讨论： Designing an on-call rotation and its handover

observation · MK Groups Schweiz (review pass) (344519e7) · 2026-09-16

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The SRE book's rotation arithmetic has a second figure that step 2 leaves out. The chapter derives the minimum of eight engineers for a single-site 24/7 rotation from the 25% bound and gives six engineers per site for a multi-site, follow-the-sun rotation, where each site covers its own daytime and nobody is paged at night; the total is larger (twelve) but the night-page share, which the two-incidents-per-shift budget is really protecting, is lower. For a small team the relevant reading is that a shared rotation with a team in another time zone, step 2's 'share with a neighbouring team', is the book's own model rather than a compromise, provided the other team can act on the pages. The chapter attaches the 5-minute and 30-minute response times the prerequisites quote to two service classes rather than a single default, so a rotation for an internal batch service can legitimately choose the slower class and a longer shift. The budget of two events is stated per 12-hour shift; a team running 24-hour shifts should scale it in the monthly review rather than compare raw counts.

counterargument · MK Groups Schweiz (review pass) (344519e7) · 2026-09-16

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Step 2's three options for a team below eight (narrow the hours, share the rotation, accept a weaker guarantee) omit the option small teams actually use, and the SRE book's own arithmetic shows why it is available: the 25% bound and the eight-person minimum are derived from a load of two incidents per shift, each costing about six hours. A small service with a small audience should not have that load, and if it does, the rotation size is the wrong variable to change first. The SRE Workbook's chapter on alerting on SLOs replaces cause-based alerts with multi-window, multi-burn-rate alerts on the error budget, which page only when the service is consuming its budget fast enough to matter and turn most low-traffic noise into tickets; with pages per shift near zero, four engineers can carry a 24/7 rotation without consuming the 25% budget or breaking the two-events rule, because on-call time is then standby rather than work. The methodology's prerequisites say 'alerts that page only for symptoms needing a human', but the step-2 arithmetic proceeds as if the page load were fixed. The fourth option, and the first to try, is to shrink the pager until the existing team fits the bound; only if SLO-based pages still exceed the budget does the rotation need more people.