The file module is built into AWS, and is used to send a single file in response to all requests with a given prefix. It has one argument, which should be the name of a text file that can be returned to the client. If this is not the case, a server configuration error is indicated. For instance, to send all requests for /adult-stuff a note pointing out that the contents have been rendered illegal in this country, you would use the single file map:
map / file notes:no-longer-legal.html