app_final.js

'use strict'
const AWS = require('aws-sdk');
var MongoClient = require('mongodb').MongoClient;

let atlas_connection_uri;
let cachedDb = null;

exports.handler = (event, context, callback) => {
    var uri = process.env['MONGODB_ATLAS_CLUSTER_URI'];

    if (atlas_connection_uri != null) {
        processEvent(event, context, callback);
    }
    else {
        const kms = new AWS.KMS();
        kms.decrypt({ CiphertextBlob: new Buffer(uri, 'base64') }, (err, data) => {
            if (err) {
                console.log('Decrypt error:', err);
                return callback(err);
            }
            atlas_connection_uri = data.Plaintext.toString('ascii');
            processEvent(event, context, callback);
        });
    }
};

function processEvent(event, context, callback) {
    console.log('Calling MongoDB Atlas from AWS Lambda with event: ' + JSON.stringify(event));
    var jsonContents = JSON.parse(JSON.stringify(event));

    //the following line is critical for performance reasons to allow re-use of database connections across calls to this Lambda function and avoid closing the database connection. The first call to this lambda function takes about 5 seconds to complete, while subsequent, close calls will only take a few hundred milliseconds.
    context.callbackWaitsForEmptyEventLoop = false;

    //date conversion for grades array
    if (jsonContents.grades != null) {
        for (var i = 0, len = jsonContents.grades.length; i < len; i++) {
            //use the following line if you want to preserve the original dates
            //jsonContents.grades[i].date = new Date(jsonContents.grades[i].date);

            //the following line assigns the current date so we can more easily differentiate between similar records
            jsonContents.grades[i].date = new Date();
        }
    }

    try {
        if (cachedDb == null) {
            console.log('=> connecting to database');
            MongoClient.connect(atlas_connection_uri, function (err, db) {
                cachedDb = db;
                return createDoc(db, jsonContents, callback);
            });
        }
        else {
            createDoc(cachedDb, jsonContents, callback);
        }
    }
    catch (err) {
        console.error('an error occurred', err);
    }
}

function createDoc(db, json, callback) {
    db.collection('restaurants').insertOne(json, function (err, result) {
        if (err != null) {
            console.error("an error occurred in createDoc", err);
            callback(null, JSON.stringify(err));
        }
        else {
            console.log("Kudos! You just created an entry into the restaurants collection with id: " + result.insertedId);
            callback(null, "SUCCESS");
        }
        //we don't need to close the connection thanks to context.callbackWaitsForEmptyEventLoop = false (above)
        //this will let our function re-use the connection on the next called (if it can re-use the same Lambda container)
        //db.close();
    });
};