typescript 50 lines · 7 steps

Processing background email jobs in NestJS

A BullMQ worker consumes queued email jobs, dispatches them by name, and reports progress and failures.

Explained by highlit
NestJS Intermediate job-queue background-processing dependency-injection event-handling
1import { Processor, WorkerHost, OnWorkerEvent } from '@nestjs/bullmq';
2import { Logger } from '@nestjs/common';
3import { Job } from 'bullmq';
4import { MailerService } from '../mailer/mailer.service';
5import { UsersService } from '../users/users.service';
6 
7interface WelcomeEmailData {
8 userId: string;
9 locale: string;
10}
11 
12@Processor('emails', { concurrency: 5 })
13export class EmailsProcessor extends WorkerHost {
14 private readonly logger = new Logger(EmailsProcessor.name);
15 
16 constructor(
17 private readonly mailer: MailerService,
18 private readonly users: UsersService,
19 ) {
20 super();
21 }
22 
23 async process(job: Job): Promise<void> {
24 switch (job.name) {
25 case 'welcome':
26 return this.handleWelcome(job as Job<WelcomeEmailData>);
27 default:
28 throw new Error(`Unhandled email job: ${job.name}`);
29 }
30 }
31 
32 private async handleWelcome(job: Job<WelcomeEmailData>): Promise<void> {
33 const { userId, locale } = job.data;
34 const user = await this.users.findByIdOrFail(userId);
35 
36 await job.updateProgress(50);
37 await this.mailer.send({
38 to: user.email,
39 template: 'welcome',
40 locale,
41 context: { name: user.firstName },
42 });
43 await job.updateProgress(100);
44 }
45 
46 @OnWorkerEvent('failed')
47 onFailed(job: Job, err: Error): void {
48 this.logger.error(`Job ${job.id} (${job.name}) failed: ${err.message}`, err.stack);
49 }
50}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1A single processor can route many job types by branching on the job's name.
  2. 2Reporting progress with updateProgress lets producers and dashboards track long-running work.
  3. 3Worker event hooks like failed centralize error logging across every job the queue handles.

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