If you are debugging a ASP.NET web application which is hosted on IIS, you need to attach the particular worker process in Visual Studio to start debugging. To Attach a process we can go to Tools > Attach Process or use shortcut key Ctrl +P. The process window will show the worker process (w3wp.exe) which is currently running on IIS. You need to select the process and click on attach button to start the debugging.
Problem starts when you have multiple worker process running on IIS.  If you have multiple sites hosted on IIS and each site having their own application pool then you will see the list of all worker process in the Process Attach window.

Here  you need to identify the particular worker process which is associated with your application pool.

Note: Whenever we create a new Application Pool, the ID of the Application Pool is being generated and it’s registered with the HTTP.SYS (Kernel Level of IIS) . 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

To know more about IIS Request Process, here is one of my aticle How IIS Process ASP.NET Request

Identify Worker Process in IIS 6.0

• Start > Run > Cmd
• Go To Windows > System32
• Run cscript iisapp.vbs
• You will get the list of Running Worker ProcessID and the Application Pool Name.

So, here is your list of all worker process with corresponding application pool name.  From  the Application pool name you can easily identify which worker process is related with your application.

Identify Worker Process in IIS 7.0

From IIS 7.0 you need you to run IIS Command Tool ( appcmd ) .
• Start > Run > Cmd
• Go To Windows > System32 > Inetsrv
• Run appcmd list wp

This will show you list worker process that is running on IIS 7.0 in the similar format of IIS 6.0

List of IIS Article Published by Me

Beginner’s Guide : Exploring IIS 6.0 With ASP.NET
Debug Your ASP.NET Application that Hosted on IIS : Process Attach and Identify which process to attach
Remote IIS Debugging : Debug your ASP.NET Application which is hosted on “Remote IIS Server”
How IIS Process ASP.NET Request

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