Summary - Message queue

Combine producer, consumer and retry to write a background job system.

Summary - Message queue

In this group you learned to set up a message queue with Bull: creating a queue with new Bull("name"), writing a producer with queue.add, defining a consumer with queue.process, and setting retries with attempts/backoff.

Now you will combine these into a small email queue skeleton. The skeleton will create a queue, add a message, and define a consumer. This mini task shows how the queue tools combine.

Email queue design

The skeleton of an email queue is this: a queue with new Bull("email"), a message with queue.add, a consumer with queue.process. Retry and backoff are also added.

Flow: const kuyruk = new Bull("email"); kuyruk.add({ to: "alex@x.com" }, { attempts: 3, backoff: 1000 }); kuyruk.process(async (job) => { console.log("Sent: " + job.data.to); });. The message is added to the queue; the consumer takes it and sends the email. On failure it is retried 3 times. On top of this skeleton you can add priority, scheduling and a dead-letter queue (DLQ). Bull manages all of this with a simple API.

Exercise Build the email queue skeleton

Import bull and create kuyruk = new Bull("email"). Define a consumer with kuyruk.process(async (job) => { console.log("Sent: " + job.data.to); }). Print "Queue system ready" with console.log.

Show example solution

const Bull = require("bull");
const kuyruk = new Bull("email");
kuyruk.process(async (job) => {
  console.log("Sent: " + job.data.to);
});
console.log("Queue system ready");

Test yourself

What pieces does the queue skeleton combine?
```
new Bull + add + process
```
- Only require
- Only console.log
- Only attempts
- Bull, add, process and backoff
Show answer

Bull, add, process and backoff — Bull + add + process + backoff combine.
Match each tool to its role

new Bull

Creates a queue
queue.add

Adds a message
queue.process

Defines a consumer
backoff

Waits between retries

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