How to make a cron job with PM2

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

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);
}

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
  }]
}