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RabbitMQ: Delayed Queue

A Delayed Queue in RabbitMQ is a queue where messages are not delivered immediately. They wait for a specified delay before being available to consumers.

RabbitMQ: Delayed Queue

1. Overview

A Delayed Queue in RabbitMQ is a queue where messages are not delivered immediately. They wait for a specified delay before being available to consumers.
Use cases:
  • Sending reminder emails
  • Delayed retries for failed jobs
  • Scheduled notifications

2. Delayed Queue Using DLX (Dead Letter Exchange)

How it Works

  • Messages go into a holding queue first
  • Each message has a TTL (Time-To-Live)
  • After TTL expires, message is dead-lettered to the real queue

Producer Code

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const amqp = require("amqplib");

async function sendDelayedMessage() {
const connection = await amqp.connect("amqp://localhost");
const channel = await connection.createChannel();

// Real queue where message will be consumed
await channel.assertQueue("real_queue", { durable: true });

// Delayed queue (holding queue)
await channel.assertQueue("delayed_queue", {
durable: true,
arguments: {
"x-message-ttl": 5000, // 5 seconds delay
"x-dead-letter-exchange": "", // default exchange
"x-dead-letter-routing-key": "real_queue" // route to real_queue after TTL
}
});

// Send message to delayed queue
channel.sendToQueue("delayed_queue", Buffer.from("Hello after 5 seconds"));

console.log("Message sent to delayed queue. Waiting for delivery...");
setTimeout(() => connection.close(), 1000);
}

sendDelayedMessage();

Consumer Code

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const amqp = require("amqplib");

async function consumeRealQueue() {
const connection = await amqp.connect("amqp://localhost");
const channel = await connection.createChannel();

await channel.assertQueue("real_queue", { durable: true });

console.log("Waiting for messages from real_queue...");
channel.consume("real_queue", (msg) => {
console.log("Received:", msg.content.toString());
channel.ack(msg);
});
}

consumeRealQueue();
Explanation:
  • Message waits in delayed_queue for TTL (5s)
  • Then automatically moved to real_queue
  • Consumer receives it after delay
# message-queue# aws-end-user-messaging# distributed-systems# event-driven# backend
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