> Still, this type of oversight seems all too common even in large companies. (...) Has anyone developed a tool designed specifically to avoid certificate expiry disasters?
LetsEncrypt renewal is supposed to be automated. [1]
I know of a company that hosted blogs for thousands of customers. They used LetsEncrypt, but the CTO considered automatic renewals a possible security risk, so they did it manually. Problem is, the expiration happened in a weekend and they "forgot" to update the certificates before that. Suffice to say that the next Monday wasn't pleasant. They automated after that.
[1] https://letsencrypt.org/about/