Serverless Notification service

This AWS Cloudformation stack can serve as your notifier stack to send SMS and EMAIL. Since its serverless it can scale out/in when needed without any manual configuration.

Features

• Serverless so nothing to manage, its scalable, more flexible and quick to release with pay as you go model.
• Auto retrial in case of failures
• Can handle email of any size . This depends on your mail server limit. Eg: AWS SES allows 10MB max.
• Transactional type can be used for quick delivery of messages within seconds
• Promotional type can be used for sending promotional or delayed communication
• One can add its own implementation or vendor lib to send SMS/EMAIL
• Using aws cdk for defining cloud infrastructure as code a.k.a IAC so your infra too is version controlled as part of your application repository along with other benefits.
• Each request is logged into CW for future analysis and debugging

Getting Started

Install cdk

npm install -g aws-cdk-lib

Deploy CDK toolkit stack in your aws environment Ref

cdk bootstrap --qualifier $randomString --profile $awsprofile $aws_account_id/$aws_region

Creating cdk project

To satisfy all dependencies of this project including tools like typescript compiler and cdk toolkit from local project folder instead of global we would be using npx. Ref

npx aws-cdk init --language typescript

Setting default AWS profile with appropiate IAM permissions for deployment

export AWS_DEFAULT_PROFILE="profilename"

Create cdk shortcut

alias cdk="npx aws-cdk"

Passing environment variables for deployment

You can set your environment variable in cdk.context.json OR pass directly from command line

PROJECT_NAME=notifier DEPLOYMENT_REGION=ap-south-1 DEPLOYMENT_ENV=dev cdk deploy

Security

For demo purpose current AuthType for Router lambda function URL is set to NONE but in production you should set it to AWS_IAM and make sure caller has lambda:InvokeFunctionUrl permission. Ref

Rest Endpoints and payload

Method	Function URL	Payload
POST	{fnURL}/sms	{ "message":"Your message", "mobileNos":["xxxxxxx"], "type":"PROMOTIONAL" }
POST	{fnURL}/email	{ "htmlMailBody":"Welcome to email testing", "subject":"Test Subject", "type":"TRANSACTIONAL", "toEmailIds":["xxxxx"], "ccEmailIds":["xxxx"], "attachments":[ "content":"'base64content", "fileName":"image.jpg" ]}

• Refer RouterLbdFunctionURL in Cfn output section for fnURL
• By changing application code in resources folder you can customize your payload if needed
• Make sure caller has appropiate IAM permission to call api endpoint. Ref

Customization

• Function defination to send SMS/EMAIL is commented so that one can write their own implementation.
• Check index.js files in resources/promotional and resources/transactional folders

Message retrial configuration

• Message can be of two types TRANSACTIONAL or PROMOTIONAL

• TRANSACTIONAL

  • Messages of this type are delivered within seconds
  • They are retried every 15 sec until retention period (3 min) expires or message is being deleted
  • They are poped as soon as they are avaliable in queue

• PROMOTIONAL

  • Messages of this type are delivered in few minutes
  • They are retried every 5 min until retention period expired or message is being deleted
  • They are processed in batches of 10 and batchWindow of 1min

• Message are auto delete from queue if lambda return success

Future enhancements

• This stack is using AWS Lambda function URL to generate REST API endpoint but if you need advance features like realtime limit tracking,advance throttling,caching,websockets etc we can use API Gateway instead.
• Env driven retrial configuration
• Upload to S3 when msg size is greater than 256KB

Testing Lambdas

• In order to test lambda locally make sure you have docker and AWS SAM cli installed
• Ref: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-cdk-testing.html

Useful cdk commands

• npm run build compile typescript to js
• npm run watch watch for changes and compile
• npm run test perform the jest unit tests
• cdk deploy deploy this stack to your default AWS account/region
• cdk diff compare deployed stack with current state
• cdk synth emits the synthesized CloudFormation template