How to make a cron job with PM2

Question

I want to make a cron job to send mail every 15 minutes taking data from a database table. In node js I can make a cron job but through PM2 I don't understand where to place the code and how it works.

Answer 1

Use the --cron option:

-c --cron <cron_pattern>

For example:

pm2 start sendMail.js --cron "*/15 * * * *"

Pm2 will now restart the sendMail.js script on the hour, and at 15, 30 and 45 minutes past the hour

Answer 2

If you use PM2 ecosystem then in the config file add cron sequence to script param by wrapping it with single quotes. Somehow double quotes didn't work for me.

module.exports = {
  apps : [{
    name        : "Send-mail",
    script      : "./sendMail.js --cron '*/15 * * * *'",
    watch       : true
  }]
}

alternatively (my preference)

module.exports = {
  apps : [{
    name        : "Send-mail",
    script      : "./sendMail.js",
    cron_restart: "*/15 * * * *",
    watch       : true
  }]
}

Answer 3

This is what worked for me, I split the cron in a different file which runs in a different process because i want to free up resources after cron has completed execution.

ecosystem.config.js:

module.exports = {
  /**
   * Application configuration section
   * http://pm2.keymetrics.io/docs/usage/application-declaration/
   */
  apps: [

    // Main API Hosting
    {
      name: 'API',
      script: 'bin/www',
      env: {
        COMMON_VARIABLE: 'true'
      },
      instances: 1,
      exec_mode: 'cluster',
      watch: false,
      autorestart: true
    },
    {
      name: 'CRON',
      script: "crons/cronjob.js",
      instances: 1,
      exec_mode: 'fork',
      cron_restart: "0,30 * * * *",
      watch: false,
      autorestart: false
    }
  ]
};

The following lines are important in the cron executable

cron_restart: "0,30 * * * *" <- cron expression

autorestart: false <- important because otherwise pm2 will restart the cron after completion immediately

Also make sure your instances is 1 otherwise multiple cron processes will run.

Key caveats:

Whenever you do pm2 restart all, the cron job will run irrespective of the cron expression. If Its critical to run only at specific times, add this additional check in the beginning of the cron file

if (new Date().getHours() !== 0 ) {
  console.log(`Current hours is ${new Date().getHours()}, not running.`)
  process.exit(0);
}

Answer 4

You can also use the node-schedule module which allows you to define cron style rules. Then, you can run the program normally in pm2, I use this with PM2 for a lot of projects and it has never let me down.

var schedule = require('node-schedule');

var rule = new schedule.RecurrenceRule();
rule.hour = [10]; // 10am
rule.minute = [0]; // 0mins

var job = schedule.scheduleJob(rule, function(){
    console.log("10am every day")
});         

//Rule 2 - 6am every wednesday
var rule2 = new schedule.RecurrenceRule();
rule2.dayOfWeek = 3; // 0 = Sunday
rule2.hour = 6;
rule2.minute = 0;

var job2 = schedule.scheduleJob(rule2, function(){
    console.log("Every Wednesday @ 6am");
});


var rule3 = new schedule.RecurrenceRule();
rule3.minute = [0, 15, 30, 45]; // Specific Minutes

var job3 = schedule.scheduleJob(rule3, function(){
    console.log("Run at specific minutes")
});         

It also supports CRON style rules, but I prefer the above method.

Check out the documentation at https://www.npmjs.com/package/node-schedule

Answer 5

thank you for your answer; i do it in this way and just set the email

1. npm install node-crontab

2. var crontab = require('node-crontab');

var jobId = crontab.scheduleJob("*/15 * * * *", function(){

//This will call this function every 15 minutes

console.log("It's been 15 minutes!");

});