Scheduling Configuration - Price Tracker Bot

Overview

The Price Tracker Bot uses node-cron to schedule automated tasks. Two main cron jobs run continuously:

Daily Summary - Sends product list to all registered chats at 20:00
Price Checks - Scrapes Amazon prices every 2 hours and notifies on price drops

Both schedules use standard cron syntax and run based on the server’s system timezone.

Cron Job Implementation

The bot imports and uses the node-cron library:

index.mjs (line 4)

import cron from "node-cron";

All cron schedules run in the bot’s process. If the bot is stopped, scheduled tasks won’t execute until it restarts.

Daily Summary Schedule

Schedule Configuration

The daily summary runs at 20:00 (8:00 PM) server time:

index.mjs (lines 719-730)

// Daily summary at 20:00 (server timezone)
cron.schedule("0 20 * * *", async () => {
  console.log("📄 Envío de resumen diario...");
  for (const chatId of chats) {
    try {
      await dailySummary(chatId);
      await new Promise(r => setTimeout(r, 400));
    } catch (err) {
      console.error(`❌ Error enviando resumen a ${chatId}:`, err.message);
    }
  }
});

Cron Syntax Breakdown

"0 20 * * *"
 │ │  │ │ │
 │ │  │ │ └─── Day of week (0-7, Sunday=0 or 7)
 │ │  │ └───── Month (1-12)
 │ │  └─────── Day of month (1-31)
 │ └────────── Hour (0-23)
 └──────────── Minute (0-59)

Translation: At minute 0 of hour 20, every day

Daily Summary Schedule

string

default:"0 20 * * *"

Cron expression for when to send daily product summaries to all registered chats.

What the Daily Summary Does

Iterates through all registered chats stored in the chats Set
Sends interactive product list with buttons for each tracked product
Adds 400ms delay between messages to avoid Telegram rate limits
Handles errors gracefully - failures for one chat don’t stop others

Users receive a message with inline buttons to view details, check charts, or manage their tracked products.

Price Check Schedule

Schedule Configuration

Price checks run every 2 hours:

index.mjs (lines 732-740)

// Check prices every 2 hours
cron.schedule("0 */2 * * *", async () => {
  console.log("🔄 Cron: revisión automática de precios...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Cron Syntax Breakdown

"0 */2 * * *"
 │ │   │ │ │
 │ │   │ │ └─── Day of week (any)
 │ │   │ └───── Month (any)
 │ │   └─────── Day of month (any)
 │ └─────────── Hour (every 2 hours)
 └───────────── Minute (at minute 0)

Translation: At minute 0 of every 2nd hour (00:00, 02:00, 04:00, …, 22:00)

Price Check Schedule

string

default:"0 */2 * * *"

Cron expression for when to scrape product prices and check for changes.

Execution Times

With the */2 pattern, checks occur at:

Time	Execution
00:00	✅ Midnight check
02:00	✅ Early morning
04:00	✅
06:00	✅
08:00	✅ Morning
10:00	✅
12:00	✅ Noon
14:00	✅ Afternoon
16:00	✅
18:00	✅ Evening
20:00	✅ (+ Daily Summary)
22:00	✅ Night

Total: 12 price checks per day (every 2 hours)

What Price Checks Do

Launch Chromium browser via Playwright
Visit each tracked product URL on Amazon
Scrape current price and compare to stored value
Detect price drops and calculate savings
Send notifications to all registered chats for price reductions
Update price history (keeping last 120 entries per product)
Save data to persistence file

Price checks can take several minutes if you’re tracking many products. Each product is scraped sequentially with 900ms delays between requests.

Modifying Schedules

Changing Check Frequency

To check prices more or less frequently, modify the cron expression:

cron.schedule("0 * * * *", async () => {
  console.log("🔄 Cron: revisión automática de precios...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Recommended frequency: Every 2-4 hours balances timely notifications with server load and Amazon rate limiting.

Changing Daily Summary Time

To send summaries at a different time, modify the hour value:

cron.schedule("0 8 * * *", async () => {
  console.log("📄 Envío de resumen diario...");
  for (const chatId of chats) {
    try {
      await dailySummary(chatId);
      await new Promise(r => setTimeout(r, 400));
    } catch (err) {
      console.error(`❌ Error enviando resumen a ${chatId}:`, err.message);
    }
  }
});

Disabling Scheduled Tasks

To disable a cron job, comment it out or remove it:

// Disabled: Daily summary
// cron.schedule("0 20 * * *", async () => {
//   console.log("📄 Envío de resumen diario...");
//   ...
// });

// Price checks still active
cron.schedule("0 */2 * * *", async () => {
  console.log("🔄 Cron: revisión automática de precios...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Users can still manually trigger price checks using the /check command or ”🔄 Revisar precios ahora” button.

Advanced Cron Patterns

Business Hours Only

Check prices only during business hours (9 AM - 6 PM, Monday-Friday):

cron.schedule("0 9-18 * * 1-5", async () => {
  console.log("🔄 Cron: revisión automática de precios...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Pattern breakdown: 0 9-18 * * 1-5

Minute: 0 (top of the hour)
Hour: 9-18 (9 AM through 6 PM)
Day of month: * (any)
Month: * (any)
Day of week: 1-5 (Monday through Friday)

Weekend Only

Check prices only on weekends:

cron.schedule("0 */3 * * 0,6", async () => {
  console.log("🔄 Cron: revisión automática de precios (fin de semana)...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Pattern: 0 */3 * * 0,6 - Every 3 hours on Sunday (0) and Saturday (6)

Multiple Daily Summaries

Send summaries twice per day:

cron.schedule("0 9,21 * * *", async () => {
  console.log("📄 Envío de resumen diario...");
  for (const chatId of chats) {
    try {
      await dailySummary(chatId);
      await new Promise(r => setTimeout(r, 400));
    } catch (err) {
      console.error(`❌ Error enviando resumen a ${chatId}:`, err.message);
    }
  }
});

Pattern: 0 9,21 * * * - At 9:00 AM and 9:00 PM daily

Timezone Considerations

Server Timezone

Cron jobs run based on the server’s system timezone, not user timezones. Check your server timezone:

date
timedatectl  # On Linux with systemd

Example output:

Mon Mar 10 14:30:00 PST 2026
Time zone: America/Los_Angeles (PST, -0800)

If your server is in UTC but you want schedules in Pacific Time, adjust the hour values accordingly. For example, 20:00 PST = 04:00 UTC the next day.

Setting Server Timezone

On Linux:

# Set to Pacific Time
sudo timedatectl set-timezone America/Los_Angeles

# Set to UTC
sudo timedatectl set-timezone UTC

# Set to Eastern Time
sudo timedatectl set-timezone America/New_York

On Docker:

docker-compose.yml

services:
  price-tracker:
    image: price-tracker
    environment:
      - TZ=America/Los_Angeles
    volumes:
      - /etc/localtime:/etc/localtime:ro

Restart the bot after changing the system timezone for cron schedules to use the new timezone.

Performance Optimization

Rate Limiting

The bot includes delays to avoid overwhelming Amazon and Telegram: Between products during price checks (index.mjs:214):

await new Promise((r) => setTimeout(r, 900));

Between chat notifications (index.mjs:242):

await new Promise((r) => setTimeout(r, 500));

Between daily summaries (index.mjs:725):

await new Promise(r => setTimeout(r, 400));

Adjusting Delays

If you encounter rate limiting, increase these delays:

// Slower scraping to avoid detection
await new Promise((r) => setTimeout(r, 2000));  // 2 seconds instead of 900ms

// More conservative Telegram messaging
await new Promise((r) => setTimeout(r, 1000));  // 1 second instead of 500ms

Longer delays mean slower price checks but reduced risk of being rate-limited or blocked by Amazon.

Memory Management

With many products, the history can grow large. The HISTORY_LIMIT prevents unbounded growth:

index.mjs (lines 69, 196)

const HISTORY_LIMIT = 120;

// In checkPrices function:
updated.history.push({ date: new Date().toISOString(), price: scraped.price });
if (updated.history.length > HISTORY_LIMIT) 
  updated.history = updated.history.slice(-HISTORY_LIMIT);

Memory impact:

10 products × 120 history entries × ~50 bytes = ~60 KB
100 products × 120 history entries × ~50 bytes = ~600 KB

For tracking 100+ products, consider reducing HISTORY_LIMIT to 60 (5 days of history) or increasing price check intervals to every 4 hours.

Monitoring and Debugging

Console Logging

The bot outputs cron execution logs:

🔄 Cron: revisión automática de precios...
⏳ Iniciando revisión de precios...
🎉 2 productos cambiados — notificando a 3 chats.

Verifying Cron Syntax

Use crontab.guru to validate and understand cron expressions:

0 20 * * * → “At 20:00”
0 */2 * * * → “At minute 0 past every 2nd hour”

Testing Schedules

To test without waiting for scheduled times, temporarily change to run every minute:

// TESTING ONLY - runs every minute
cron.schedule("* * * * *", async () => {
  console.log("🔄 Test: revisión automática de precios...");
  try {
    await checkPrices();
  } catch (err) {
    console.error("❌ Error en cron checkPrices:", err.message);
  }
});

Do not use * * * * * in production! It runs every minute and will quickly exhaust resources and trigger rate limits.

Manual Execution

Via Telegram Commands

Users don’t need to wait for scheduled checks:

/check - Manually trigger price check for all products
/list - View daily summary UI without waiting for 20:00

Via Code

Call the functions directly for testing:

// Manually invoke price check
await checkPrices();

// Send summary to specific chat
await dailySummary(123456789);

Troubleshooting

Cron Jobs Not Running

Symptom: Scheduled tasks never execute Solutions:

Verify bot is running continuously (not restarting)
Check console for syntax errors in cron expressions
Ensure node-cron is installed: npm list node-cron

Wrong Execution Times

Symptom: Tasks run at unexpected hours Solutions:

Check server timezone: date
Verify cron expression using crontab.guru
Remember: 20:00 server time may differ from your local time

Duplicate Executions

Symptom: Price checks run multiple times per hour Solution: Ensure you haven’t defined the same cron schedule multiple times in the code

Rate Limiting

Symptom: Amazon blocks requests or Telegram rate limits messages Solutions:

Increase delays between requests (see Performance Optimization)
Reduce check frequency (every 4 hours instead of 2)
Use residential proxies for Amazon requests (advanced)

Next Steps

Setup Guide

Review initial setup and configuration

Environment Variables

Configure Telegram bot token and secrets

Getting Started

Features

Commands

Configuration

Technical Details

Support

​Overview

​Cron Job Implementation

​Daily Summary Schedule

​Schedule Configuration

​Cron Syntax Breakdown

​What the Daily Summary Does

​Price Check Schedule

​Schedule Configuration

​Cron Syntax Breakdown

​Execution Times

​What Price Checks Do

​Modifying Schedules

​Changing Check Frequency

​Changing Daily Summary Time

​Disabling Scheduled Tasks

​Advanced Cron Patterns

​Business Hours Only

​Weekend Only

​Multiple Daily Summaries

​Timezone Considerations

​Server Timezone

​Setting Server Timezone

​Performance Optimization

​Rate Limiting

​Adjusting Delays

​Memory Management

​Monitoring and Debugging

​Console Logging

​Verifying Cron Syntax

​Testing Schedules

​Manual Execution

​Via Telegram Commands

​Via Code

​Troubleshooting

​Cron Jobs Not Running

​Wrong Execution Times

​Duplicate Executions

​Rate Limiting

​Next Steps

Setup Guide

Environment Variables

Build docs developers (and LLMs) love

Overview

Cron Job Implementation

Daily Summary Schedule

Schedule Configuration

Cron Syntax Breakdown

What the Daily Summary Does

Price Check Schedule

Schedule Configuration

Cron Syntax Breakdown

Execution Times

What Price Checks Do

Modifying Schedules

Changing Check Frequency

Changing Daily Summary Time

Disabling Scheduled Tasks

Advanced Cron Patterns

Business Hours Only

Weekend Only

Multiple Daily Summaries

Timezone Considerations

Server Timezone

Setting Server Timezone

Performance Optimization

Rate Limiting

Adjusting Delays

Memory Management

Monitoring and Debugging

Console Logging

Verifying Cron Syntax

Testing Schedules

Manual Execution

Via Telegram Commands

Via Code

Troubleshooting

Cron Jobs Not Running

Wrong Execution Times

Duplicate Executions

Rate Limiting

Next Steps