Email Service

Intro

A simple HTTP REST api:

• Sends emails using multiple providers (Sendgrid & Mailgun)
• Provides failover if one of the provider fails

Environment

• node 8
• npm 5

Schema

• Refer to swagger

Failover Approach

• The config has a default provider preference order set e.g. ['mail-gun', 'send-mail']. so in this case mail-gun is the preferred provider
• The Email sender loops on the available providers in order of preference and tries to send email sender
• If there is a failure while sending the email it updates the current provider to be of lower priority provider-preference
• It then tries to send the email with next provider
• The approach can be improved further to switch back to the the original preferred provider after some time to retry

Metrics

• The api exposes some simple metrics at GET /metrics for number of emails sent or failed
• e.g.

  {
    email: {
      sent: 5,
      fail: 1
    }
  }

Routes

Path	Method
/email	POST
/health-check	GET
/metrics	GET

Project Structure

├── src - service source files
|      ├── schemas - schema validators
|      ├── email - email routes and external provider services
├── test - (using mocha/shouldjs/nock)
       ├── integration
       ├── unit

Quick Setup

1. Clone the repo
2. npm i to install node packages
3. Run MAIL_GUN_API_KEY=<> SEND_GRID_API_KEY=<> npm start to start the app
4. View logs at tail -f email-service.log
5. Run npm test to run specs
6. Run npm run lint to run es6 linter

Config

1. App config is at src/config.js
2. Set Environment variables for mail provider api keys:
   • MAIL_GUN_API_KEY
   • SEND_GRID_API_KEY

Sample Request

curl -X POST \
  http://localhost:3000/email \
  -d '{
  "to": ["john.doe@gmail.com"],
  "cc": ["john.doe@yahoo.com"],
  "subject": "test-email",
  "body": "test email content"
}'

Pending

• can store email sent details in database to track and show
• log metrics - num of emails sent by provider, num of failures by provider
• handling more request validation scenarios for different providers
• more integration tests can be added to cover scenarios