es版本6.7，3个节点，已生成各自证书，配置如下
xpack.security.enabled: true
xpack.security.transport.ssl.enabled: true
xpack.security.transport.ssl.verification_mode: certificate
xpack.security.transport.ssl.keystore.path: elastic-certificates.p12
xpack.security.transport.ssl.truststore.path: elastic-certificates.p12
加入不了集群，其他2个节点报错
[2019-06-03T16:24:49,961][WARN ][o.e.t.OutboundHandler ] [prd_mdi_node2] send message failed [channel: Netty4TcpChannel{localAddress=/10.129.168.22:9301, remoteAddress=/10.129.192.22:42448}]
java.nio.channels.ClosedChannelException: null
at io.netty.channel.AbstractChannel$AbstractUnsafe.write(...)(Unknown Source) ~[?:?]
