Modify /etc/citrusleaf/citrusleaf.conf as my example.
After modifying just start new node, it will be added an existing cluster automatically. You can confirm it on /var/log/citrusleaf.log with the following message.
I changed ip address to 172.28.206.73 - it's wrong address -, after I got succeeded with above configuration. So I fixed it to 172.28.206.72 and restarted node. But I got some non normal message.
I issued the command and failed to get expected result - ClusterSize 2 -.
I fixed this event by restarting all nodes.