Associate a external IP

def associate_public_ip(self, instance_id, public_ip_id, private_ip=None):
        """Associate a external IP"""
        floating_ip = self.client.floating_ips.get(public_ip_id)
        floating_ip = floating_ip.to_dict()
        address = floating_ip.get('ip')

        self.client.servers.add_floating_ip(instance_id, address, private_ip)

        return True