This is a reply i got from Ravish Kumar Singh
Hi jini jane,
Its not like that I am very knowledegable, but still I will try to answer
your question.
Actually I also had the same problem in understanding the web server and app
server.
And my understanding is:
Web Server: Web server is a server basiaclly which implements HTTP protocol
to communicate with other clients who also implements HTTP protocol for
contacting the server. Server's example which are coming to my mind is you
can think of old version of PWS(Personal web servers), in truly sense they
were web server, whose job was to listen request and send back the required
resource(most of the time plain html files), if available on server.
OK, first let us see what is URL. URL is consist of
Protocol://DomainName/resourcePath/resource Example:
http://www.myDomain.com/myFolder/myfile.html Client examples are IE, netscape.. and other internet browsers.
We can also compare this with restaurant industry where waiter's job is to
take order and serve it. Customer is client who is looking for some
resource.
Now let us see application server. Application server is, if we again
consider our example is Cook in restaurant. Now customer orders for coffee,
waiter takes the order, forward it to cook, cook makes coffee give back to
waiter to server it to the customer. Now server is not aware of cook, he can
see only waiter. If customar wants to communicate with restaurant(i.e. web
application), the only way is waiter.
Now if coffee is already made by someone and available in restaurant, we
dont need cook. But customer might get cold coffee instead of hot.
I hope by now web server and app server difference is clear.
Now, a waiter cant make coffee but a cook can. Now if cook is working as
waiter also, I mean if he is taking order/request and making coffe also he
is working as both, I mean web server and app server.
Now in todays era, there is very thin line between web server and app
server, all app server(cook) are also web server(waiter).
Now let us see your second prob:
Servlet engine resides in a app server. When a request comes webserver
listens it if the request is suppose to be paased to app server it passes it
to app server. Now app server decides what to do with the request and most
of the time he has to do some computation or something. So app will invoke
servlet engine.
And as I said now days there is very thin line between web server and app
server.
Now last but not least, even though cook is also working as waiter but its
not necessary that he will go in kitchen for all orders. Some customer might
ask water for which he does not need to go to kitchen. So though he is cook
but still at that time he is totally working as waiter, but it is a very
less price for what he is saving by not giving monthly pay to waiter.
hmmmmm... I hope you understand all this, whatever I wrote.
AW HTH
All the best
Ravish K Singh
[ November 27, 2002: Message edited by: jini jane ]
