I have OpenStack UI running. I made some changes in the local-setting.py file and restarted the Horizon service using service httpd restart and try to hit OpenStack UI but it returns an error: "HTTP 400 Bad request".
When I revert back all changes, restart the service and try again the error is still there.
Please help me !!
Total agree with above comments, check your apache or httpd log files.
Most probably error cause due to improper info.
added (for centos)  under below file.
/etc/openstack-dashboard/local_settings
ALLOWED_HOSTS = ['XX.XX.XX.XX', 'ControllerName', 'localhost']
Hopefully this will resolve issue.
Unabe to Get OpenStack Login prompt