[BE-04] Configure BullMQ queue infrastructure for async job processing

[yusuftomilola]

Overview

@nestjs/bull and bull are installed in package.json but never configured. Async processing (email sending, report generation, Stellar transactions, notification dispatch) must not block HTTP request handlers. This issue sets up the queue infrastructure that all async features will use.

Context

• package.json has @nestjs/bull@11.0.4 and bull@4.16.5 installed
• Redis connection will be shared with the caching layer (BE-05)
• Queue names should be centralised in a constants file to avoid magic strings across modules
• .env.example needs REDIS_HOST and REDIS_PORT added

Acceptance Criteria

• Add REDIS_HOST (default: localhost) and REDIS_PORT (default: 6379) to backend/.env.example
• Register BullModule.forRootAsync() in AppModule using ConfigService for the Redis connection
• Create src/queue/queue.constants.ts with exported queue name constants (e.g., MAIL_QUEUE, NOTIFICATION_QUEUE, REPORT_QUEUE, STELLAR_QUEUE)
• Create src/queue/queue.module.ts that other modules import to register specific queues
• Verify the queue connects to Redis on app startup with a logged confirmation message
• Document how to add a new queue and processor in a code comment on queue.module.ts

[Henrichy]

@Henrichy has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Sir,
I came across your project and I’m really interested in contributing.
I have experience with React for building responsive, user-friendly interfaces, and I’m also familiar with smart contracts and blockchain basics. I focus on writing clean, scalable code and improving user experience.
I’m a fast learner and ready to get started immediately. Please let me know the next steps.
Thank you.
Best regards,
Henry

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[portableDD]

@portableDD has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

can i work on this?

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[Abba073]

@Abba073 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi maintainer, I would like to work on this issue

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[chidumebiodoh123-cloud]

@chidumebiodoh123-cloud has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I'd like to work on this issue because a well-configured asynchronous job infrastructure is essential for building scalable backend systems. Setting up BullMQ with Redis will allow time-consuming tasks such as email delivery, report generation, notifications, and blockchain transactions to run in the background without impacting API response times. I enjoy designing backend infrastructure that improves performance, reliability, and maintainability while providing a solid foundation for future features.
Relevant experience
I have experience developing backend applications with Node.js, TypeScript, NestJS, Redis, and Bull/BullMQ for asynchronous job processing. I'm familiar with configuring queue modules, managing Redis connections, creating reusable queue abstractions, and implementing background workers for notifications, scheduled tasks, and long-running processes. I have also worked with environment-based configuration, modular application architecture, and logging to ensure queue services are reliable, scalable, and easy to extend.

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This issue has been completed by @portableDD as part of the Stellar Wave Program's 6th Wave 🥳

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