join 格式：
kubeadm join 192.168.99.11:6443 --token 4qcl2f.gtl3h8e5kjltuo0r \
--discovery-token-ca-cert-hash sha256:7ed5404175cc0bf18dbfe53f19d4a35b1e3d40c19b10924275868ebf2a3bbe6e
get关键的几部分： ip、token、cert sha256
token：
[root@master ~]# kubeadm token list
TOKEN TTL EXPIRES USAGES DESCRIPTION EXTRA GROUPS
xh7hwq.a62kp9myjdde3nif 22h 2020-06-05T15:54:14+08:00 authentication,signing <none> system:bootstrappers:kubeadm:default-node-token
cert sha256:
openssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex | sed 's/^.* //'
ebef143fad8ffd9dd9d320bb9ee5fc5ac275c88095140e039dea1e0a5f9638a8
