Node-cron Simple to Complex Setup with PM2

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Cách tạo scheduled jobs với node-cron, phân biệt Express vs Worker processes, và quản lý với PM2 ecosystem

📋 Table of Contents

⁠

Giới Thiệu⁠

⁠

Khái Niệm Cơ Bản⁠

⁠

Phase 1: Simple Cron (Console Log)⁠

⁠

Phase 2: Database Integration⁠

⁠

Phase 3: Production Worker⁠

⁠

Express vs Worker Processes⁠

⁠

PM2 Ecosystem Management⁠

⁠

Best Practices⁠

⁠

Troubleshooting⁠

⁠

🎯 Giới Thiệu

Cron là gì?

Cron = Công cụ schedule tasks (jobs) chạy tự động theo lịch trên server.

Use cases:

Gửi email theo lịch

Backup database định kỳ

Cleanup old data

Generate reports

Sync data từ API

Send notifications

⁠

node-cron là gì?

node-cron = JavaScript library để tạo cron jobs trong Node.js

So với Linux crontab:

Feature

Linux crontab

node-cron

Syntax

* * * * *

* * * * * (giống)

Language

Shell/Bash

JavaScript/Node.js

Database access

Khó

Dễ (Sequelize, etc)

Error handling

Khó

Dễ (try-catch)

Logging

File system

Winston, console

Deployment

System level

App level

There are no rows in this table

⁠

🧠 Khái Niệm Cơ Bản

1. Cron Syntax

Ví dụ:

⁠

2. Process vs Thread

Process = 1 chương trình đang chạy độc lập

Đặc điểm:

Mỗi process có memory riêng

Chạy độc lập, không ảnh hưởng nhau

Crash 1 process ≠ crash tất cả

Có PID riêng (Process ID)

⁠

🔰 PHASE 1: Simple Cron (Console Log)

Mục tiêu: Hiểu cơ bản về cron

Step 1: Install

⁠

Step 2: Tạo Simple Worker

File: workers/simpleWorker.js

⁠

Step 3: Test

Output:

✅ Success! Bạn đã tạo cron job đầu tiên!

Press Ctrl+C để stop.

⁠

Step 4: Multiple Schedules

⁠

📝 PHASE 2: Database Integration

Mục tiêu: Ghi logs vào MySQL database

Step 1: Setup Database (ví dụ Sequelize)

⁠

Step 2: Tạo DB Worker

⁠

Step 3: Test DB Worker

Terminal 1: Run worker

Output:

Terminal 2: Check database

Result:

✅ Success! Worker đang ghi vào database!

⁠

🚀 PHASE 3: Production Worker

Mục tiêu: Tạo real-world email worker với error handling, retry logic

Architecture:

⁠

Step 1: Database Schema

Table: job_queue

⁠

Step 2: Email Worker

File: workers/emailWorker.js

⁠

Express vs Worker Processes

Khái Niệm Cốt Lõi

Express App và Worker là 2 Node.js processes RIÊNG BIỆT:

⁠

Comparison Table

Aspect

Express App

Worker Process

File

app.js / server.js

workers/emailWorker.js

Purpose

Handle HTTP requests

Run background jobs

Port

Listen on port (3000)

No port needed

Triggered by

User requests

Cron schedule

Process

1 separate process

Memory

Own memory space

Crash impact

Only Express crashes

Only Worker crashes

Communication

Via MySQL/Redis

Scaling

Multiple instances

Usually 1 instance

There are no rows in this table

⁠

Đặc điểm:

✅ Chạy liên tục background

✅ Có cron job (node-cron)

✅ Gửi email

✅ Process scheduled tasks

❌ KHÔNG handle HTTP request

❌ KHÔNG có port

⁠

Communication Flow

Key Points:

Express và Worker KHÔNG nói chuyện trực tiếp

Giao tiếp qua MySQL database

Express write vào database

Worker read từ database

Decoupled architecture = Reliable & Scalable

⁠

PM2 Ecosystem Management

PM2 là gì?

PM2 = Process Manager for Node.js

Chức năng:

Start/stop/restart processes

Monitor processes (CPU, memory)

Auto-restart on crash

Auto-start on server boot

Log management

Cluster mode

Zero-downtime reload

⁠

Installation

⁠

Basic Commands

⁠

Ecosystem Config File

File: ecosystem.config.js (project root)

⁠

Usage with Ecosystem

⁠

Auto-Start on Server Boot

Test:

⁠

Log Management

Setup log rotation:

Result:

Logs > 10MB → auto-rotate

Keep last 7 files

Compress old logs

Check every 30 seconds

⁠

🐛 Troubleshooting

Issue 1: Cron Not Running

Symptoms:

Worker starts but no logs

Jobs not processed

Debug:

Solution:

Verify cron syntax

Check server time: date

Ensure worker is running: pm2 status

⁠

Issue 2: Jobs Stuck in Processing

Symptoms:

Jobs have status = 'processing'

Never complete

Debug:

Solution:

⁠

Issue 3: Memory Leak

Symptoms:

Worker memory increases over time

PM2 restarts worker frequently

Debug:

Solution:

⁠

Issue 4: Multiple Workers Running

Symptoms:

Jobs processed twice

Duplicate emails sent

Debug:

Solution:

⁠

Issue 5: PM2 Not Auto-Starting on Boot

Symptoms:

After server reboot, workers not running

Debug:

Solution:

⁠

🎓 Summary

Key Takeaways:

node-cron = Schedule jobs in Node.js

Cron syntax: * * * * * = Every minute

Separate processes: Express ≠ Worker

Communication: Via database (MySQL)

PM2: Manage multiple processes

ecosystem.config.js: Define all processes

Graceful shutdown: Handle SIGTERM/SIGINT

Error handling: Try-catch, retry logic

Monitoring: PM2 logs, metrics, alerts

Production: Auto-start, auto-restart, log rotation

⁠

Learning Path:

🔰 PHASE 1: Simple Cron (Console Log)

Step 1: Install

Step 2: Tạo Simple Worker

Step 3: Test

Step 4: Multiple Schedules

📝 PHASE 2: Database Integration

Step 1: Setup Database (ví dụ Sequelize)

Step 2: Tạo DB Worker

Step 3: Test DB Worker

🚀 PHASE 3: Production Worker

Step 1: Database Schema

Step 2: Email Worker

Express vs Worker Processes

Khái Niệm Cốt Lõi

Comparison Table

Communication Flow

PM2 Ecosystem Management

PM2 là gì?

Installation

Basic Commands

Ecosystem Config File

Usage with Ecosystem

Auto-Start on Server Boot

Log Management

🐛 Troubleshooting

Issue 1: Cron Not Running

Issue 2: Jobs Stuck in Processing

Issue 3: Memory Leak

Issue 4: Multiple Workers Running

Issue 5: PM2 Not Auto-Starting on Boot

🎓 Summary

Key Takeaways:

Learning Path:

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