Resilient Email Sending Service

A robust email delivery service with built-in reliability patterns including retries, circuit breakers, rate limiting, and failover between multiple providers.

Table of Contents

• Features
• Architecture
• Tech Stack
• Local Setup
• Testing
• Deployment
• Contributing
• License

Features

Core Functionality

• 📧 Multi-provider email delivery (Primary + Secondary)
• 🔄 Automatic failover between providers
• 🔁 Configurable retry mechanism with exponential backoff

Reliability Patterns

• ⚡ Circuit Breaker implementation
• 🚦 Rate limiting
• 🔑 Idempotency support
• 📊 Status tracking for all sent emails

Monitoring

• 📝 Detailed logging
• 🔍 Email status lookup
• ⚠️ Provider health monitoring

Architecture

graph TD
    A[Client] -->|Send Request| B[Email Service]
    B --> C{Primary Provider}
    C -->|Success| D[Return Success]
    C -->|Failure| E[Circuit Breaker]
    E -->|Open| F{Secondary Provider}
    F -->|Success| D
    F -->|Failure| G[Return Error]
    B --> H[Rate Limiter]
    B --> I[Idempotency Check]

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Test Details

Tech Stack

Backend:

• Node.js
• TypeScript
• Express

Reliability Patterns:

• Circuit Breaker
• Exponential Backoff Retry
• Token Bucket Rate Limiting
• Idempotency Keys
• Simple logging
• Fallback mechanism to switch providers

Testing:

• Jest
• ts-jest
• Supertest

Local Setup

Prerequisites

• Node.js v16+
• npm/yarn
• TypeScript

Installation

1. Clone the repository:

   git clone https://github.com/jasjeev013/email-service.git
   cd email-service

2. Install dependencies:

   npm install

3. Configure environment variables (create .env file):

   PORT=3000 // Optional
   RATE_LIMIT_WINDOW_MS=60000 // Optional
   RATE_LIMIT_MAX=10 // Optional

Running the Service

Start the development server:

npm run dev

The service will be available at:

http://localhost:3000

Testing

Run unit tests:

npm test

Run tests with coverage:

npm test -- --coverage

Test watch mode:

npm run test:watch

Test Cases

• Provider failure scenarios
• Rate limiting behavior
• Circuit breaker state transitions
• Idempotency checks
• Retry logic validation

Deployment

Vercel

1. Install Vercel CLI:

   npm install -g vercel

2. Deploy:

   vercel

Docker

Build the Docker image:

docker build -t email-service .

Run the container:

docker run -p 3000:3000 email-service

Contributing

1. Fork the project
2. Create your feature branch (git checkout -b feature/AmazingFeature)
3. Commit your changes (git commit -m 'Add some AmazingFeature')
4. Push to the branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

License

Distributed under the MIT License. See LICENSE for more information.

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GitHub Repo • Live Demo

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