We recently updated our ECE documentation to address an issue with the firewalld service that we're seeing on CentOS and RHEL. The service is not compatible with Docker and interferes with the installation of ECE. You must disable firewalld with sudo systemctl disable firewalld and reboot before installing or reinstalling ECE.
Also see Limitations and Known Problems and the configuration steps for
Red Hat Enterprise Linux (RHEL) 7 and CentOS 7.
Nik