ALLOWED_HOSTS and Django
Also, if you have a service like gunicorn between your localhost and your nginx server or apache2 server. Remember to restart it too.
sudo systemctl restart gunicorn
I tried to launch a Django 1.11 project on production server. When I start the app I see the following error:

Invalid HTTP_HOST header: 'bla-bla-bla.bla-bla-vla.com'. You may need to add u'bla-bla-bla.bla-bla-vla.com' to ALLOWED_HOSTS**

But, host "bla-bla-bla.bla-bla-vla.com" has been added to ALLOWED_HOSTS in settings.py already! 
I tried to switch DEBUG from False to True and back. It works fine, then.
What am I doing wrong?