For RHEL/CentOS/SL etc, you will also need Fedora EPEL repository installed for mongodb, on CentOS it's already available:

(as root or sudo)
# yum install epel-release

Enable the unifi service and the firewall config:

# firewall-cmd --permanent --add-service=unifi 
# firewall-cmd --reload
# systemctl enable unifi.service
# systemctl start unifi.service

Afterwards you should be able to browse to the controller at:

<host>:8443
