IIS

1. What is Web Server ?

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  web application which is running from Visual Studio IDE.
Now, the name “Web Server” comes into picture when we want to host the application on a centralized location and wanted to access from many locations. Web server is responsible for handle all the requests that are coming from clients, process them and provide the responses.

2. What is IIS ?

IIS (Internet Information Server) is one of the web servers from Microsoft that is used to host your ASP.NET Web application. IIS has it’s 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.

3. What is Worker Process?
An Internet Information Services (IIS) worker process is a windows process (w3wp.exe) which runs Web applications, and is responsible for handling requests sent to a Web Server for a specific application pool.
This process is responsible to manage all the request and response that are coming from client system.  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.
4. What is Application Pool?
An Internet Information Services (IIS) application pool is a grouping of URLs that is routed to one or more worker processes. Because application pools define a set of Web applications that share one or more worker processes, they provide a convenient way to administer a set of Web sites and applications and their corresponding worker processes. Process boundaries separate each worker process; therefore, a Web site or application in one application pool will not be affected by application problems in other application pools. Application pools significantly increase both the reliability and manageability of a Web infrastructure.
OR 
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.
5. What is Web Farm?
This is the case where you have only one web server and multiple clients requesting for resources from the same server. But when there is huge amount of incoming traffic for your web sites, one standalone server is not sufficient to process the request. You may need to use multiple servers to host the application and divide the traffic among them. This is called “Web Farm”. So when you are hosting your single web site on multiple web servers over load balancer is called “Web Farm”.

Advantages of Web Farm

  • It provides high availability. If any of the servers in the farm goes down, Load balancer can redirect the requests to other servers.
  • Provides high performance response for client requests.
  • Provides better scalability of the web application and reduces the failure of the application.
  • Session and other resources can be stored in a centralized location to access by all the servers.

6. What is Web Garden?
when we are talking about requesting processing within IIS, Worker Process (w3wp.exe) takes care of all of these. Worker Process runs the ASP.NET application in IIS. All the ASP.NET functionality inside IIS runs under the scope of worker process. Worker Process is responsible for handling all kinds of request, response, session data, cache data. Application Pool is the container of worker process. Application pool is used to separate sets of IIS worker processes and enables a better security, reliability, and availability for any web application.
Now, by default, each and every Application pool contains a single worker process. Application which contains the multiple worker process is called “Web Garden”.

Advantages of Web Garden

  • Provides better application availability by sharing requests between multiple worker process.
  • Web garden uses processor affinity where application can be swapped out based on preference and tag setting.
  • Less consumption of physical space for web garden configuration.

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