simple code to show SNS topic subscription, confirmation and notification handling via expressJS

sns-subscription.js

const express = require('express')
const AWS = require("aws-sdk")
var bodyParser = require('body-parser')
const MessageValidator = require('sns-validator')
var jsonParser = bodyParser.json()

const config = {
    "SNS_TOPIC_ARN": "",
    "USER_ARN": "",
    "USER_ACCESS_KEY_ID": "",
    "USER_SECRET_ACCESS_KEY": "",
    "DLQ_ARN": ""
};

// exponential backoff retry times = 20 - 3 - 2 - 5 = 20 - 10 = 10
// 10 times retry  (with exponential backoff from 1 second to 60 seconds)
const deliveryPolicy = {
    "healthyRetryPolicy": {
        "minDelayTarget": 1,
        "maxDelayTarget": 60, // maximum value of 3,600 seconds
        "numRetries": 20, // The total number of retries, including immediate, pre-backoff, backoff, and post-backoff retries. max of 100
        "numNoDelayRetries": 3, // retry 5 times immediately in the no-delay phase
        "numMinDelayRetries": 2, // retry 2 times, 1 second apart in the pre-backoff phase
        "numMaxDelayRetries": 5, // 10 times 60 seconds apart in the post-backoff phase
        "backoffFunction": "exponential"
    },
}

const redrivePolicy = {
    "deadLetterTargetArn": config.DLQ_ARN
}

const app = express()
const port = 3030

app.use(
    express.json({
      type: [
        'application/json',
        'text/plain', // AWS sends this content-type for its messages/notifications
      ],
    })
  )

// const credentials = new AWS.SharedIniFileCredentials({profile: 'sns_profile'});
const SNS = new AWS.SNS({
    credentials: {
        accessKeyId: config.USER_ACCESS_KEY_ID,
        secretAccessKey: config.USER_SECRET_ACCESS_KEY,
    },
    region: 'eu-central-1'
})

app.get('/', (req, res) => {
  res.send({ response: 'Hello World!' })
})

// Endpoint used to create subscription via http request
app.post('/subscribe', (req, res) => {
    let params = {
        Protocol: 'HTTPS', 
        TopicArn: config.SNS_TOPIC_ARN,
        Endpoint: '',
        Attributes: {
            DeliveryPolicy: JSON.stringify(deliveryPolicy),
            RedrivePolicy: JSON.stringify(redrivePolicy)
        },
        ReturnSubscriptionArn: true
    };

    SNS.subscribe(params, (err, data) => {
        if (err) {
            console.log({err, msg: "error subscribing to topic"});
        } else {
            console.log(data);
            res.send({data, msg: "success to topic"});
        }
    });
});

// function used to call the confirmSubscription action on SNS
const confirmSubscription = (request) => {
    console.log('running  confirmSubscription', request.body)
    const { Token, TopicArn } = request.body
    const params = {
        Token,
        TopicArn
    }

    SNS.confirmSubscription(params, function(err, data) {
        if (err) console.log({err, stack: err.stack, message: "error confirming subscription"}); // an error occurred
        else     console.log({data, message:"successfuly confirmed subscription"});           // successful response
    });
}

// The HTTP endpoint registered on AWS for
app.post('/notifications', jsonParser, (req, res) => {
    const validator = new MessageValidator();
    const messageType = req.body.Type

    validator.validate(req.body, function (err, message) {
        if (err) {
            // Your message could not be validated.
            console.log(err, 'error validating message')
            return;
        }
    
        // SNS subscription confirmation
        if (messageType == 'SubscriptionConfirmation') {
            confirmSubscription(req)
            console.log({body:req.body, messageType})
        }
        // SNS notifications
        if (messageType == 'Notification') {
            const { Message} = req.body
            console.log({messageType, Message:JSON.parse(Message)})
        }
    });


    // res.sendStatus(500).send({message: 'cannot process request'})
    res.send("success")
});

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`)
})