Introduction

The Notification service is a serverless AWS Lambda microservice responsible for sending email and SMS notifications. It is event-driven — it receives events from EventBridge (published by the API) and routes them to the appropriate notification channels.

Responsibilities

• Send transactional emails (registration, password reset, email verification) via Resend
• Send SMS messages via Twilio
• Render email templates using React Email
• Map domain events to notification strategies

Architecture

The service uses three layers:

Strategies Each domain event maps to a strategy (e.g., UserWasCreated, AuthTokenWasCreated). The strategy defines which channels to notify and what content to send.

Channels Channels abstract the delivery mechanism: EmailChannel, SmsChannel, PushChannel. Each channel delegates to a provider.

Providers Providers are thin wrappers around third-party SDKs:

• ResendEmailProvider — sends email via the Resend API
• TwilioSmsProvider — sends SMS via Twilio

EventBridge Event
      │
  Lambda Handler
      │
  NotificationRegistry  ──  looks up strategy by event type
      │
  NotificationStrategy  ──  defines channels + content
      │
  Channel (Email / SMS)
      │
  Provider (Resend / Twilio)

Email templates

Email templates are built with React Email and @react-email/components. Templates are rendered to HTML at runtime inside the Lambda, so no separate rendering service is needed.