When I was a contractor, this happened to one of my customers that was under contract (I set up the cert initially). I fixed the issue overnight without major i

When I was a contractor, this happened to one of my customers that was under contract (I set up the cert initially). I fixed the issue overnight without major impact, but boy was I embarrassed by the bush-league mistake. Since then, in addition to service monitoring, I've taken to calendaring certificate expiration dates ~14 days before they expire. Low tech but I've never forgotten since.