Can I have each consumer receive the same messages? Ie, both consumers get message 1, 2, 3, 4, 5, 6? What is this called in AMQP/RabbitMQ speak? How is it normally configured?
No, not if the consumers are on the same queue. From RabbitMQ's AMQP Concepts guide:
it is important to understand that, in AMQP 0-9-1, messages are load balanced between consumers.
This seems to imply that round-robin behavior within a queue is a given, and not configurable. Ie, separate queues are required in order to have the same message ID be handled by multiple consumers.
Is this commonly done? Should I just have the exchange route the message into two separate queues, with a single consumer, instead?
No it's not, single queue/multiple consumers with each each consumer handling the same message ID isn't possible. Having the exchange route the message onto into two separate queues is indeed better.
As I don't require too complex routing, a fanout exchange will handle this nicely. I didn't focus too much on Exchanges earlier as node-amqp has the concept of a 'default exchange' allowing you to publish messages to a connection directly, however most AMQP messages are published to a specific exchange.
Here's my fanout exchange, both sending and receiving:
var amqp = require('amqp');
var connection = amqp.createConnection({ host: "localhost", port: 5672 });
var count = 1;
connection.on('ready', function () {
connection.exchange("my_exchange", options={type:'fanout'}, function(exchange) {
var sendMessage = function(exchange, payload) {
console.log('about to publish')
var encoded_payload = JSON.stringify(payload);
exchange.publish('', encoded_payload, {})
}
// Recieve messages
connection.queue("my_queue_name", function(queue){
console.log('Created queue')
queue.bind(exchange, '');
queue.subscribe(function (message) {
console.log('subscribed to queue')
var encoded_payload = unescape(message.data)
var payload = JSON.parse(encoded_payload)
console.log('Recieved a message:')
console.log(payload)
})
})
setInterval( function() {
var test_message = 'TEST '+count
sendMessage(exchange, test_message)
count += 1;
}, 2000)
})
})
If you don't want to have to ACK each message then you can set the AcknowledgeMode on the SimpleMessageListenerContainer by doing
container.setAcknowledgeMode(AcknowledgeMode.NONE);
take a look at the API reference for more info.
Update: Should be AcknowledgeMode.NONE
Set to AcknowledgeMode.NONE to tell the broker not to expect any acknowledgements, and it will assume all messages are acknowledged as soon as they are sent (this is "autoack" in native Rabbit broker terms). If AcknowledgeMode.NONE then the channel cannot be transactional (so the container will fail on start up if that flag is accidentally set).
Best Answer
An Unacknowledged message implies that it has been read by your consumer, but the consumer has never sent back an ACK to the RabbitMQ broker to say that it has finished processing it.
I'm not overly familiar with the Spring Framework plugin, but somewhere (for your consumer) you will be declaring your queue, it might look something like this (taken from http://www.rabbitmq.com/tutorials/tutorial-two-java.html):
then you will setup your consumer
ackMode above is a boolean, by setting it to false, we're explicitly saying to RabbitMQ that my consumer will acknowledge each message it is given. If this flag was set to true, then you wouldn't be seeing the Unacknowledged count in RabbitMQ, rather as soon as a consumer has read the message off (i.e it has been delivered to the consumer it will remove it from the queue).
To acknowledge a message you would do something like this:
If you can post some of your consumer code then I might be able to help further...but in the mean time take a look at BlockingQueueConsumer specifically: the constructor you will see that you can set the AcknowledgeMode and also take a look at the nextMessage() this will return a Message object which contains a method called getDeliveryTag() this will return a Long which is the ID that you would send back on the basicAck