USAGE

    $ mhaws [subcommand] --interface_id=ENI-id [... args passed by MHA]

    required arguments:
      1. failover method is ENI attach/detach
        --interface_id=[ENI-id for master VIP]
      
      2. failover method is RouteTable change destination
        --route_table_id=[RouteTable-id]
        --vip=[master VIP]

    subcommand:
      master_ip_failover
      master_ip_online_change
      shutdown