MongoDBMonitor.js

"use strict";

const MongoClient = require('mongodb').MongoClient;
const MONGODB_URI = process.env.MONGODB_URI;

let cachedDb = null;

function connectToDatabase (uri) {
    if (cachedDb) {
        return Promise.resolve(cachedDb);
    }
    const dbName = process.env.MONGODB;
    return MongoClient.connect(uri, { useNewUrlParser: true }).then(client => {
        cachedDb = client.db(dbName);
        return cachedDb;
    });
}

function queryDatabase (db) {
    return new Promise(function(resolve, reject) {
        return db.command({ "replSetGetStatus": 1 }, (err, result) => {
            if (err) {
		reject(err);
	    } else {
		resolve(result);
	    }
        });
    });
}

exports.handler = async function(event, context) {
    context.callbackWaitsForEmptyEventLoop = false;
    return connectToDatabase(MONGODB_URI)
    .then(db => queryDatabase(db))
    .then(result => {
        return result.members;
    }).catch(err => {
        return err
    });
};