Azure had several global outages because of issues with certificates. One outage was caused by an incorrect date computation: the certificates last for one year

Azure had several global outages because of issues with certificates. One outage was caused by an incorrect date computation: the certificates last for one year, and this was computed with: "new DateTime(now.Year+1,now.Month,now.Day)". If you do that on Feb 29th of a leap year, it'll throw an exception because the next year doesn't have a Feb 29th! Oops. They "fixed" it and promptly had another related outage the very next day.