Cron jobs & task scheduling

Let’s go through cron jobs and task scheduling in Node.js, which is essential for running periodic tasks, background jobs, or automation.

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1️⃣ What Are Cron Jobs?

• Cron jobs = scheduled tasks that run automatically at specific intervals.

• Useful for tasks like:

  • Sending emails or notifications

  • Cleaning temporary files

  • Database maintenance or backups

  • Fetching API data periodically

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2️⃣ Using node-cron

Install

npm install node-cron

Basic Usage

const cron = require("node-cron");
 
// Schedule a task to run every minute
cron.schedule("* * * * *", () => {
  console.log("Task running every minute:", new Date().toISOString());
});

Cron Syntax

*    *    *    *    *  
┬    ┬    ┬    ┬    ┬
│    │    │    │    │
│    │    │    │    └ day of week (0 - 7) (Sunday=0 or 7)
│    │    │    └───── month (1 - 12)
│    │    └────────── day of month (1 - 31)
│    └─────────────── hour (0 - 23)
└──────────────────── minute (0 - 59)

• Example: 0 9 * * * → every day at 9:00 AM

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Example: Daily Task

cron.schedule("0 0 * * *", () => {
  console.log("Running a daily task at midnight");
});

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3️⃣ Using setInterval for Simple Scheduling

• For simple repeating tasks, you can use Node’s built-in setInterval:

setInterval(() => {
  console.log("Running task every 10 seconds");
}, 10000);

• Limitation: No cron-like scheduling, only interval-based

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4️⃣ Advanced Task Scheduling: bull + Redis

• For robust background jobs with retry, queueing, and concurrency, use Bull:

npm install bull

Example: Queue Job

const Queue = require("bull");
const myQueue = new Queue("emailQueue", "redis://127.0.0.1:6379");
 
// Add a job
myQueue.add({ email: "user@example.com" }, { repeat: { cron: "0 9 * * *" } });
 
// Process jobs
myQueue.process(async (job) => {
  console.log("Sending email to:", job.data.email);
});

• Features:

  • Retry failed jobs

  • Concurrency control

  • Persistent queues

  • Delayed/repeating jobs

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5️⃣ Best Practices

1. Use node-cron for simple periodic tasks

2. Use Bull / Bee-Queue for robust background processing

3. Avoid blocking the main thread in cron jobs → use async tasks or child processes

4. Log task execution for monitoring and debugging

5. Use environment-specific scheduling → avoid running heavy tasks in development

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✅ Summary

Task Type	Tool / Method	Notes
Simple periodic tasks	node-cron	Cron-like scheduling
Repeating intervals	setInterval	Lightweight, interval-based
Background jobs / queues	bull + Redis	Robust, retries, concurrency
Best practice	Async tasks, logging	Avoid blocking main thread

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