SYSE.37:4.2 - Derive a budget-risk rule on the right basis

For an event-ratio SLO below 100%, let s be the agreed good-event target and e the observed bad-event fraction for the same eligible population. The normalized burn rate is e / (1 - s). Its meaning depends on the quality and coverage of those observations.

Choose the budget fraction p that warrants action and a decision window w within objective period T. Under a consistent event-rate assumption, the corresponding threshold is p × T / w. If traffic changes materially, relate the actual event counts to the objective’s budget rather than treating elapsed time as an exact share of that budget.

Where useful, pair the longer decision window with a shorter confirmation window to distinguish accumulated loss from continuing high consumption. Select additional slower-risk coverage only when its distinct response is needed. More windows increase rule and notification complexity.

A maximum possible burn rate can be below a proposed threshold for a loose objective. Check that the rule can fire for the failures it is intended to detect. For an objective of 100%, s = 1, so e / (1 - s) is undefined; use a different qualified alerting rule.