You need to put your application in "maintenance" mode.
You're performing database updates, or other changes to your application and it'd be best if users couldn't access the system for a while.
php artisan down command.
This sets a flag on your application specifying it's in maintenance mode.
$ php artisan down
Don't forget to handle maintenance mode.
See the Registering a Maintenance Mode Handler recipe.
What this command actually does is creates the empty file
app/storage/meta/down. Existence of this file is the maintenance mode flag.
If your application runs on several machines in a web farm then you must use the
php artisan down command on each machine.