If you want to use a deployment tool like Capistrano or Laravel Envoy with symbolic linked release directories, instead of mapping your script to the path of the symlink with $document_root:

location ~ \.php$ {  
    # ...
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    # ...
}

You should instead reference the $realpath_root variable as this allows for all new requests to immediately be mapped to the new release on deployment.

location ~ \.php$ {  
    # ...
    fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;
    fastcgi_param DOCUMENT_ROOT $realpath_root;
    # ...
}