[MUSIC] So how do we talk to 150,000 servers in Amazon EC2? How does a lonely little mobile device, that's connected to some network, out in the wild. Get access to these thousands of servers, that are sitting in some cloud computing environment. So how do we get from there to there? Well the way that we're going to talk about getting from the mobile device to the cloud is through the use of HTTP. And what you can think of HTTP is, it's basically a dialog or a language that a mobile device can use to speak to a cloud, it's a protocol, an application protocol, for communicating between devices on a network. Now. We're going to use HTTP here as our protocol for communication. But it's helpful to have a little bit of history. And understand what HTTP, was originally built for. HTTP is the protocol, or the way that your browser communicates with a web server. In order to retrieve resources from that web server such as a web page. So when you go and you log in to Facebook, for example, your browser is sending HTTP, probably a series of HTTP requests, to one or more Facebook servers. And then that server, or servers that are receiving the request or requests. Send data back to your browser. HTTP is a client-server protocol and what that means is that, the interactions that are mediated via the HTTP protocol, are always initiated by a client that wants to. Access or request, some resource on the server. So the server has a series of resources, that it can provide to the client, and the client sends requests for those resources and the server. Returns responses to those requests. And the responses may have the resource that was requested or it may have a message indicating why the Server could or couldn't process the request, that the client sent. But fundamentally, the HTTP protocol is an application protocol that is client-server. So, the client will always be initiating the communications. And there are some changes to this with newer things like web sockets, that we'll talk about later in this course. But in general, the client will always start the interaction. And the server will receive the interactions. And process them. So, this is the fundamental way, that HTTP works. Now the client can be either a mobile device as we'll focus on in this class, or it can be a browser. So, we can have a mobile device be the client, or we can have a browser be the client. Or we could have some other device, maybe in the internet of things, we use HTTP as the protocol to communicate between different pieces of equipment in a factory and the different controllers, that are monitoring their status. So HTTP is a general purpose protocol. That can be used, to communicate between a client and a server. Now one of the reasons that HTTP has become so popular for mobile integration with cloud, is that HTTP is a widely used protocol already. All of the websites that you visit are already using. HTTP as the protocol that's being used to access those web res, resources. So there's already so much infrastructure that's been built up and so much investment that has been put into HTTP protocol, and so much understanding of how the HTTP protocol works, that organizations naturally want to reuse. That infrastructure and investment, on their mobile platforms. So by using HTTP, they can write a server side, that provides access to these resources, which could be a service, or could be a web page. And, they can provide a common interface to those resources, through HTTP. It's a common protocol and a common server site interface, to access those resources. So when a server sends a response back, it doesn't necessarily have to care whether the person or thing that's consuming that response is a mobile device or a browser, or some other thing that it's never seen before. As long as that thing knows how to speak the HTTP protocol, it can consume the resources and services, that are available on that server.
