Implementing Job Schedulers in Node.js

Ever wondered how the application server back up the files periodically without any physical interruption. This is where Cron jobs come in.

Cron Jobs schedules a job periodically to do the actions that are configured to do.

there are few use cases where cron jobs play a vital role. they are,

• Deleting Log files - Application generates a lot of logs.clearing old logs will save lots of space in the server. it can be done using cron jobs.
• DB Backup - Database backup saves the application from disasters. Cron job will be helpful to do that.
• Application Logic - we can use cron jobs to do some application logic on a time basis.

How cron job works

we will write a cron job to archive the old records in the database in a production application.

Firstly, create a project and install the following dependencies,

1npm init --yes
2npm install express node-cron mongoose faker

• express - web server library in nodejs
• node-cron - cron job scheduler library in nodejs
• mongoose - ORM for MongoDB

After that, create a file called Model.js and add the following code

1const mongoose = require("mongoose")
2
3const weatherSchema = new mongoose.Schema({
4  minTemp: {
5    type: Number,
6  },
7  maxTemp: {
8    type: Number,
9  },
10  recordedDate: {
11    type: Date,
12  },
13  isArchived: {
14    type: Boolean,
15    default: false,
16  },
17})
18
19class Weather {
20  static getRec(date) {
21    return this.find({
22      recordedDate: {
23        $lte: new Date(date),
24      },
25    }).exec()
26  }
27
28  static insertBulkData(data) {
29    return this.insertMany(data)
30  }
31
32  static archiveData(date) {
33    return this.updateMany(
34      {
35        recordedDate: {
36          $lte: new Date(date),
37        },
38      },
39      {
40        $set: {
41          isArchived: true,
42        },
43      }
44    ).exec()
45  }
46
47  static getArchivedData() {
48    return this.find({
49      isArchived: true,
50    }).exec()
51  }
52}
53
54weatherSchema.loadClass(Weather)
55
56module.exports = mongoose.model("Weather", weatherSchema)

Mainly, Model.js creates a mongoose schema for a DB table which stores the weather data in the database.

After that, create a file called scheduler.js and add the code for job scheduler.

1cron.schedule("* * * * * *", () => {
2  console.log("Running every minute")
3})

cron schedule schedules the job for time format that is mentioned.

To learn more about cron job format, there is a great site crontab-guru which explains in detail

Connect the mongoose with the Express to insert some dummy data to database.

1const cron = require("node-cron")
2const express = require("express")
3const mongoose = require("mongoose")
4const app = express()
5const faker = require("faker")
6const model = require("./Model")
7
8mongoose
9  .connect("mongodb://localhost:27017/nodescheduler")
10  .then(res => {
11    console.log("mongoose connected successfully")
12
13    app.get("/insertdata", async (req, res) => {
14      let data = []
15      for (let i = 0; i < 100; i++) {
16        let record = {
17          minTemp: faker.random.number(),
18          maxTemp: faker.random.number(),
19          recordedDate: faker.date.past(),
20        }
21        data.push(record)
22      }
23
24      await model.insertBulkData(data)
25
26      res.send("Data is inserted")
27    })
28
29    app.listen(4000, () => {
30      console.log("Server is running port 4000")
31    })
32  })
33  .catch(err => {
34    console.error(err)
35  })

To insert some dummy data using fakerjs. run the script with the command, and visit the URL http://localhost:4000/insertdata

1node scheduler.js

it will create some bulk dummy data to test the job scheduler. Now it is time to add the job scheduler.

1cron.schedule("* * * * */3 *", async () => {
2  var d = new Date()
3  d.setMonth(d.getMonth() - 2) //1 month ago
4
5  await model.archiveData(d)
6
7  console.log("scheduler => archived")
8})

Above cron job will run every 3 months, to mark the data as archived in the database.

Likewise, we can use cron jobs to schedule a job for our application logics.

Summary

Above all, cron jobs play a vital role in some application development use cases. it is always good to know how cron jobs work in application development.