A global outage of core business communication services lasting several hours affected millions of users, resulting in reputational damage for Microsoft despite the technical cause being simple.
Expiring certificates are among the easiest edge cases to test—provided the renewal process itself is regularly tested against actual expiration dates, rather than just testing the application during normal operation. A monitoring system that actively checks certificate expiration dates well in advance and simulates the renewal process in test environments (instead of simply relying on automation) would have prevented this outage. This is precisely the essence of a structured monitoring and reporting approach.

Both cases demonstrate that not every outage stems from a complex code bug. Sometimes the issue lies in operational processes—such as certificate renewals or security updates—that were never tested under realistic conditions; other times, it involves a test matrix that simply fails to cover an entire class of devices. In both instances, a structured testing approach extending into operations would have exposed the vulnerability beforehand.