我有以下出版商和订阅者：

// publisher.js

var amqp = require('amqplib/callback_api');

amqp.connect('amqp://localhost', function(err, conn) {
  conn.createChannel(function(err, ch) {
    var ex = 'logs';
    var msg = process.argv.slice(2).join(' ') || 'Hello World!';

    ch.assertExchange(ex, 'fanout', {durable: true});
    ch.publish(ex, '', new Buffer(msg));
    console.log(" [x] Sent %s", msg);
  });

  setTimeout(function() { conn.close(); process.exit(0) }, 500);
});

//subscriber.js

var amqp = require('amqplib/callback_api');

amqp.connect('amqp://localhost', function(err, conn) {
  conn.createChannel(function(err, ch) {
    var ex = 'logs';

    ch.assertExchange(ex, 'fanout', {durable: true});

    ch.assertQueue('', {exclusive: true}, function(err, q) {
      console.log(" [*] Waiting for messages in %s. To exit press CTRL+C", q.queue);
      ch.bindQueue(q.queue, ex, '');

      ch.consume(q.queue, function(msg) {
        if(msg.content) {
          console.log(" [x] %s", msg.content.toString());
        }
      }, {noAck: true});
    });
  });
});

如果我运行Advertiser.js发布两条消息，然后运行subscriber.js，我希望订阅者打印我过去发布的两条消息，但实际上订阅者没有收到任何消息。
如何让RabbitMQ持久化已发布的消息，允许任何订阅者从一开始或在他们上次消费的任何地方消费？