Investigate Recurring Bugs and Prevent the Same Failure from Returning

A production bug keeps recurring after apparent fixes. How would you investigate it and change the engineering process or system so that the same failure does not continue to return? ### Constraints No specific bug, language, or architecture is supplied. Use an actual example with accurate ownership or label your example hypothetical. Distinguish repeated instances of the same underlying defect from different defects that share a symptom. ### Clarifying Questions - Do the incidents share a signature, triggering conditions, and code path? - What did each previous fix change, and what evidence supported closing the incident? - Did the bug recur on the same version, after a rollback, or after a later change? ```hint Compare the previous fixes A pattern in what earlier fixes failed to cover can reveal the missing invariant, test, or ownership boundary. ``` ### What a Strong Answer Covers - Reproduction and comparison of incidents before selecting a permanent fix. - A causal explanation, targeted regression coverage, and a safe rollout. - Ownership, monitoring, and criteria for verifying that recurrence risk has decreased. ### Follow-up Questions - How would you handle a recurrence that cannot be reproduced locally? - When is a design change justified instead of another localized patch?