The latest Django update, version 1.10.3 adds an important change to how Django handles the ALLOWED_HOSTS setting in your project.
Previously, when running in debug mode (with DEBUG=True setting) Django ignored the ALLOWED_HOSTS setting, accepting any hostname. Since the latest update Django will validate the values in this setting regardless of the DEBUG setting.
For convenience, if ALLOWED_HOSTS is empty and DEBUG=True, the following variations of localhost are allowed [‘localhost’, ‘127.0.0.1’, ‘::1’].
This change might present an issue for you if you are running a QA version of your project with the DEBUG setting or if you’re developing using production settings in the ALLOWED_HOSTS setting.