An App Engine application responds to web requests. It does so by calling request handlers, routines that accept request parameters and return responses. App Engine determines which request handler to use for a given request from the request’s URL, using a configuration file included with the app that maps URLs to handlers.
The application configuration includes metadata about the app, such as its application ID and version number. When you deploy the app to App Engine, all of the app’s files, including the code, configuration files, and static files, are uploaded and associated with the application ID and version number mentioned in the configuration. An app can also have configuration files specific to the services, such as for datastore indexes, task queues, and scheduled tasks. These files are associated with the app in general, not a specific version of the app.
The structure and format of the code and configuration files differ for Python apps and for Java apps, but the concepts are similar. In the next few sections, we will create the files needed for a simple application in both Python and Java, and will look at how to use the tools ...