Cloud to the Developer

Cloud computing is a fundamental change from how computers and software have worked in the past. Traditionally, if you wanted to run an application, you went out and bought a computer and software, set it up on your own premises, and ran your program. You needed to pick out which operating system you were going to run, handle the installation of your software, and maintain your computer—keeping track of software upgrades, security, backups, and so on.

With cloud computing, you don’t do any of that. If you’re a user of the cloud, you buy access to the application you want and then connect to it from anywhere. Installing the software, maintaining the hardware and software where the application runs, making sure that the data is kept safe and secure—none of that is your concern. In the cloud, you buy software as a service. If you need more storage than a typical user, you buy extra storage from the service provider. If that means buying and installing a new disk drive, that’s up to the provider. You just buy storage-as-a-service from them: how they provide it is their problem. You tell them what you need—in both the physical sense (“I need 1TB of storage.”) and in less tangible quality-of-service senses (“I need to guarantee that my storage is transactional, so that after I commit a change, data will never be lost.”). You tell them your requirements, and some cloud provider will sell you a service that meets those requirements.

What this means is that when you’re developing for the cloud, instead of buying a computer and running software on it, you break things down to basic building blocks, buy those pieces from service providers, and put them together however you want to build a system.

The building blocks are the resources you need to run a program or to perform a task. Resources include things like processing time, network bandwidth, disk storage, and memory. As a user of the cloud, you don’t need to be concerned about where these resources are located. You know what you need, and you buy that from whoever can provide it to you most conveniently.

For developers, cloud computing introduces an even bigger change. When you develop for the cloud, you’re not building a piece of software to sell to your customers—you’re building a service for your customers to use. Understanding that difference is crucial: you need to design your application around the idea that it’s a service you’re going to provide to users, not a standalone application that they’re going to install on their computers. Your customers are going to choose a service based on the tasks they want to accomplish, so your application needs to be designed with the task in mind, and you must provide it in the most flexible way possible.

For example, if you want to build a to-do list application for a desktop computer, it’s a fairly straightforward process. There are lots of variations in how you can arrange the UI, but the basic idea of what you’re building is obvious. You would build one UI—after all, why would you need more than one? And you’d build it mainly for a single user. If you are developing this to-do list application for the cloud, though, you’d want multiple UIs: at the very least, you’d want one UI for people accessing your service using their desktop computer and one for people using a mobile browser on a cell phone. You’ d probably want to provide an open interface that other people could use for building clients for other devices. And you’d need to design it for multiple users; if you put an application in the cloud, there’s only one program, but it can be used by lots of people. So you need to design it around the assumption that even if users never work together using your application, it’s still a multi-user system.

For developers, the most exciting aspect of cloud computing is its scalability. When you’re developing in the cloud, you can write a simple program to be used by one or two people—and then, without ever changing a line of code, that program can scale up to support millions of users. The program is scale-neutral: you write it so it will work equally well for one dozen users or one million users. As you get more users, all you need to do is buy more resources—and your program will just work. You can start with a simple program running on one server somewhere in the cloud and scale up by adding resources until you’ve got millions of users.

Source of Information : Pragmatic - Code in the Cloud Programming Google App Engine 2011