Monitor workflow heartbeats with Google Sheets and Slack alerts

Description

Quick overview
This workflow implements a dead man’s switch for scheduled jobs by recording heartbeat check-ins via a web-hook to Google Sheets and alerting to Slack when a job misses its expected run window, with optional recovery notifications when the job starts checking in again.

How it works
Receives a POST webhook heartbeat containing a job_id and validates an x-heartbeat-secret header against a configured shared secret.
Looks up the job_id in a Google Sheets “jobs” registry and returns a 404 response if the job is not registered.
Updates the matching Google Sheets row with the current last_heartbeat timestamp, sets status to OK, and clears last_alert_at.
If the job was previously in an alerting state, posts a recovery message to the configured Slack channel.
Responds to the heartbeat request with a 200 JSON confirmation including the job_id and recorded timestamp.
Every 15 minutes, loads all active jobs from Google Sheets and calculates which ones are overdue based on expected_every_minutes plus a grace period, suppressing repeat alerts for a configured re-alert window.
For each overdue job, posts a missed-run (or never-seen) alert to Slack and writes back last_alert_at and status in Google Sheets to prevent immediate re-alerting.

Setup
Create or copy a Google Sheets document with a “jobs” sheet containing columns such as job_id, job_name, expected_every_minutes, grace_minutes, last_heartbeat, status, last_alert_at, active, and alert_channel.
Add Google Sheets OAuth2 credentials and replace YOUR_SHEET_ID in all Google Sheets steps with your spreadsheet ID.
Add Slack credentials and set the target channel (or use per-row alert_channel) in the Slack alert and recovery message steps.
Set a strong shared_secret in the receiver configuration and have each monitored job send it in the x-heartbeat-secret header when POSTing to the webhook.
Add one row per monitored job (set active to TRUE, expected_every_minutes, and optional grace_minutes/alert_channel) and configure your jobs to POST their job_id to the webhook URL on successful completion.

Requirements
Google Sheets account with edit access, used as the job registry and heartbeat log
Slack workspace with a bot/app that can post to the alert channel(s)
Each monitored job needs to be able to send an HTTP POST request on completion (a script, a cron job, or another n8n workflow)
A self-hosted or cloud n8n instance that can receive inbound webhooks

Customization
Swap Slack for email, Telegram, Discord, or PagerDuty by replacing the two Slack nodes
Move the registry from Google Sheets to Airtable or Postgres if job volume outgrows a spreadsheet
Adjust default_grace_minutes and re_alert_after_minutes in "Set checker config" to tune alert sensitivity and repeat-alert frequency
Set a per-row alert_channel in the sheet to route different jobs to different Slack channels
Change the schedule trigger's interval (default 15 minutes) to check more or less often

Additional info
The webhook is public by design, since any job can POST a heartbeat to it. The shared_secret check in "Validate shared secret" isn't optional hardening, it's the only thing stopping a stranger from spoofing check-ins and silencing your alerts. Treat it like an API key.