Keepalived的VIP单播配置

默认keepalived主机之间利用多播相互通告消息，会造成网络拥塞，可以替换成单播，减少网络流量。

注意：启用 vrrp_strict 时，不能启用单播

#在所有节点vrrp_instance语句块中设置对方主机的IP，建议设置为专用于对应心跳线网络的地址，而非使
用业务网络
unicast_src_ip <IPADDR>  #指定发送单播的源IP
unicast_peer {
   <IPADDR>     #指定接收单播的对方目标主机IP
   ......
}
#启用 vrrp_strict 时，不能启用单播,否则服务无法启动,并在messages文件中记录下面信息
Jun 16 17:50:06 centos8 Keepalived_vrrp[23180]: (m44) Strict mode does not 
support authentication. Ignoring.
Jun 16 17:50:06 centos8 Keepalived_vrrp[23180]: (m44) Unicast peers are not 
supported in strict mode
Jun 16 17:50:06 centos8 Keepalived_vrrp[23180]: Stopped - used 0.000606 user 
time, 0.000000 system time
Jun 16 17:50:06 centos8 Keepalived[23179]: Keepalived_vrrp exited with permanent 
error CONFIG. Terminating
Jun 16 17:50:06 centos8 systemd[1]: keepalived.service: Succeeded.
Jun 16 17