MongoBackupScript.js

/*
Problem Statement:
- To have a cost-effective data backup backup mechanism for mongodb on a daily basis.

Solution:
- To write a cron job that will backup data from all collections of a mongo db and store it on the server
- 7 days of backup will be maintained at any given point of time (post 7 days of successful backup). This is done so that the DB could be restored to any day in the last 7 days.
- Appropriate success/failure logs are maintained for further debugging.
- Alos log the number of records that are backed up.
- Library used:
    - `sails-hook-cron` : provides method to write a cron job
    - `async` : to carry out asynchronous operations
    - `fs` : for accessing file storage
    - ``moment` : to name file based on the day of the week
*/

const async = require("async");
const fs = require('fs');
const moment = require('moment');

module.exports.cron = {
    backup: {
        //Backup scheduled for every day at 00:00 AM
        schedule: '0 0 0 * * *',
        onTick: function() {
            //Get all modelNames
            const models = Object.keys(sails.models).filter((item) => {
                return item !== "archive"
            });
            let backup = {};
            
            //Get all data from models and save it in backup
            async.mapLimit(models, models.length,
                (modelName, cb) => {
                    sails.models[modelName].find({}).exec((err, result) => {
                        if (err) {
                            cb(err, null);
                        } else if (result) {
                            backup[modelName] = result;
                            cb(null, `${modelName} has ${result.length} records`);
                        }
                    });
                }, (err, results) => {
                    backup.logs = results
                    backup.time = new Date();
                    //To store 7 days of backup at most. Backups after that will be overridden.
                    fs.writeFileSync(`.tmp/public/backup${moment().isoWeekday()}.json`, JSON.stringify(backup));
                }
            )
        },
        start: true
    }
};