Knowing the Difference Between Application Server and Web ServerTo understand the difference between a web server and application server we should start with the understanding of the web server. A web server can be a computer or a program which accepts the HTTP request from a client which is generally a web browser and provide HTTP response in the form of HTML documents with some other requested objects like images. As the complexity of a web application increases we realize the need of some kind of logical program which can help the application in handling the pressure of exchanging data as well as functionality with other applications in an effective and organized manner.
This logical program is basically a server program which supports the business logic and executes the commands generated by a web server. This is known as application server. Web server is actually a subset of application server i.e. application server can include web server in itself. In strict sense a web server serves static HTML pages only. On the other hand application server handles database connections, lifecycle management, processing of dynamic web pages (by providing appropriate engines like servlet container for jsp and asp engine for ASP) and deploying the application. It would be interesting to understand the working of both which clearly distinguishes the role of both web server and application server in a web application. Whenever we request a web page from the server, we type the website name in the address bar of web browser. First of all web browser needs to know the IP address of the website name resolve to. For this it takes the help of one or more DNS servers which tells the browser at which IP address the website is located. After this browser request the website/webpage from the web server in the form of HTTP request. Server receives the request and responds by sending back the requested page and if the page does not exist or any other error occurs it provides the appropriate error message. A web server usually contains more than one website. In the above working we have discussed the case where the client request only static page. A different condition arises if the request of client needs some processing for example the need of dynamically generating flash application data or dynamically populating form elements etc. In that case web server passes the request to application server. As we know application server understands the business logic and can interpret the programming instructions, it generates an output understandable to browser and returns the result to web server which returns them to browser. So web server and application server both work together to fulfill the requirement of client depending upon the context and request nature.
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