What is On-call?

On-call is the arrangement where a named person is responsible for responding to alerts for a service during a defined period, including outside working hours. It has three parts: the roster (who is in the pool), the rotation (the rule that advances through the pool) and the schedule (the resulting calendar of shifts).

Common rotation lengths are one day to one week; a week is the usual maximum before fatigue sets in. Healthy on-call needs a small number of actionable alerts, a secondary to escalate to, easy overrides for holidays, and time off after a bad shift.