Programming Google App Engine with Java

Chapter 3. Configuring an Application

Many of App Engine’s features can be tailored and controlled using configuration files that you deploy alongside your code. A few of these features apply to the entire project’s use of a service, such as datastore index configuration (which we’ll cover in Chapter 7). The most important set of configuration controls how App Engine manages incoming requests, how App Engine runs your code on its scalable servers, and how App Engine routes requests to your code on those servers.

To build an App Engine application, you write code for one or more request handlers, and provide configuration describing to App Engine which requests go to which handlers. The life of a request handler begins when a single request arrives, and ends when the handler has done the necessary work and computed the response. App Engine does all the heavy lifting of accepting incoming TCP/IP connections, reading HTTP request data, ensuring that an instance of your app is running on an application server, routing the request to an available instance, calling the appropriate request handler code in your app, and collecting the response from the handler and sending it back over the connection to the client.

The system that manages and routes requests is known generally as the App Engine frontend. You can configure the frontend to handle different requests in different ways. For instance, you can tell the frontend to route requests for some URLs to App Engine’s static file servers ...