How to Debug Cron Job Failures: Message Failed vs Execution Failed

TL;DR When cron jobs report "Message failed," the actual task execution might have succeeded. This article explains how to separate the reporting layer (Slack/email delivery) from the execution layer (actual processing) to debug efficiently. Based on a real case where 68% of cron jobs showed "Message failed" on Sunday, but execution logs revealed some tasks completed without errors. Prerequisites Cron jobs that send results to Slack/email Access to log files or output files Shell environment (bash/zsh) The Problem: "Message Failed" Everywhere Sunday morning, the monitoring dashboard showed this: Time Range Success Failed Success Rate 03:00-15:30 0/14 14/14 0% 18:00-23:30 7/7 0/7 100% Total 7/22 15/22 30% All error messages: "Message failed." This alone does not tell you what actually failed. Two Layers Cron job failures must be analyzed in two layers: [Execution Layer] Task logic (data fetching, file generation, API calls) ↓ [Reporting Layer] Result delivery (Slack post, email send) "M