I need to add maintenance page to some rails app, running with passenger and nginx. Here’s some config and steps.

You just need to add static html file to app_root/public/maintenance.html – and I assume css files on /assets url.

so, here’s nginx config:

server {
  listen 80;
  server_name = www.example.com;
  root /home/deploy/www.example.com/public;
  passenger_enabled on;
  passenger_min_instances 5;

  set $maintenance 0;

  # is there maintenance file set?
  if (-f $document_root/../tmp/maintenance.txt) {
    set $maintenance 1;
  }

  # exclude /assets
  if ( $uri ~* ^/assets\/\.* ) {
    set $maintenance 0;
  }

  # in maintenance mode - send 503 status
  if ($maintenance = 1) {
    return 503;
  }

  # maintenance mode
  error_page 503 @503;

  # rewrite everything to maintenance.html
  location @503 {
    rewrite ^ /maintenance.html last;
    break;
  }
}

setting maintance mode is really simple – set app_root/tmp/maintenance.txt file – when escaping, just remove that file.