How to call another process when AWS Context callbackWaitsForEmptyEventLoop = false - mongodb

Question

I'm using the best practice MongoDB with Lambda example from here https://docs.atlas.mongodb.com/best-practices-connecting-to-aws-lambda/
I need to publish to SNS but are unable to due to the callbackWaitsForEmptyEventLoop = false, if I uncomment this, it works fine but then my Lambda function just times out and never receive the success callback.
"use strict";
const MongoClient = require('mongodb').MongoClient;
const MONGODB_URI = process.env.MONGODB_URI; // or Atlas connection string
const AWS = require('aws-sdk');
const SNS_TOPICARN = process.env.SNS_TOPICARN;
const sns = new AWS.SNS({ apiVersion: '2010-03-31' });
let cachedDb = null;
function connectToDatabase(uri) {
console.log('=> connect to database');
if (cachedDb) {
console.log('=> using cached database instance');
return Promise.resolve(cachedDb);
}
return MongoClient.connect(uri)
.then(db => {
cachedDb = db;
return cachedDb;
});
}
function queryDatabase(db) {
console.log('=> query database');
return db.collection('items').find({}).toArray()
.then((data) => { return { statusCode: 200, data: data }; })
.catch(err => {
console.log('=> an error occurred: ', err);
return { statusCode: 500, data: null };
});
}
exports.handler = (event, context, callback) => {
context.callbackWaitsForEmptyEventLoop = false;
console.log('event: ', event);
connectToDatabase(MONGODB_URI)
.then(db => queryDatabase(db))
.then(result => {
console.log('=> returning result: ', result);
var params = {
Message: result.data,
Subject: 'Devices Lost Connection',
TopicArn: SNS_TOPICARN
};
sns.publish(params, function (err, data) {
if (err) console.log(err, err.stack);
else console.log(data);
});
callback(null, result);
})
.catch(err => {
console.log('=> an error occurred: ', err);
callback(err);
});
};

Answer 1

Problem solved, will leave it here if someone else has the same issue:
I need to do the handler callback in the callback of the second function:
sns.publish(params, function (err, data) {
if (err) console.log(err, err.stack);
else console.log(data);
callback(null, result);
});