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So let's talk about how Web applications work, and I'll tell you right now, I am not much of an artist,



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so my illustrations will not be great.



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But I'll tell you what I'm drawing as I draw them, otherwise you'll have no idea what it is.



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So let's start with the user.



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So we have a person right here.



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This is a person I told you I can't draw.



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And this person has a computer which I'll draw as a box.



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And this person wants to get to a website and the website is way over here somewhere.



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So I'm going to draw this as something that's not a box and that is a server.



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And this server has a Web site.



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So this person starts up their Web browser and they want to connect to this server over here on the



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right hand side of the screen.



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So they type in the URL.



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And the very first thing that happens is their computer goes off to a name server somewhere.



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So this is an S for a name server.



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And all that does is take an address like some sitcom and translate it into an IP address.



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And that IP address is unique for every device that's on the Internet.



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So this person over here has an IP address and so does the server.



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And the name server then sends back that IP address, which tells this machine, the user's computer,



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how to get to that server.



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So it sends a request.



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And that request is something as simple as show me the homepage for some site dotcom.



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So this server then does some magic behind the scenes.



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It might be just a static HTML page.



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And if that's all that it is, it just loads that page and all of the associated requests or images



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or whatever is in the page and sends it back to the user.



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But in a lot of cases, as will be the case for our project that will be building in this course, there's



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some magic that happens behind the scenes.



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So this server might have a database, it might have a cache, it might have some application that's



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running and these three things and there might be more than three.



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But these will actually do some magic to build that HTML.



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So it doesn't exist as a static file on the server somewhere.



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It actually builds the page and then sends that back after all sorts of magic happens behind the scenes.



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And this request from the user over here might send more than just a request.



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It might say, hey, here's a cookie and a cookie is just a little bit of data that has some information.



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It sends that along to the server saying this is who I am.



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Quite often you'll store information about a logged in user in a cookie, but you can store other things



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in there as well.



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So it will send that to the user, to the server.



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And the server says, oh, this is an authenticated user.



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So they have access to information that unauthenticated users might not have.



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So we'll send that back.



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And the server itself might also send instructions to the user saying, hey, build a cookie.



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For this request, so the first time this user authenticates, they might type in a username and password,



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the request goes way over the server.



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The server says, OK, you're an authenticated user.



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Here's a cookie that allows me to track who you are.



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So remember that you're authenticated, but between requests.



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So we call this the request response lifecycle.



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And it's something you need to become familiar with and you'll be doing that as we go through this course.



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But the things to remember are that a Web server is just a part of an application, a Web application.



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You might have a database.



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We will you might have a cache.



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We will not.



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But it's something you may to use later on as you become more familiar with building Web applications.



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We're definitely going to have an application and there might be more than one application on the server



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in this course will be building a monolithic application where all of the code lives in one code base.



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But there's something called the service oriented architecture where your Web application actually consists



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of a series of Web applications.



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So you might build one to authenticate users.



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You might be able build one to generate an invoice, you might build one to generate a Web page, whatever



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it may be.



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But that's beyond the scope of what we're doing in this course.



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But as time goes on and you become more familiar with building Web applications, you'll probably run



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into the service oriented architecture, sometimes called micro services.



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We're not really good at naming things in the world of computer science.



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We kind of use multiple names for the same services, but a service oriented architecture, micro services,



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there are all kinds of things that you might build as time goes on.



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But in this course, we're going to keep it simple.



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We'll build one monolithic application that takes care of generating Web pages and sending them back



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to the user, takes care of the authentication.



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It does everything we need it to do.



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So this is the request response lifecycle.



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And as we go through this course, you'll become intimately familiar with how this works.