I Replaced Cron Jobs with Node Cron in My SaaS. Here's What Broke.

node-cron seems like the obvious choice when you're building a Node.js SaaS and need scheduled tasks. It integrates into your codebase, uses familiar cron syntax, and takes about five minutes to set up. The problem is that it also fails in ways that are hard to notice until they hit production. I used node-cron for scheduling digest emails, session cleanup, and third-party data syncs. Here's every problem I encountered, why it happened, and what I replaced it with. What node-cron actually does It runs cron jobs inside your Node process. That's the entire value proposition. npm install node-cron import cron from 'node-cron'; cron.schedule('0 8 * * *', () => { sendDailyDigestEmails(); }); No external scheduler. No separate process. The job lives and dies with your Node app. That convenience also causes all the issues listed below. Problem 1: Multiple instances run the same job We were running two app instances for redundancy. Both had the same codebase. At 8 AM, both instances execute