这里我可以直接连接兔子节点：

(app@centos7-mq)1> net_kernel:connect_node('rabbit@centos7-mq').
true
(app@centos7-mq)2> nodes().
['rabbit@centos7-mq']

但使用程序时显示错误。

Erlang RabbitMQ Client library

RabbitParams=#amqp_params_direct{username=?RABBIT_USERNAME,
                      password=?RABBIT_PASSWORD, virtual_host=?VHOST, node='rabbit@centos7-mq'},
    Connection = amqp_connection:start(RabbitParams),
    io:format("amqp_connection:start result: ~p~n", [Connection]).

错误内容如下：

amqp_connection:start result: {error,{nodedown,'rabbit@centos7-mq'}}

那么，它有什么问题吗？
=============这是示例

-module(amqp_direct).
-include_lib("amqp_client/include/amqp_client.hrl").
-compile([export_all]).
-compile(nowarn_export_all).
-define(RABBIT_USERNAME, <<"your user">>).
-define(RABBIT_PASSWORD, <<"your password">>).
-define(VHOST, <<"your vhost">>).
-define(NODE, 'your server node').

connect_amqp() ->
    RabbitParams=#amqp_params_direct{username=?RABBIT_USERNAME,
                      password=?RABBIT_PASSWORD, virtual_host=?VHOST, node=?NODE},
    io:format("amqp_connection:start begin ~n"),
    Connection = amqp_connection:start(RabbitParams),
    io:format("amqp_connection:start result: ~p~n", [Connection]),
    Connection.

start() ->
   Connection=amqp_example:connect_amqp(),
   "Finish".