1.2. How Do You Build Web Applications?

To build a web application, we need to create at least two major components: a hardware platform and software platform. Forsmall, simple applications, a hardware platform may comprise a single shared server running a web server and a database. Atsmall scales we don't need to think about hardware as a component of our applications, but as we start to scale out, it becomes a more and more important part of the overall design. In this book we'll look extensively at both sides of applicationdesign and engineering, how they affect each other, and how we can tie the two together to create an effective architecture.

Developers who have worked at the small scale might be asking themselves why we need to bother with "platform design" when we could just use some kind of out-of-the-box solution. For small-scale applications, this can be a great idea. We save time and money up front and get a working and serviceable application. The problem comes at larger scalesthere are no off-the-shelf kits that will allow you to build something like Amazon or Friendster. While building similar functionality might be fairly trivial, making that functionality work for millions of products, millions of users, and without spending fartoo much on hardware requires us to build something highly customized and optimized for our exact needs. There's a good reason why the largest applications on the Internet are all bespoke creations: no other approach can create massively scalableapplications within a reasonable budget.

We've already said that at the core of web applications we have some set of data that can be accessed and perhaps modified. Within the software element of an application, we need to decide how we store that data (a schema), how we access and modify it (business logic), and how we present it to our users (interaction logic). In Chapter 2 we'll be looking at these different components, how they interact, and what comprises them. A good application design works down from the very top, defining software and hardware architecture, the components that comprise your platform, and the functionality implemented by those layers.

This book aims to be a practical guide to designing and building large-scale applications. By the end of the book, you'll have a good idea of how to go about designing an application and its architecture, how to scale your systems, and how to go about implementing and executing those designs.