Aim for a rotation that is sustainable and rare enough to stay sharp: weekly shifts with a primary and a documented escalation path, handover notes at the start of each shift, and compensation or time back for out of hours work. Only page for things that are urgent, user visible, and actionable; everything else becomes a ticket. Track the page count per shift and treat sustained noise as a defect to fix.
Why interviewers ask this
On call design tells the interviewer how you treat people and whether you close the loop between operations and engineering. They want to hear about actionable alerts, escalation, runbooks and compensation, and about measuring the load. A candidate who talks only about tooling and not about sleep, fairness and reducing pages is one who will burn a team out.
How to structure your answer
- Set the shape: shift length, primary, secondary, escalation.
- Define the bar for what may page a human at night.
- Cover runbooks, handover, and onboarding a new on caller.
- Measure page load and feed it back into engineering work.
Example answer
With six people a weekly primary rotation works, so each person is on roughly every six weeks, plus a secondary who gets escalated to after ten minutes of no acknowledgement so nothing depends on one phone being charged. The rule I hold firmly is that a page has to be urgent, user affecting and actionable. If the response is to look at it and go back to sleep, it should never have been a page, and it becomes a ticket instead. Every alert needs a runbook link with the first three things to check, otherwise a new joiner is doing archaeology at three in the morning. Shifts start with a handover, even if it is two lines, and end with a short note about anything still smoldering. People get time back for night work, non negotiable. And I track pages per shift as a real metric, because if it goes above roughly two a week I stop treating it as an on call problem and start treating it as an engineering backlog problem; the fix is deleting the cause of the alert, not being tougher about the rotation.
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See how it worksFollow-up questions to expect
- How do you onboard someone onto on call for the first time?
- What would you do if one service generates most of the pages?
- How do you handle on call for a team spread across time zones?
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