如何确保邮件平均发送给所有消费者

Question

In our company, we built a push service in Go and we put it on four machines to make sure transmission speed, when we need send notifications we send message to rabbitMQ, then push service will get the messages from queue, but sometimes we find there is only one machines get the message.

Here is the config of rabbitMQ consumers:

msgs, err := ch.Consume(
    q.Name,      // queue
    consumerTag, // consumer
    true,        // auto-ack
    false,       // exclusive
    false,       // no-local
    false,       // no-wait
    nil,         // args
)

How should I set the config to make sure each consumer get the same quantity of messages?

Answer 1

RabbitMQ just sends the messages to the subscribers without checking the unacknowledged messages. To get the fair and Round-Robin distribution you can do the following

• First set the QOS in the consumer channel

      err = ch.Qos(
          1,     // prefetch count
          0,     // prefetch size
          false, // global
  )
  

• Next set the auto acknowledge to false in the consumer

      msgs, err := ch.Consume(
          q.Name, // queue
          "",     // consumer
          false,  // auto-ack
          false,  // exclusive
          false,  // no-local
          false,  // no-wait
          nil,    // args
  )
  

• Next send the ack to the Rabbitmq at the end of processing the message each time from each consumer

  msg.Ack(false)

This pattern is called work queue, this avoid the loss of the messages also, if the consumer goes down before sending the ack then those messages will be re-queued and delivered to another consumer for processing. For more info on this you can check out this link