rabbitmq使用dead letter机制来进行retry

首先建立 工作exchange和工作queue，指定工作队列的x-dead-letter-exchange到重试exchenge

var workQueueArgs = new Dictionary<string, object> {
    { "x-dead-letter-exchange", RETRY_EXCHANGE },
};

channel.ExchangeDeclare(WORK_EXCHANGE, "direct");
channel.QueueDeclare(WORK_QUEUE, true, false, false, workQueueArgs);
channel.QueueBind(WORK_QUEUE, WORK_EXCHANGE, "", null);

之后建立重试exchange和重试queue

var queueArgs = new Dictionary<string, object> {
    { "x-dead-letter-exchange", WORK_EXCHANGE },
    { "x-message-ttl", RETRY_DELAY }
};

channel.ExchangeDeclare(RETRY_EXCHANGE, "direct");
channel.QueueDeclare(RETRY_QUEUE, true, false, false, queueArgs);
channel.QueueBind(RETRY_QUEUE, RETRY_EXCHANGE, "", null);

重试队列需要2个属性，一个是 x-dead-letter-exchange，指向到工作exchange

一个是过期时间（这里等于是多少秒后重试）

监听工作队列，处理消息

QueueingBasicConsumer consumer = new QueueingBasicConsumer(channel);
channel.BasicConsume(WORK_QUEUE, false, consumer);

while (true)
{
    BasicDeliverEventArgs e = (BasicDeliverEventArgs)consumer.Queue.Dequeue();
    var message = Encoding.UTF8.GetString(e.Body);
    try
    {
        //throw new Exception("");
        channel.BasicAck(e.DeliveryTag, false);
    }
    catch
    {
        channel.BasicNack(e.DeliveryTag, false, false);
    }
}

处理成功调用ack，处理不成功调用nack，

调用nack后，会根据工作队列的x-dead-letter-exchange自动把消息发到重试队列

重试队列等几秒（x-message-ttl）后，就认为是自动失败了，又会根据重试队列的x-dead-letter-exchange发送回工作队列