Notification Service

This is a notification service that can send multi channel bulk notifications.

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💬 Content

Workflow Diagram:

Technologies, Services and Libraries used:

• Express: Web server
• Bull: Queue manager
• Axios: HTTP client
• Redis: for Bull (queue management)
• Twilio: SMS service provider
• Mailjet: Email service provider

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🏃‍♂️ How to Start

1. Create .env file on the project directory and copy the content from the given link.
2. Install dependencies: yarn install
3. Run the server: yarn dev
4. To run unit tests, run: yarn test
5. Please read the next section to know more about the service and triggers ⬇️⬇️⬇️

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⚠️ Important Notes

• If .env file content is copied from the given link, it should contains all the API keys needed to connect to the Redis Cloud Server (free trial), Twilio SMS service (free trial) and MailJet mail service (free trail).
• Kindly change the phone and email on the user database to receive the notifications. Know More here, User Database.
• Check the Routinely check and send notifications to know how to periodically trigger the notification service.

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📙 Features Brief

1. User Database:

• A json file is considered as the users database, which can be found at data/users.json
• Database structure:

{
    "name": "Test User",
    "sms": "+911234567890",
    "email": "testuser@gmail.com",
    "subscriptions": [
      {
        "topic": "weather",
        "method": "sms"
      }
    ]
  }

2. Routinely check and send notifications:

• To demonstrate this feature, a weather notification service is available, which periodically checks for current weather temperature and sends it to all the subscribed users.
• To start the weather notifier, set RUN_WEATHER_NOTIFIER=true on .env
• It is a cron job which triggers the notifier periodically.
• Trigger frequency can be modified on the index.ts file at line number 8 by passing cron expressions on to the function weatherSchedule.
• Here are some useful cron expressions that can be used:
  • */30 * * * * * : trigger every 30 second
  • */1 * * * * : trigger every minute
  • */5 * * * * : trigger every 5 minute
• Please note, very less frequency triggers can cause sending multiple sms and emails to the recipient address.

3. Flexible to accommodate new mediums:

• SMS and Email service is implemented on the current version of the application. SMS service uses Twilio and Email service uses MailJet.
• Services are dynamically managed by the NotifierManager which keeps track of all the registered notification mediums.
• Because of it's plugin like structure, any new notification mediums can be added very easily with few lines of code.

4. Send notification using a selected medium:

• Notification sending process is managed by a Queue Manager (Bull). It helps in keeping track of all the scheduled notifications and bulk sending process.
• Ad-hoc notification sending process is also available. Please refer to the Send ad-hoc notifications section.

5. Retry send a notification if failed due to some code exception:

• Bull is setup to retry each notification 5 times in case of failure, in 1 seconds interval. In case all 5 tries are failed, it rejects the notification. The retry configuration is customizable.

6. Send ad-hoc notifications

• Ad-hoc notifications can be sent using the REST APIs. More details about the REST APIs can be found in the REST APIs section.

7. Easy to test:

• Each part of the application is defined in a separate module. The entire Notification Service has two main modules.
  • Notifier
  • Scheduler
• Unit test files are available in the test directory. Service specific unit test files are available in their respective directories inside services/.
• More details about the working process of the modules can be found on the Workflow Diagram added at the top of the page.

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💻 REST APIs

for sending ad-hoc notifications

Send a single notification

Request

POST /notifier/send

curl -X POST \
'http://localhost:3030/notifier/send' \
--header 'Accept: */*' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'service=sms' \
--data-urlencode 'message=Hello World' \
--data-urlencode 'to=${your_mobile_number}'

Response

HTTP/1.1 200 OK
Date: Sun, 24 Apr 2022 20:28:58 GMT
Status: 200 OK
Connection: close
Content-Type: application/json; charset=utf-8
Content-Length: 23
x-powered-by: Express

{
  "status": "success",
  "message": "Notification sent!"
}

Send bulk notification to a topic

Request

POST /notifier/sendToTopic

curl -X POST \
  'http://localhost:3030/notifier/sendToTopic' \
  --header 'Accept: */*' \
  --header 'Content-Type: application/x-www-form-urlencoded' \
  --data-urlencode 'topic=weather' \
  --data-urlencode 'messages=[{"message":"Hello World","service":"sms"},{"message":"Hello Folks, How are you doing?","service":"email"}]'

Response

HTTP/1.1 200 OK
Date: Sun, 24 Apr 2022 20:28:58 GMT
Status: 200 OK
Connection: close
Content-Type: application/json; charset=utf-8
Content-Length: 56
x-powered-by: Express

{
  "status": "success",
  "message": "Notification scheduled!"
}

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Thank you for reading.