When doing maintenance on a web application, you probably have a custom 503 site, showing your customers that the servers are currently lying on the operating table.
At the dynamic ridesharing service flinc, we touch a certain file on our reverse proxies (e.g. using capistrano deploy:web:disable) when maintenance begins. Nginx then serves a static “we’ve disabled the site for maintenance” site, instead of the actual content.
But wouldn’t it be nice to test your web application before going live for your customers? It sure would. Unfortunately, this is not as simple as a task as you might think, because you cannot nest if directives in an Nginx location and if is evil.