Google App Engine is a web application hosting service. By “web application,” we mean an application or service accessed over the Web, usually with a web browser: storefronts with shopping carts, social networking sites, multiplayer games, mobile applications, survey applications, project management, collaboration, publishing, and all the other things we’re discovering are good uses for the Web. App Engine can serve traditional website content too, such as documents and images, but the environment is especially designed for real-time dynamic applications.
In particular, Google App Engine is designed to host applications with many simulta- neous users. When an application can serve many simultaneous users without degrad- ing performance, we say it scales. Applications written for App Engine scale automat- ically. As more people use the application, App Engine allocates more resources for the application and manages the use of those resources. The application itself does not need to know anything about the resources it is using.
Unlike traditional web hosting or self-managed servers, with Google App Engine, you only pay for the resources you use. These resources are measured down to the gigabyte. Billed resources include CPU usage, storage per month, incoming and outgoing band- width, and several resources specific to App Engine services. To help you get started, every developer gets a certain amount of resources for free, enough for small applica- tions with low traffic.
App Engine can be described as three parts: application instances, scalable data storage, and scalable services. In this chapter, we look at each of these parts at a high level. We also discuss features of App Engine for deploying and managing web applications, and for building websites integrated with other Google offerings such as Google Apps, Google Accounts, and Google Cloud Storage.
