Notification Service

Accomplishments

• Architected and led a microservices-based distributed notification system spanning 5 services (API Gateway, User, Email, Push, Template) plus RabbitMQ, Redis, and PostgreSQL, all orchestrated via Docker Compose on an isolated backend bridge network.
• Designed a message-driven, decoupled architecture using a RabbitMQ notifications.direct direct exchange that routes payloads to email.queue or push.queue based on notification_type, with a notification.status queue and a failed.queue dead-letter queue.
• Built the NestJS API Gateway that validates/authenticates incoming requests and publishes them to the appropriate queue via a NotificationService.routeNotification method that asserts a durable exchange and publishes by routing key.
• Refactored the API Gateway to use Prisma for its data layer, added request validation, and added a global ResponseInterceptor to standardize the API response envelope (success, message, data, meta).
• Implemented the FastAPI Email Service consumer that reads from email.queue, enforces idempotency, sends the email, and marks the request processed — using an aio_pika robust connection with QoS prefetch of 10.
• Added Redis-based idempotency (Idempotency.is_processed / mark_processed) keyed on request_id with a configurable TTL (default 1 day) to prevent duplicate email deliveries.
• Implemented an exponential-backoff retry pipeline in the email consumer: failed messages are re-published with an x-retries header up to MAX_RETRIES, then routed to the dead-letter queue for manual inspection.
• Built a reusable async CircuitBreaker (CLOSED/OPEN/HALF states with fail threshold and reset timeout) applied as a decorator around the SMTP send function to prevent hammering a failing provider.
• Implemented async HTML email delivery over Gmail SMTP with STARTTLS via aiosmtplib, including dynamic template rendering by calling the Template Service /templates/render endpoint.
• Built the FastAPI Template Service with versioned template CRUD, code/language lookup, paginated listing, and a /render endpoint that performs variable substitution to produce subject/body.
• Delivered the NestJS Push Service integrating Firebase Cloud Messaging (sendEachForMulticast) for multi-device push, with Redis idempotency (push:{notification_id}), an in-service circuit breaker, and FCM dry-run token validation.
• Implemented the push queue consumer with durable queues, prefetch of 10, exponential-backoff retries (capped at 30s), dead-letter routing after max retries, and publishing delivery/failure status to the notification.status queue.
• Built the NestJS User Service handling authentication (signup/login/JWT), user CRUD, contact info and notification preferences, including a current-user decorator and user-update functionality.
• Added /health endpoints across services and Docker Compose health-check-based dependency ordering (e.g. email-service waits for healthy Postgres/RabbitMQ) for reliable orchestration.
• Containerized every service with individual Dockerfiles and optimized production/multi-stage builds, and authored the comprehensive project README documenting architecture, message-queue setup, request formats, and performance targets (1,000+ notifications/min, 99.5% delivery success).
• Coordinated a multi-contributor workflow via feature branches and pull requests (e.g. push-service, api-gateway-service, user-service, template-service PRs), reviewing and merging others’ work into main.