Delay message rabbitmq on nodejs

Question

I'm trying to add some functionality for rabbitmq with delay messages. Actually I need to get this message after 2 weeks. As I know we do not need any plugin. Also when this message invokes, how should I reschedule new x delay exchanger to invoke again over 2 weeks. Where shoul I added this x delay message.

config

"messageQueue": {
        "connectionString": "amqp://guest:guest@localhost:5672?heartbeat=5",
        "queueName": "history",
        "exchange": {
            "type": "headers",
            "prefix": "history."
        },
        "reconnectTimeout": 5000
    },

service:

import amqplib from 'amqplib'
import config from 'config'

import logger from './logger'

const {reconnectTimeout, connectionString, exchange: {prefix, type: exchangeType}, queueName} = config.messageQueue

const onConsume = (expectedMessages, channel, onMessage) => async message => {
    const {fields: {exchange}, properties: {correlationId, replyTo}, content} = message

    logger.silly(`consumed message from ${exchange}`)

    const messageTypeName = exchange.substring(exchange.startsWith(prefix) ? prefix.length : 0)

    const messageType = expectedMessages[messageTypeName]

    if (!messageType) {
        logger.warn(`Unexpected message of type ${messageTypeName} received. The service only accepts messages of types `, Object.keys(expectedMessages))

        return
    }

    const deserializedMessage = messageType.decode(content)

    const object = deserializedMessage.toJSON()

    const result = await onMessage(messageTypeName, object)

    if (correlationId && replyTo) {
        const {type, response} = result

        const encoded = type.encode(response).finish()

        channel.publish('', replyTo, encoded, {correlationId})
    }
}

const startService = async (expectedMessages, onMessage) => {

    const restoreOnFailure = e => {
        logger.warn('connection with message bus lost due to error', e)
        logger.info(`reconnecting in ${reconnectTimeout} milliseconds`)

        setTimeout(() => startService(expectedMessages, onMessage), reconnectTimeout)
    }

    const exchanges = Object.keys(expectedMessages).map(m => `${prefix}${m}`)

    try {
        const connection = await amqplib.connect(connectionString)

        connection.on('error', restoreOnFailure)

        const channel = await connection.createChannel()

        const handleConsume = onConsume(expectedMessages, channel, onMessage)

        const queue = await channel.assertQueue(queueName)

        exchanges.forEach(exchange => {
            channel.assertExchange(exchange, exchangeType, {durable: true})

            channel.bindQueue(queue.queue, exchange, '')
        })

        logger.debug(`start listening messages from ${exchanges.join(', ')}`)

        channel.consume(queue.queue, handleConsume, {noAck: true})
    }
    catch (e) {
        logger.warn('error while subscribing for messages message', e)

        restoreOnFailure(e)
    }
}

export default startService

You can use a scheduler to schedule sending message after 2 weeks by using node-schedule — TGW
– TGW, Commented Apr 2, 2018 at 12:42

theMayer · Accepted Answer · 2018-04-03 20:36:36Z

RabbitMQ has a plug-in for scheduling messages. You can use it, subject to an important design caveat which I explain below.

Use Steps

You must first install it:

rabbitmq-plugins enable rabbitmq_delayed_message_exchange

Then, you have to set up a delayed exchange:

Map<String, Object> args = new HashMap<String, Object>();
args.put("x-delayed-type", "direct");
channel.exchangeDeclare("my-exchange", "x-delayed-message", true, false, args);

Finally, you can set the x-delay parameter (where delay is in milliseconds).

byte[] messageBodyBytes = "delayed payload".getBytes();
AMQP.BasicProperties.Builder props = new AMQP.BasicProperties.Builder();
headers = new HashMap<String, Object>();
headers.put("x-delay", 5000);
props.headers(headers);
channel.basicPublish("my-exchange", "", props.build(), messageBodyBytes);

Two weeks is equal to (7*24*60*60*1000 = 604,800,000) milliseconds.

Important Caveat As I explained in this answer, this is a really bad thing to ask the message broker to do.

It's important to keep in mind, when dealing with message queues, they perform a very specific function in a system: to hold messages while the processor(s) are busy processing earlier messages. It is expected that a properly-functioning message queue will deliver messages as soon as reasonable. Basically, the fundamental expectation is that as soon as a message reaches the head of the queue, the next pull on the queue will yield the message -- no delay.

Delay becomes a result of how a system with a queue processes messages. In fact, Little's Law offers some interesting insights into this. If you're going to stick an arbitrary delay in there, you really have no need of a message queue to begin with - all your work is scheduled up front.

So, in a system where a delay is necessary (for example, to join/wait for a parallel operation to complete), you should be looking at other methods. Typically a queryable database would make sense in this particular instance. If you find yourself keeping messages in a queue for a pre-set period of time, you're actually using the message queue as a database - a function it was not designed to provide. Not only is this risky, but it also has a high likelihood of hurting the performance of your message broker.

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