在安装过程中只配置了cluster.initial_master_nodes 属性，没有配置discovery.seed_hosts
启动的时候遇到如下俩个错误：
[1]: memory locking requested for elasticsearch process but memory is not locked
[2]: max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]
解决办法：
1.在 /etc/security/limits.conf加入一下配置：
es hard memlock unlimited
es soft memlock unlimited
其中es为我启动的es的用户，这个根据实际情况修改
2.运行此命令修改vm限制：sysctl -w vm.max_map_count=262144
启动无误后，看日志出现以下警告：
master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster, and this node must discover master-eligible node
意思就是找不到master节点，每个节点以local模式启动，此问题找了半天，最后发现是因为没有在discovery.seed_hosts中配置master nodes的hosts.