Failed to issue method call: Unit iptables.service failed to load In Centos7

In RHEL 7 / CentOS 7, firewalld was introduced to manage iptables. IMHO, firewalld is more suited for workstations than for server environments.

It is possible to go back to a more classic iptables setup. First, stop and mask the firewalld service:

systemctl stop firewalld
systemctl mask firewalld
Then, install the iptables-services package:

yum install iptables-services
Enable the service at boot-time:

systemctl enable iptables
Managing the service

systemctl [stop|start|restart] iptables
Systemctl doesn't seem to manage the save action like you were able to do in the past with service:

/usr/libexec/iptables/iptables.init save