[peter@minion ~]$ docker swarm join --token SWMTKN-1-3mj5po3c7o04le7quhkdhz6pm9b8ziv3qe0u7hx0hrgxsnaram-0p1f40vtehanu6ugw8ug2wasy 10.0.0.10:2377
Error response from daemon: error while validating Root CA Certificate: x509: certificate has expired or is not yet valid
原理：docker swarm node之间是加密传输，docker swarm init时会创建CA证书。这里提示证书过期，可能是主机当前时间不对。
解决：sudo ntpdate time.nist.gov 同步一下时间