP.NET Request processing model.
IIS Web Site
The first important unit of IIS 6.0 Infrastructure is the IIS Web Site.A IIS Web Site is configured to listen to incoming HTTP requests
- Directed to a particular IP address or port number(http://127.0.01:7018 )
- Directed using a specific host header(e.g. http://xyz.com)
By default IIS created an web site named Default Website and configured to listen on port 80.Additional sites can be configured using the IIS Administration tool.
IIS Virtual Directory
Every IIS Website maps to a physical folder in the server.The Default Website maps to C:\Inetpub\wwwroot folder by default.A virtual directory within a site is a container of files and defines a child URL space within the website e.g. If we create a virtual directory called Chat within the website www.xyz.com then it can be accessed as http://www.xyz.com/Sales .We can map this virtual directory to a physical folder named D:\Chat in the server.
IIS Application or Virtual Application
In IIS 6.0 the terms application and virtual directory is bit confusing and is found to be used interchangeably in many tech articles.An application can be considered as a virtual directory with a additional properties like Application Name,Application Root(Starting Point),Application Pool ID.The Web Site by default is associated with an application even if the above mentioned properties are not specfically set.An application should have at least one virtual directory.It can also have more than one virtual directories.e.g The WebSite www.xyz.com can contain a virtual directory as well as application named Chat (www.xyz.com/Chat) and within the application Chat there can be another virtual directory Messages (http://www.xyz.com/Chat/Messages). This virtual directory may not be an application .
An application pool is a mechanism to group and isolate a set of web applications hosted by the IIS server.Each web application is assigned to one application pool.Each application pool runs in the different instance of the worker process(w3wp.exe).e.g. there is WebApp A assigned to AppPool AP1 and WebApp B assigned to App Pool AP2 then WebApp A and B runs in two seperate processes executing different instances of w3wp.exe.This ensures better application isolation and protection i.e. failure of any one the applications will not hamper the execution of the other.Application Pool identity is the identity under which the application pool worker process executes.By default this is the network service account.This can be changed and configured using the IIS Admin Tool.The other important configurations include the application pool health monitoring and worker process recycling.The details are provided in IIS documentation http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/f05a7c2b-36b0-4b6e-ac7c-662700081f25.mspx?mfr=true