I am just starting to use RabbitMQ and AMQP in general.
Most of the RabbitMQ documentation seems to be focused on round-robin, ie where a single message is consumed by a single consumer, with the load being spread between each consumer. This is indeed the behavior I witness.
An example: the producer has a single queue, and send messages every 2 sec:
var amqp = require('amqp');
var connection = amqp.createConnection({ host: "localhost", port: 5672 });
var count = 1;
connection.on('ready', function () {
var sendMessage = function(connection, queue_name, payload) {
var encoded_payload = JSON.stringify(payload);
connection.publish(queue_name, encoded_payload);
}
setInterval( function() {
var test_message = 'TEST '+count
sendMessage(connection, "my_queue_name", test_message)
count += 1;
}, 2000)
})
And here's a consumer:
var amqp = require('amqp');
var connection = amqp.createConnection({ host: "localhost", port: 5672 });
connection.on('ready', function () {
connection.queue("my_queue_name", function(queue){
queue.bind('#');
queue.subscribe(function (message) {
var encoded_payload = unescape(message.data)
var payload = JSON.parse(encoded_payload)
console.log('Recieved a message:')
console.log(payload)
})
})
})
If I start the consumer twice, I can see that each consumer is consuming alternate messages in round-robin behavior. Eg, I'll see messages 1, 3, 5 in one terminal, 2, 4, 6 in the other.
My question is:
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?
Is this commonly done? Should I just have the exchange route the message into two separate queues, with a single consumer, instead?
If you happen to be using the amqplib library as I am, they have a handy example of an implementation of the Publish/Subscribe RabbitMQ tutorial which you might find handy.
Yes each consumer can receive the same messages. have a look at http://www.rabbitmq.com/tutorials/tutorial-three-python.html http://www.rabbitmq.com/tutorials/tutorial-four-python.html http://www.rabbitmq.com/tutorials/tutorial-five-python.html
for different ways to route messages. I know they are for python and java but its good to understand the principles, decide what you are doing and then find how to do it in JS. Its sounds like you want to do a simple fanout (tutorial 3), which sends the messages to all queues connected to the exchange.
The difference with what you are doing and what you want to do is basically that you are going to set up and exchange or type fanout. Fanout excahnges send all messages to all connected queues. Each queue will have a consumer that will have access to all the messages separately.
Yes this is commonly done, it is one of the features of AMPQ.
Fan out was clearly what you wanted. fanout
read rabbitMQ tutorial: https://www.rabbitmq.com/tutorials/tutorial-three-javascript.html
here's my example:
Publisher.js:
amqp.connect('amqp://<user>:<pass>@<host>:<port>', async (error0, connection) => {
if (error0) {
throw error0;
}
console.log('RabbitMQ connected')
try {
// Create exchange for queues
channel = await connection.createChannel()
await channel.assertExchange(process.env.EXCHANGE_NAME, 'fanout', { durable: false });
await channel.publish(process.env.EXCHANGE_NAME, '', Buffer.from('msg'))
} catch(error) {
console.error(error)
}
})
Subscriber.js:
amqp.connect('amqp://<user>:<pass>@<host>:<port>', async (error0, connection) => {
if (error0) {
throw error0;
}
console.log('RabbitMQ connected')
try {
// Create/Bind a consumer queue for an exchange broker
channel = await connection.createChannel()
await channel.assertExchange(process.env.EXCHANGE_NAME, 'fanout', { durable: false });
const queue = await channel.assertQueue('', {exclusive: true})
channel.bindQueue(queue.queue, process.env.EXCHANGE_NAME, '')
console.log(" [*] Waiting for messages in %s. To exit press CTRL+C");
channel.consume('', consumeMessage, {noAck: true});
} catch(error) {
console.error(error)
}
});
here is an example i found in the internet. maybe can also help. https://www.codota.com/code/javascript/functions/amqplib/Channel/assertExchange
There is one interesting option in this scenario I haven`t found in answers here.
You can Nack messages with "requeue" feature in one consumer to process them in another. Generally speaking it is not a right way, but maybe it will be good enough for someone.
https://www.rabbitmq.com/nack.html
And beware of loops (when all concumers nack+requeue message)!
RabbitMQ / AMQP: single queue, multiple consumers for same message and page refresh.
rabbit.on('ready', function () { });
sockjs_chat.on('connection', function (conn) {
conn.on('data', function (message) {
try {
var obj = JSON.parse(message.replace(/\r/g, '').replace(/\n/g, ''));
if (obj.header == "register") {
// Connect to RabbitMQ
try {
conn.exchange = rabbit.exchange(exchange, { type: 'topic',
autoDelete: false,
durable: false,
exclusive: false,
confirm: true
});
conn.q = rabbit.queue('my-queue-'+obj.agentID, {
durable: false,
autoDelete: false,
exclusive: false
}, function () {
conn.channel = 'my-queue-'+obj.agentID;
conn.q.bind(conn.exchange, conn.channel);
conn.q.subscribe(function (message) {
console.log("[MSG] ---> " + JSON.stringify(message));
conn.write(JSON.stringify(message) + "\n");
}).addCallback(function(ok) {
ctag[conn.channel] = ok.consumerTag; });
});
} catch (err) {
console.log("Could not create connection to RabbitMQ. \nStack trace -->" + err.stack);
}
} else if (obj.header == "typing") {
var reply = {
type: 'chatMsg',
msg: utils.escp(obj.msga),
visitorNick: obj.channel,
customField1: '',
time: utils.getDateTime(),
channel: obj.channel
};
conn.exchange.publish('my-queue-'+obj.agentID, reply);
}
} catch (err) {
console.log("ERROR ----> " + err.stack);
}
});
// When the visitor closes or reloads a page we need to unbind from RabbitMQ?
conn.on('close', function () {
try {
// Close the socket
conn.close();
// Close RabbitMQ
conn.q.unsubscribe(ctag[conn.channel]);
} catch (er) {
console.log(":::::::: EXCEPTION SOCKJS (ON-CLOSE) ::::::::>>>>>>> " + er.stack);
}
});
});
As I assess your case is:
I have a queue of messages (your source for receiving messages, lets name it q111)
I have multiple consumers, which I would like to do different things with the same message.
Your problem here is while 3 messages are received by this queue, message 1 is consumed by a consumer A, other consumers B and C consumes message 2 and 3. Where as you are in need of a setup where rabbitmq passes on the same copies of all these three messages(1,2,3) to all three connected consumers (A,B,C) simultaneously.
While many configurations can be made to achieve this, a simple way is to use the following two step concept:
Note: While using this concept don't consume directly from the source queue(q111), as messages already consumed wont be shovelled to your Fanout exchange.
If you think this does not satisfies your exact requirement... feel free to post your suggestions :-)
The send pattern is a one-to-one relationship. If you want to "send" to more than one receiver you should be using the pub/sub pattern. See http://www.rabbitmq.com/tutorials/tutorial-three-python.html for more details.
To get the behavior you want, simply have each consumer consume from its own queue. You'll have to use a non-direct exchange type (topic, header, fanout) in order to get the message to all of the queues at once.
The last couple of answers are almost correct - I have tons of apps that generate messages that need to end up with different consumers so the process is very simple.
If you want multiple consumers to the same message, do the following procedure.
Create multiple queues, one for each app that is to receive the message, in each queue properties, "bind" a routing tag with the amq.direct exchange. Change you publishing app to send to amq.direct and use the routing-tag (not a queue). AMQP will then copy the message into each queue with the same binding. Works like a charm :)
Example: Lets say I have a JSON string I generate, I publish it to the "amq.direct" exchange using the routing tag "new-sales-order", I have a queue for my order_printer app that prints order, I have a queue for my billing system that will send a copy of the order and invoice the client and I have a web archive system where I archive orders for historic/compliance reasons and I have a client web interface where orders are tracked as other info comes in about an order.
So my queues are: order_printer, order_billing, order_archive and order_tracking All have the binding tag "new-sales-order" bound to them, all 4 will get the JSON data.
This is an ideal way to send data without the publishing app knowing or caring about the receiving apps.
Just read the rabbitmq tutorial. You publish message to exchange, not to queue; it is then routed to appropriate queues. In your case, you should bind separate queue for each consumer. That way, they can consume messages completely independently.
I think you should check sending your messages using the fan-out exchanger. That way you willl receiving the same message for differents consumers, under the table RabbitMQ is creating differents queues for each one of this new consumers/subscribers.
This is the link for see the tutorial example in javascript https://www.rabbitmq.com/tutorials/tutorial-one-javascript.html
Source: Stackoverflow.com