n8n Workflow: Auto Rotate On-Call Using Google Calendar + Slack

Automatically rotate weekly on-call duty—using Google Calendar, Slack, and public holidays

This n8n workflow automatically chooses the fairest available on-call engineer each week, creates/updates the on-call marker in Google Calendar, and coordinates handovers in Slack—including leave coverage and region-aware public holidays via the Nager.Date API.

What this workflow does

• Triggers on schedule and edits: runs every Thursday at 10:00 and also triggers whenever an on-call Google Calendar event is updated.
• Builds scheduling context: reads past on-call events plus upcoming leave events from Google Calendar, then fetches public holidays using the Nager.Date API.
• Selects the most suitable assignee: calculates the target on-call week and picks the best available person based on recent on-call history, required rest weeks, leave events, and region-specific public holidays.
• Creates and announces assignments: if the weekly run finds no on-call event yet, it creates an all-day on-call event in Google Calendar and posts the assignment to a Slack channel.
• Coordinates handover: waits until the configured handover time, then updates the Slack channel topic to reflect the current on-call person.
• Manages swaps safely: when an edit looks like a swap, it validates the new assignee against the same rules and sends an approval request in Slack. If approved, it updates the Google Calendar marker and confirms in Slack; if not, it reverts the change and posts the reason.

Use cases

• Weekly on-call rotations for SaaS teams who need equitable distribution.
• Coverage planning that accounts for individual leave and public holidays automatically.
• Slack-based approval flow for controlled on-call swaps.
• Teams that want a single source of truth (Google Calendar) and live channel visibility (topic updates).

Technical details

• Integrations: Google Calendar (OAuth2), Slack, Nager.Date API
• n8n nodes/logic used: set, code, wait, merge, slack, switch
• Setup: configure OAuth2 credentials and select the on-call calendar + leave calendar, including the “On-Call Week Edited” trigger.