If you're using PHP with fpm (common in this day and age), be aware that __DIR__ and __FILE__ will return values based on the fpm root which MAY differ from its actual location on the file system.
This can cause temporary head-scratching if deploying an app where php files within the web root pull in PHP files from outside of itself (a very common case). You may be wondering why __DIR__ returns "/" when the file itself lives in /var/www/html or whathaveyou.
You might handle such a situation by having NGINX explicitly add the necessary part of the path in its fastcgi request and then you can set the root on the FPM process / server / container to be something other than the webroot (so long as no other way it could become publicly accessible).
Hope that saves someone five minutes who's moving code to FPM that uses __DIR__.
