Wednesday, 30 May, 2018 UTC
Summary
Ever wanted to do specific things on your application server at certain times without having to physically run them yourself. You want to spend more of your time worrying about productive tasks instead of remembering that you want to move data from one part of the server to another every month. This is where Cron jobs come in.
In your Node applications, the applications of these are endless as they save. In this article, we’ll look at how to create and use Cron jobs in Node applications. To do this, we’ll make a simple application that automatically deletes auto-generated
Prerequisites
error.log files from the server. Another advantage of Cron jobs is that you can schedule the execution of different scripts at different intervals from your application.To follow through this tutorial, you’ll need the following:
- Node installed on your machine
- NPM installed on your machine
- Basic knowledge of JavaScript
To get started, create a new Node application by opening your terminal and creating a new folder for your project. Then initialize it by running the commands:
mkdir cron-jobs-node cd cron-jobs-node
npm init -yTo make this application work we are going to need a couple of dependencies. You can install them by running the following commands:
npm install express node-cron fsexpress - powers the web servernode-cron - task scheduler in pure JavaScript for node.jsfs - node file system moduleCreate an
index.js file and then import the necessary node modules: touch index.jsEdit the
index.js file to look like this: // index.js
const cron = require("node-cron");
const express = require("express");
const fs = require("fs");
app = express();
[...]Now here’s where
node-cron comes in. After a while, we want to delete the error log files at intervals without having to do it physically. We will use node-cron to do this. Let’s take a look a simple task first. Add the following to your index.js file: // index.js
[...]
// schedule tasks to be run on the server
cron.schedule("* * * * *", function() {
console.log("running a task every minute");
});
app.listen(3128);
[...]Now, when we run the server, we get the following result:
> node index.js
running a task every minute
running a task every minuteWith
node-cron, we can schedule tasks for different intervals. Let’s see how to schedule task using different intervals. In the example above, we created a simple Cron job, the parameters passed to the .schedule() function were * * * * * . These parameters have different meanings when used: * * * * * *
| | | | | |
| | | | | day of week
| | | | month
| | | day of month
| | hour
| minute
second ( optional )Using this example, if we want to delete the log file from the server on the 21st of every month, we update the
index.js to look like this: // index.js
const cron = require("node-cron");
const express = require("express");
const fs = require("fs");
app = express();
// schedule tasks to be run on the server
cron.schedule("* * 21 * *", function() {
console.log("---------------------");
console.log("Running Cron Job");
fs.unlink("./error.log", err => {
if (err) throw err;
console.log("Error file succesfully deleted");
});
});
app.listen("3128");Now, when the server is run, you get the following output:
NB: To simulate the tasks, intervals were set to shorter period by setting the number of minutes in the parameter for the task scheduler
You can run any actions inside the scheduler. Actions ranging from creating a file, to sending emails and running scripts. Let’s take a look at more use cases
Use Case 2 - Backing Up Database
Ensuring the accessibility of user data is very key to any business. If an unforeseen event happens and your database becomes corrupt, all hell will break loose if you don’t have any form of existing backup for your business. To save yourself the stress in the occurrence of such, you can also use Cron jobs to periodically backup the existing data in your database. Let’s take a look at how to do this.
For the ease of explanation, we are going to use SQLite database
First, we need to install a node module that allows us to run shell scripts:
npm install shelljsAnd also install SQLite if you haven’t:
npm install sqlite3Now create a sample database by running the command:
sqlite3 database.sqliteTo backup your database at 11:59pm every day, update your
index.js file to look like this: // index.js
const fs = require("fs");
let shell = require("shelljs");
const express = require("express");
app = express();
// To backup a database
cron.schedule("59 23 * * *", function() {
console.log("---------------------");
console.log("Running Cron Job");
if (shell.exec("sqlite3 database.sqlite .dump > data_dump.sql").code !== 0) {
shell.exit(1);
}
else{
shell.echo("Database backup complete");
}
});
app.listen("3128");Now, when you run the server using the command:
node index.jsYou get the following result:
Use Case 3 - Sending emails every n-time interval
You can also use Cron jobs to keep your users up to date as to what is going on with your business by sending them emails at different intervals. For example, you can curate a list of interesting links and then send them to users every Sunday. To do something like this, you’ll need to do the following.
Install nodemailer by running the command:
npm install nodemailerOnce that is done, update the
index.js file to look like this: // index.js
const cron = require("node-cron");
const express = require("express");
let nodemailer = require("nodemailer");
app = express();
// create mail transporter
let transporter = nodemailer.createTransport({
service: "gmail",
auth: {
user: "[email protected]",
pass: "userpass"
}
});
// sending emails at periodic intervals
cron.schedule("* * * * Wednesday", function(){
console.log("---------------------");
console.log("Running Cron Job");
let mailOptions = {
from: "[email protected]",
to: "[email protected]",
subject: `Not a GDPR update ;)`,
text: `Hi there, this email was automatically sent by us`
};
transporter.sendMail(mailOptions, function(error, info) {
if (error) {
throw error;
} else {
console.log("Email successfully sent!");
}
});
});
app.listen("3128");NOTE: You will need to temporarily allow non-secure sign-in for your Gmail account for testing purposes here
Now, when you run the server using the command
Conclusion
node index.js , you get the following result:In this article, we have seen an introduction to Cron jobs and how to use them in your Node.js applications. Here’s a link to the GitHub repository. Feel free to add a suggestion or leave a comment below.